ifm electronic gmbh Sensors, networking and control ... · section instead of a keyword. To differentiate them from simple keywords, they are written in italics. 2.1 On the contents

ifm electronic gmbh

Sensors, networkingand control technology

for automation

Training manual

Shaft Encoders

Training manual for shaft encoders (September 2003)

Guarantee note:

All data published using this medium are ifm's intellectual property or were given to ifm by customers or suppliers forexclusive use. We explicitly point out that no part of this publication may be used (in particular reproduced,distributed and placed in the public domain) nor modified or rearranged without prior written permission by ifm.This manual was written with the utmost care. Neverthele ss, we cannot guarantee that the contents are correct andcomplete.Since errors cannot be avoided despite a ll efforts we appreciate your comments.ifm electronic gmbh, VTD-STV department, Teichstr. 4, 45127 Essen, phone: +49 201/2422-0,Internet: http://www.ifm-electronic.com

Contents:

1 Introduction........................................................................................................................ 61.1 Measuring systems........................................................................................................... ....... 6

1.1.1 Shaft encoders as a standard means of measuring .....................................................................6

1.2 Applications for shaft encoders ............................................................................................. .. 61.2.1 Rotational movement.................................................................................................................71.2.2 Linear movement .......................................................................................................................7

1.3 Application examples of shaft encoders................................................................................... 71.4 Digital signals............................................................................................................. ............. 81.5 Measuring device and measuring system ................................................................................. 9

2 Layout .............................................................................................................................. 102.1 On the contents ............................................................................................................. ....... 10

3 Techniques and methods of electronic linear measurement ............................................... 113.1 Analogue systems ............................................................................................................ ..... 11

3.1.1 Potentiometers.........................................................................................................................113.1.2 Resolvers ..................................................................................................................................113.1.3 Inductive principle ....................................................................................................................123.1.4 Magnetic principle ...................................................................................................................123.1.5 Capacitive principle ..................................................................................................................13

3.2 Digital systems ............................................................................................................. ......... 133.2.1 Mechanical shaft encoders .......................................................................................................133.2.2 Oscillator sensors .....................................................................................................................143.2.3 Inductive system.......................................................................................................................143.2.4 Photoelectric shaft encoders ....................................................................................................14

4 Shaft encoders of ifm electronic........................................................................................ 164.1 DIADUR method ............................................................................................................... .... 164.2 Shaft encoder types of ifm electronic..................................................................................... 17

5 Shaft encoders.................................................................................................................. 185.1 Incremental shaft encoders.................................................................................................. .. 18

5.1.1 Shape and design.....................................................................................................................185.1.2 Coded disc ...............................................................................................................................195.1.3 Resolution - mechanical ...........................................................................................................205.1.4 Signal generation .....................................................................................................................205.1.5 Pulse generation and analogue signals .....................................................................................235.1.6 Wiring of an incremental encoder ............................................................................................275.1.7 Detection of the direction of rotation for the direction of counting..........................................285.1.8 Pulse multiplication ..................................................................................................................29

5.2 Absolute shaft encoders..................................................................................................... ... 305.2.1 Resolution ................................................................................................................................325.2.2 Singleturn shaft encoders.........................................................................................................325.2.3 Multiturn shaft encoders ..........................................................................................................345.2.4 Code types...............................................................................................................................35

5.3 Comparison of absolute shaft encoders and incremental shaft encoders................................ 39

5.4 Data transmission ........................................................................................................... .......405.4.1 SSI interface on the shaft encoder ............................................................................................405.4.2 SSI interface programming via software ...................................................................................435.4.3 SSI controller ............................................................................................................................445.4.4 Profibus-DP interface................................................................................................................46

5.5 Accuracy of the shaft encoder ............................................................................................... 485.5.1 Dividing error ...........................................................................................................................495.5.2 Mark-to-space ratio..................................................................................................................495.5.3 Phase difference.......................................................................................................................49

6 Mechanical design............................................................................................................ 516.1 Solid shaft encoders ........................................................................................................ ......51

6.1.1 Flange types for solid shaft encoders ........................................................................................52

6.2 Hollow shaft encoders ....................................................................................................... ....546.2.1 Mounting of hollow shaft encoders.......................... ................................................................55

7 Electrical connection......................................................................................................... 567.1 Connection cable ............................................................................................................ ......567.2 Connector ................................................................................................................... ..........57

7.2.1 Sockets/coupling ......................................................................................................................58

7.3 Laying the cable ............................................................................................................ ........597.4 Earthing and screening ...................................................................................................... ....59

8 Mechanical data ............................................................................................................... 608.1 Maximum mechanical rotational speed ..................................................................................60

8.1.1 Mechanical rotational speed of the shaft encoder . ...................................................................60

8.2 Shaft load.................................................................................................................. ............618.3 Shock resistance and vibration resistance ...............................................................................628.4 Housing material ............................................................................................................ .......628.5 Protection rating........................................................................................................... .........628.6 Operating temperature ....................................................................................................... ...62

9 Electrical data ................................................................................................................... 649.1 Voltage supply.............................................................................................................. .........649.2 Voltage supply via the external evaluation electronics ............................................................659.3 Sensor cables for encoders.................................................................................................. ...659.4 Current consumption ......................................................................................................... ...66

9.4.1 Light-emitting diodes (LEDs) .....................................................................................................66

9.5 Current rating of the signal outputs.......................................................................................679.6 Signal frequency............................................................................................................ ........67

9.6.1 Signal frequency and mechanical rotational speed ...................................................................679.6.2 Signal frequency and cable length............................................................................................68

10 Overview shaft encoders................................................................................................... 7011 Operating instructions ...................................................................................................... 7112 Data sheet........................................................................................................................ 7213 Accessories....................................................................................................................... 74

13.1 Couplings for solid shaft encoders......................................................................................... 7413.2 Angle flanges.............................................................................................................. .......... 7613.3 Bearing block .............................................................................................................. .......... 7613.4 Isolating adapter .......................................................................................................... ......... 7713.5 Pinion and rack ............................................................................................................ ......... 7713.6 Resilient base ............................................................................................................. ........... 7813.7 Measuring wheel ............................................................................................................ ...... 7813.8 Fastening clamp ............................................................................................................ ........ 8013.9 Pulse divider, pulse stretcher............................................................................................. ..... 80

13.9.1 Pulse divider .............................................................................................................................8113.9.2 Pulse stretcher..........................................................................................................................81

14 Mounting of shaft encoders.............................................................................................. 8215 Calculation examples ........................................................................................................ 84

15.1 Linear measurement......................................................................................................... ..... 8415.2 Switching frequency and mechanical rotational speed ........................................................... 84

16 Handling of shaft encoders ............................................................................................... 8517 Applications...................................................................................................................... 8618 Annex............................................................................................................................... 89

18.1 Competitors................................................................................................................ .......... 8918.2 Glossary of technical terms................................................................................................ .... 89

19 Type key ........................................................................................................................... 9319.1 Examples of the use of the type key ...................................................................................... 94

20 List of figures.................................................................................................................... 9521 Index ................................................................................................................................ 9822 Source ............................................................................................................................ 100

Training manual Shaft encoders Page 6 of 100

1 IntroductionIn all areas of technology production and test processes are automated toan increasing extent. If only end stops or reference points are to bemonitored, inductive or capacitive proximity switches or photoelectricsensors are the preferred choice.

1.1 Measuring systemsTools of automation The mechanical movements of robot arms, linear slides, rotary tables or

slides often have to be controlled numerically. Measuring systems forlengths, angles and partial steps provide feedback about these movementsto the controller.

1.1.1 Shaft encoders as a standard means of measuring

Encoders are needed if high precision and short measuring times arerequired and if the processing of the information is to be carried out bymeans of electronic control systems.In the following especially angular and linear measurement will bediscussed. There is a variety of measuring methods which will be brieflydescribed below.

Reliable Shaft encoders are standard units for angular and linear measurement. Inmany manufacturing and production processes they are indispensable asreliable transducers or pulse pickups.Shaft encoders are used where precise detection of lengths, positions,rotational speed, and angles is required.

Function Shaft encoders transform mechanical movements into electrical signals.

Resistant Shaft encoders have shown excellent performance in various applications,even in harsh environments with shock, dirt, changing temperatures andvibration. They are very reliable and have a long life.

Versatile The photoelectric measuring principle enables high measuring accuracy aswell as inexpensive versatile solutions which are especially adapted toautomation technology.

1.2 Applications for shaft encodersTypical applications of linear measurement systems are woodworkingmachines, machine tools, robots and handling machines, textile machines,electronic scales, plotters and printers from the IT area as well as testequipment.


1.2.1 Rotational movement

Encoders can be used without a lot of mechanical work being requiredwherever rotating machine parts are present. Flange, fixing holes andgrooves enable easy connection to the rotating part.

1.2.2 Linear movement

Nearly every linear movement is connected with a rotational movement, forexample a feed function with the rotation of a drive shaft. Furthermore alinear movement can easily be transformed into a rotational movement onthe shaft encoder by means of a measuring wheel or a rack with a toothedwheel.Therefore encoders are often used for linear measurement. To convert arotational angle into a distance a conversion factor is required which resultsfrom the geometry of the device as well as any transmission ratio or gearreduction.

1.3 Application examples of shaft encoders

Figure 1, Linear measurement and synchronous movement monitoring

Figure 2, Detection of rotational speed and angle measurement


Figure 3, Bending systems and X-Y-recorders drawing tables

Figure 4, Level measurement and radar/aerial systems

Figure 5, Industrial robots

1.4 Digital signalsThe measured values of angles or distances are in most cases required indigitised form so that they can be further processed in electronics connecteddownstream, e.g. a plc.For this reason the measurement is carried out digitally. The measuringsystem in the form of a shaft encoder assigns a digital output value to theanalogue measured value as a length or an angle.Thus the output value of the shaft encoder represents the measuredquantity in defined digital steps.Most digital length and angle measuring systems are based on standardswith a periodic structure. By using different principles of physics periodicalelectrical signals are generated from which the measured value is derived.


1.5 Measuring device and measuring systemMeasuring device The measuring disc and detection system of the encoder are also called

measuring device, sensor, transducer or encoder. They convert lengths orangles into electrical signals.

Measuring system A measuring system consists of the complete measuring chain. It mayconsist for example of a measuring disc, the scanning unit, the interpolationelectronics, and a counter.The electronics and the counter can be integrated as interface electronics inthe measuring device or the electronics connected downstream.For angle measurement the coupling between the machine shaft and themeasuring device is to be regarded as part of the measuring system as well.ifm offers two different types of unit for the measurement of angles orlengths:

incremental encodersabsolute encoders

Both the absolute and the incremental shaft encoders have advantageswhen compared with each other. They can also be combined in one unit.


2 LayoutFor a better understanding a few explanations regarding terms used in thetext will be given to make reading the text and finding information easier.

Keywords Keywords are indicated in the margin on the left, referring to the topic to bedealt with in the following section.

What does FAQ mean? This stands for Frequently Asked Questions. This term is used for example inthe context of modern electronic media. Almost everybody starting to dealwith a new unit faces the same questions. Sometimes an FAQ precedes asection instead of a keyword. To differentiate them from simple keywords,they are written in italics.

2.1 On the contentsThis manual is to provide basic information on shaft encoders. Importantterms and correlations are explained, state-of-the-art technology isdescribed and technical data of ifm-units are presented. This results in thefollowing structure.

Characteristics of the shaft encoders Other types of shaft encoders which are used are mentioned. Then follows ageneral overview of different encoder systems. This is to facilitate thecorrect classification of shaft encoders and to decide where they can beused and where they cannot be used. The knowledge of these features,their advantages and disadvantages is a prerequisite for their successful use.

ifm-units Here the data of ifm shaft encoders are stated and explained. Mechanicaldesign, electrical features and use are described. Some units are presented.

Applications A few applications with illustrations are briefly described.Annex This manual is to help you with your self-study as well. Therefore important

terms are briefly explained again in the glossary of technical terms. Thepoints which are essential for ifm shaft encoders are described in detail inthe chapters preceding the glossary. The index will help to look them up.The type key for the ifm-specific units is briefly presented as well.

Much success! Everybody should have these basics to be able to benefit from the chancethis product offers and to use shaft encoders successfully.


3 Techniques and methods of electroniclinear measurement

Electronic signal processing mainly differentiates between the processing ofanalogue and digital signals. The information which is supplied by thedifferent measuring systems is also differentiated.It is divided into analogue and digital systems/signal transmitters.

3.1 Analogue systems

3.1.1 Potentiometers

Potentiometers consist of a slide made of resistance material and a wipercontact.The wiper is only ever in contact with a small area of the resistance coil orsurface. The position of the wiper contact results in a variable resistancevalue.Areas of application: Level measurement, measurement of valve positions,temperature measurement by means of a bimetal spring.

Figure 6, Potentiometer

3.1.2 Resolvers

Resolvers are synchro generators which precisely indicate the currentposition of the rotor. They belong to the group of absolute encoders. Thedesign of the unit is similar to an electric motor or generator.Applications are robots and the military area (aeroplanes, tanks).

S3S1

S2

S4

cosine

sine

R2

R4

rotor

Figure 7, Resolver


3.1.3 Inductive principle

The units (well-known are the versions from the company Novotechnik)consist in principle of two ferrite cores which form a magnetic circuitbetween which printed coils with two closed rings are turned.Areas of application: Machine construction, conveyor technology, robots,printing industry, packaging industry, foundries, and rolling mills.

U1 U2

AM

Figure 8, Inductive principle (Novotechnik)

A: reference elementM: measuring element

3.1.4 Magnetic principle

Small permanent magnets are arranged on the circumference of a disc. TheHall sensor placed in front converts the alternating magnetic fields intoelectrical signals.


SN

U

Figure 9, Magnetic principle

3.1.5 Capacitive principle

Two plates of a capacitor are moved in relation to each other on an axle.The resulting capacitance provides information about the position of theaxle.

3.2 Digital systems

3.2.1 Mechanical shaft encoders

Mechanical shaft encoders generate a digital output signal. Switches orcontacts on a control shaft are activate d by cams. These units are also calledcam-operated switchgroups.Areas of application: Conveyor systems with low resolution, transport beltsand washing machines.

Figure 10, Mechanical shaft encoder (cam-operated switchgroup)

A cam-operated switchgroup is free from wear and tear if the mechanicalswitches from figure 10 are replaced by inductive proximity switches.


Figure 11, Cam-operated switchgroup with inductive proximity switches

3.2.2 Oscillator sensors

The oscillator sensors work according to the incremental principle andtransmit digital signals. Usually U-shaped sensors are used for non-contactdetection of a rack or a coded disc.

3.2.3 Inductive system

With this principle the teeth of a rotating toothed wheel are detected bymeans of an inductive proximity switch.

Figure 12, Inductive system

3.2.4 Photoelectric shaft encoders

On the edge of a round metal or glass disc transparent slits (segments orincrements) are arranged.Binary output signals are generated by means of through-beam sensors inminiature format and subsequent electronics. The number of incrementsdetermines the resolution of a full circle.


Figure 13, Incremental shaft encoder

The photoelectric shaft encoders are discussed in this manual.


4 Shaft encoders of ifm electronicifm electronic offers shaft encoders which function according to thephotoelectric principle. In the past ifm electronic cooperated with differentpartners.Since 1990 ifm has been working with the company Heidenhain inTraunreut.

4.1 DIADUR methodThe number of increments (bright and dark fields) on the glass disc are ofvital importance for a high resolution of the encoder. The patented DIADURmethod of Heidenhain allows to apply very fine structures on a glass disc.The DIADUR method is divided into six steps:

1. Cleaning of the glass disc (ultrasonic, without contact).2. Application of photoresist, pre-dried, hardened.

Photoresist is a light-sensitive material which is applied in liquid form toa carrier material � in this case glass.

3. The so-called working originals (negatives) are pressed onto the glassplate.

4. The complete glass surface is coated with chromium and exposed via amask.

5. The chromium is washed off with a chemical solution.6. Chromium only adheres to the glass plate where the photoresist has

been exposed.

Due to the many manufacturing steps the production of a DIADUR glassdisc is very time-consuming.The advantages of a DIADUR glass disc are:

Very good contour sharpness of the lines. This results in a very highaccuracy.The glass disc is largely resistant to chemical and mechanical influences.The system accuracy is approx. ± 1/20 grating mark for coded discswith up to 5,000 increments and ± 12 seconds of an angle for codeddiscs with more than 5,000 increments.


4.2 Shaft encoder types of ifm electronicThe following photos show the standard types of shaft encoders of ifmelectronic in alphabetical order � referred to the ifm designation. The sizesof the encoders in the photos are not to correct scale.The designation of the individual shaft encoders always starts with a capital"R". The second capital letter is the designation of the type. It refers to theflange and the type of shaft. Example: RC stands for the type with roundflange and solid shaft.

RA, incr., hollow shaft RB, incr., solid shaft RC, incr., solid shaft

RM, abs. SSI, hollow shaft RM, abs., Profibus DP, solid shaft RM, abs., SSI, solid shaft

RN, abs., parallel, solid shaft R=, incr., hollow shaft RP, incr., hollow shaft

RU, incr., solid shaft RV, incr., solid shaft


5 Shaft encodersEncoders convert mechanical movements like rotational or linearmovements (rotation and translation)into binary/digital voltage values. Theyare transducers, mainly for rotational movements.In connection with mechanical converters like measuring wheels or racksincremental shaft encoders can also be used for linear measurements.Shaft encoders function according to the principle of photoelectric detectionof the fine detection grids.Most shaft encoders are round.Even if the following information may seem superfluous: Shaft encodershave to be driven mechanically from outside on the shaft.Depending on the measuring and evaluation method a differentiation ismade between:

incremental shaft encodersabsolute shaft encoders

5.1 Incremental shaft encoders

5.1.1 Shape and design

The main components of an incremental shaft encoder are shown in figure14. They are:

shaft (solid shaft or hollow shaft)mounting flangeball bearingcoded discdetection system (LED, condenser/lens, detection grid, photo elements)electronics for generating the signalselectrical connection (cable, connector)housing cap


Figure 14, Incremental shaft encoder

AG: detection rid; PE: photo elements; TS: coded disc; ES: electrical signals;RM: reference mark; KL: ball bearing; MF: mounting flange; WL: shaft; KD:condensor

5.1.2 Coded disc

The core element of the encoder is the coded disc made of hardened andspecial surface-coated glass, see 4.2. DIADUR-. It is the carrier for thecircular graduations or gratings.Due to the special glass it is possible to operate the encoder also at hightemperatures without any major changes of the signal quality.

Increments On the outer edge of the coded disc there is the radial grid of lines and gaps(light and dark fields).These lines and gaps are called increments and they form the so-calledincremental track.

Measurement This incremental track forms the basis for the measurement of the encoder.With one complete revolution of the coded disc as many electrical signalsare transmitted as there are increments on the coded disc.The coded disc is fixed to a shaft which protrudes through the housing.

Figure 15, Coded disc with increments


5.1.3 Resolution - mechanical

The resolution is the number of physical light/dark fields on the coded discof the encoder which are provided as voltage pulses per revolution of thecoded disc.The mechanical resolution of an encoder cannot be modified.The number of increments on the coded disc depends on the resolutionrequired in the application.For standard units there is a large variety of different resolutions per type. Itusually starts with five and first continues in small steps, later the distancesincrease.

Standard resolutions The small incremental encoder RB for the voltage range of 10 � 30 VDC forexample is offered with the following resolutions in the ifm catalogue: 5,10, 20, 25, 30, 40, 50, 60, 100, 125, 150, 200, 250, 360, 400, 500, 600and 1,000.A different resolution always means a different encoder and thus a differentarticle/order number.The maximum resolution which can be shown optically as light � dark fieldsis 10,000 increments. The range of the resolution depends on the type.Resolutions deviating from the standard are available on request.

5.1.4 Signal generation

5.1.4.1 Through-beam method

The signals are generated by means of the through-beam method. Thethrough-beam method is the principle of photoelectric detection of finedetection grids. This detection principle can be compared to a miniaturisedphotoelectric through-beam sensor.

Figure 16, Photoelectric detection, through-beam method

KD: condensor; AG: detection grid; TS: coded disc; PE: photo elements; RM:reference mark.


5.1.4.2 Reference mark, zero index

The reference mark is on a second track next to the incremental track. Onceper revolution it generates a defined pulse, the so-called zero index, on aseparate channel.

5.1.4.3 Scanning plate

At a short distance opposite the rotatable coded disc with the incrementsthere is a fixed scanning plate. It has a grating on four fields and thereference mark graduating on a further field.

0°

180°

90°

270°Figure 17, Scanning plate, without reference mark grating

Grating period The four graduations of the scanning plate are shifted against each other byone-fourth of the grating period.One grating period = 360 degrees / resolution.The segments are adapted to the circle of the coded disc and therefore theyare slightly curved.

5.1.4.4 Condenser

All fields are penetrated by a parallel-orientated light beam which is emittedby a light unit consisting of an LED and a convex lens (condenser).

A

Lichtquelle

Figure 18, Light source and condenser

With one rotation of the coded disc the light is interrupted periodically bythe light and dark fields and its intensity is detected by silicon photo diodes.A photo element is assigned to each segment of the scanning plate.

5.1.4.5 Signal generation of the photo elements

Sine wave If a coded disc is rotated the photo elements for the incremental trackgenerate four sinusoidal current signals , each of which is electrically phase-shifted by 90 degrees.


0° 90°

180° 270°

0° 90°

180° 270°

0° 90°

180° 270°

0° 90°

180° 270°

0° 90°

180° 270°

I3

I1I2

I4

a b c d e

Figure 19, Sine wave of the photo elements

Sine curve I1: segment 0°Sine curve I2: segment 180°Sine curve I3: segment 90°Sine curve I4: segment 270°The photo element for the reference mark or the zero index generate asignal peak.The four sinusoidal photo-element signals are at first symmetrical to thezero line.

5.1.4.6 Photo elements

The photo elements are connected in push-pull circuit thus creating twooutput signals which are electrically phase-shifted by 90°.

3 4

1 2

Figure 20, Connection of the photo elements

DC component Due to the connection in push-pull circuit the DC component is suppressed.The DC component is generated by scattered light of the adjacent fields ofthe detection grid.

0° 90° 180° 270° 360°

I3-I4

I1-I2

Ie1

Ie2

Figure 21, Signal voltage


5.1.5 Pulse generation and analogue signals

5.1.5.1 Square-wave pulse trains

The sine curves Ie1 and Ie2 are converted into square-wave pulse trains bymeans of voltage comparators, thus generating two square-wave pulsetrains which are phase-shifted to each other by 90°.

Square-wave pulse train The square-wave pulse trains are amplified in the output stage of theencoder and provided as electrical signals in the form of voltage pulses.

0° 90° 180° 270° 360°

I3-I4

I1-I2

Ie1

Ie2

180°

180°90°

Figure 22, Pulse generation

90-degree-shift Due to the interaction of scanning plate and coded disc the electrical 90-degree shift from channel A to channel B has a mechanical origin. Thisensures that this shift remains the same for all rotational speeds of thecoded disc.For simple counting operations it would be sufficient to only evaluate oneoutput channel, but only by means of the second signal output which isshifted by 90 degrees it is possible to determine the direction of rotation orcounting (see 5.1.7).

5.1.5.2 Signal evaluation

As a standard an incremental shaft encoder provides three signal outputs:Channel A, channel B and channel 0 (zero index).


00

AA

BB

AS0

ASA

ASB

T0

TA

TB

V0

VA

VB

E0

EA

EB

UB

D

E

A

C

B

G

F

Figure 23, Signal generation, block diagram

A: shaft; B: scanning plate; C: coded disc; D: voltage supply; E: signaloutputs; AS0, ASA and ASB: signal output stages with inverted and non-inverted outputs; E0: infrared reception transistor; F: condenser; G: lightsource; T0: pulse generation (Schmitt-trigger); V0: direct-current amplifier.

The mark-to-space ratio of both output signals from channel A and channelB is 1 : 1 at all times.

Signal sequence The sequence of voltage levels of the output channels of an incrementalshaft encoder is as follows:

1. LOW level (voltage value zero).2. Voltage increase from LOW level to HIGH level (positive-going edge).3. HIGH level (voltage value of the operating voltage).4. Voltage drop from HIGH level to LOW level (negative-going edge).

If voltage is applied to the incremental shaft encoder it provides for eachchannel the level value which results from the position of the coded disc. Apossible voltage change of a channel from no voltage to operating voltagedoes not cause any counting operation in the subsequent evaluationelectronics.

5.1.5.3 Pulse diagram

The duration of the individual pulse (ON/OFF) depends on the rotationalspeed of the coded disc. Thus it is not possible to indicate a time for thepulse length.


180° 180°

90°

90°

A

B

NI

Figure 24, Pulse diagram channels A, B, and zero index (NI)

Therefore the duration of an individual pulse is fixed electrically to the value360 degrees.The ON pulse is present for the time of (electrically) 180 degrees, for theremaining 180 degrees the pulse has the value zero.The distance between channels A and B is electrically 90 degrees anddepends on the speed and direction of rotation of the coded disc.

Measuring step The measuring step is the angular value which results from the distancebetween two edges of the two square-wave pulse trains of output A andoutput B.Without previous interpolation of the measured signals the measuring stepcorresponds to the fourth part of the grating period (90 degrees) of theradial gratings.

5.1.5.4 Zero index, channel 0

The zero index, also called zero pulse or reference mark, is generated onlyonce per revolution of the coded disc. On the complete circumference ofthe index track there is only one segment.The position of the reference mark on the coded disc is also determinedmechanically.

As can be seen in figure 24 the relative duration of the HIGH level of thezero index is only half as long as that of channels A and B. Therefore theinput circuitry must have an input frequency for the evaluation of the zeroindex which is four times higher than for the evaluation of channels A andB. With a high number of revolutions of the encoder the length of the zeroindex is shortened. The distance between the edges becomes shorter. Incase of "slow" evaluation electronics/plcs this can lead to the signal notbeing detected even if the other channels can still be properly read.The zero index can be used to define a switch point, to count therevolutions or to synchronise a connected electronic counter.In addition to the mechanical position of the zero index on the coded discthe signal periods of channels A and B are used as reference values.

The standard zero index is 90° long � see figure 24.For the ifm type RB forthe voltage range of 10 to 30 V DC the length of the index is 360°.


180° 180°

A

B

NI

45°

360°

Figure 25, Zero index 360 degrees long (NI), type RB, 10 � 30 V

Reference mark outside To facilitate the determination of the zero index its approximate position ismarked by a reference mark on the outside of some encoder types. For thispurpose there is an indentation on the flange near the shaft. The sameindentation is also on the front of the shaft.If both indentations are matched, the signal for the zero index is present onthe output. For high resolutions the zero index is short and thereforemanual positioning is difficult.

5.1.5.5 Inverted output signals

For different encoders the three standard output signals (channels A, B andzero index)are additionally provided in the inverted state.The encoder then has six signal outputs in total: channel A and channel A-negated1; channel B and channel B-negated as well as zero index and zeroindex negated.

NI

NI

A

A

B

B

Figure 26, Pulse diagram with inverted channels (NI: Zero index)

Suppress interference Due to the inverted signals it is possible to evaluate the voltage difference.Thus parasitic signals on long connect ion cables have almost no negativeeffect.Except for types RA and RB all HTL2 shaft encoders provide the invertedsignals.

1 An expression like 'A-negated' is represented as an individual character or word by a line above thecharacter or word (see Figure 26).2 HTL stands for high transistor logic. These are units with an operating voltage higher than 5 V DC.


5.1.5.6 Sinusoidal signals

For some incremental shaft encoders the sinusoidal voltages instead of thesquare-wave pulse trains are provided for the channels A and B. They canbe processed in various ways in the input circuitry.These two sinusoidal increment signals are also phase-shifted by 90 degrees.

0° 90° 180° 270° 360°

x

y 1Vss

Figure 27, Sinusoidal output signals (Vss = Vpp)

The reference mark signal for the zero index is also available in analogueform. The voltage step has a nearly triangular shape of approx. 0.5 V.

1 Volt peak-peak (Vpp) If sinusoidal voltage signals are provided the voltage level is 1 Volt frompeak to peak.Cable lengths of up to 150 m are possible.The sinusoidal output signals can be digitised in an input circuitry(comparator). They are specially suitable for pulse multiplication � seebelow. They can also be used with digital drives to monitor the rotationalspeed even with very slow movements.

5.1.6 Wiring of an incremental encoder

The individual cores are differentiated by their colours and they have thesame meaning for all incremental shaft encoders of ifm electronic. The coreswhich are available depend on the respective shaft encoder.Wiring of an incremental shaft encoder:

brown channel Agreen channel A inverted (A-negated)grey channel Bpink channel B inverted (B-negated)redzero indexblack zero index inverted (zero index negated)blue L+ (sensor)white 0 V (sensor)brown/green +Ub (L+)white/green Un (0 V)lilac interference signal (inverted)screen housing


5.1.6.1 Interference signal

Some encoders have an interference signal as additional signal output. Theinterference signal indicates malfunctions of the shaft encoder like forexample breakage of the supply cores, failure of the light source, soiling ofthe coded disc or the photo elements.A square-wave pulse train indicates the malfunction. If the wire for theinterference signal has a LOW level, there is a malfunction. If the level isHIGH the unit is operational.For cable units the connection core (lilac) must be insulated if theinterference signal is not used, in order to avoid any short circuits. Unlike forthe useful signals, the output driver for the interference signal is notprotected against short circuits.

5.1.7 Detection of the direction of rotation for thedirection of counting

The electrical 90-degree shift between channels A and B in connection withthe dynamic signal changes is used by the subsequent evaluation electronicslike programmable logic controllers (plcs) or electronic up/down counters todetermine the direction of counting.

Signal change The signal changes and signal states of channels A and B of the shaftencoder are decisive for the detection of the direction of rotation orcounting.If the shaft encoder stands still there is no signal change. Input circuitscannot (yet) decide which is the current direction of counting.If voltage is applied to shaft encoders and evaluation/display electronics asignal change can take place on one or more output channels, dependingon the position of the coded disc in the shaft encoder. However, this signalchange is suppressed as counting pulse by the evaluation electronicsbecause it was taken into account for the counting process before switchingoff the supply voltage.This ensures that the direction of counting is correctly determined when themeasuring system is switched on and the coded disc starts moving.If the coded disc moves the positive signal change of channel A comesbefore the positive signal change of channel B and vice versa, depending onthe mechanical direction of rotation.

A

BFigure 28, Signal change

Phase discriminator The direction of rotation can easily be detected by means of a phasediscriminator in evaluation electronics by evaluating the phase position ofsignal A to signal B.


5.1.8 Pulse multiplication

Duplication By means of logic switching elements like AND and OR gates the rising andfalling square-wave pulse trains of channels A and B can be connected insuch a way that the output signals have a higher resolution than the onedetermined by the mechanical division of the coded disc.Due to the electrical processing times of the required logic gates it is notpossible to increase the number of pulses to any number in this case.

A

B

&

&

>1_BA

BA

Figure 29, Duplication of the pulses

The circuitry from figure 29 can also be implemented with an exclusive-OR-gate (XOR).Due to the pulse multiplication with logic gates the electrical 90-degree shiftof channels A and B is lost.If the 90-degree shift is required it makes sense to use a shaft encoder withsinusoidal output signals � see above.

Multiplication (logic gates) A further pulse multiplicat ion is possible with the respective electronics.

A

B

X1

X2

X3

X4

Figure 30, Pulse multiplication


Depending on which edge of a channel is evaluated the pulse trains shownin figure 30 and the related pulse multiplication can be implemented.

Single evaluation Pulse train X1 represents a single evaluation. A reaction to the to the fallingedge of channel A takes place. The number of pulses has not increased.

Double evaluation Pulse train X2 is generated if there is a reaction both to the rising edge andto the falling edge of channel A. It is a double evaluation with doublesymmetrical number of pulses.

Triple evaluation A triple evaluation is shown in the pulse diagram X3. In addition to therising and falling edges of channel A it also evaluates the rising edge ofchannel B. The pulse evaluation is triple, but asymmetric.

Quadruple evaluation Diagram X4 shows a quadrupl e evaluation. The rising and the falling edgesof both channels are evaluated. The number of pulses has quadrupled and itis symmetrical.

In the limit ranges wrong pulses may occur. The phase position of thechannels must be observed exactly. The pulse length after the multiplicationis to be set in such a way that with maximum rotational speed the newlygenerated pulses are about half as long as the original pulses of the outputchannels. The short signal duration resulting from this causes higherrequirements as regards the electronics of the evaluation unit (plc orcounter).

Multiplication from sinusoidal signals For shaft encoders which generate sinusoidal signals of 1 V pp , a multiplenumber of the mechanical resolution can be achieved (factor 10 and more)by means of linear interpolation.Pulse multiplication with sinusoidal signals as a basis has the advantage ofthe electrical 90-degree shift between the output channels A and B beingmaintained.

5.2 Absolute shaft encodersAbsolute measuring systems determine the current absolute position of themeasuring system in the form of clear code information by scanning thecoded disc. They signal this position to the subsequent electronics as codedvalue in binary form.The special advantage is that this position value is available unchangedafter a power failure. The exact position is also indicated if the encoder hascontinued to turn when no power was available.Wrong measurements due to wrong pulses and errors which add up aremostly excluded.

Binary numerical values Absolute shaft encoders convert rotational movements or positions intobinary numerical values. Each angular position of the coded disc is providedas a binary numerical value.Binary figures consist of individual bits which can only take the values 1 or0. For absolute shaft encoders the digital value 1 means that the level ofthe signal wire is HIGH. Therefore the digital value 0 corresponds to theLOW level.With their HIGH and LOW levels all signal outputs of absolute shaftencoders form a clear binary number. The prerequisite is of course that thesignal wires are in the correct order corresponding to their value.The binary numerical value of an absolute shaft encoder consists of up to 13bits. For each bit a separate signal wire is required.Angular positions, movements and posit ions can be determined by meansof the binary numerical value.


Figure 31, Coded discs

Many tracks In contrast to incremental shaft encoders the coded disc of absolute shaftencoders has considerably more tracks (see figure 31).The graduation carrier of absolute shaft encoders consists of a coded discmade of glass with several code tracks. Each individual track corresponds toone bit within the binary output value � see above.These absolute shaft encoders also work according to the principle of thephotoelectric detection of graduations.Transparent and non-transparent zones are distributed in concentric circles(= tracks)on the coded disc. On a fixed radial reading zone (photoelectricsensors detect the tracks)an exactly determined sequence of light � darkfields results from each position of the disc.One or several scanning plates are arranged at a short distance to therotatable coded disc. They have scanning fields which are assigned to thecoded tracks.A light beam aligned in parallel illuminates each scanning plate. This lightbeam is generated by an LED and a capacitor like in the case of theincremental shaft encoder.With the rotation of the coded disc the light beam is modulated and itsintensity is detected by the silicon photo elements.

Incremental signals For absolute shaft encoders which additionally provide incremental signalsfour scanning fields are assigned to the finest track.The four graduations of the scanning fi elds are shifted against each other byone fourth of the grating period like in the case of the incremental shaftencoders.


Figure 32, Photoelectric detection, through-beam method

LQ: light source; KD: condensor; TS: coded disc; PE: photo elements; AG:scanning plate.

If voltage is applied to the absolute shaft encoder, the binary value which iscaused by the current position of the coded disc is immediately provided atthe output channels in the form of HIGH/LOW levels.The number of tracks depends on the requested resolution, the distributionof the light and dark segments on the type of coding selected.Absolute shaft encoders are differentiated as follows:

Singleturn shaft encodersMultiturn shaft encoders

5.2.1 Resolution

The resolution of absolute shaft encoders depends on the number of tracks.Singleturn shaft encoders are available with resolutions of 256 (8 bits), 360,512 (9 bits), 1,024 (10 bits), 2,048 (11 bits), 4,096 (12 bits), and 8,192 (13bits). See also chapter 5.2.4 Coding.Multiturn shaft encoders have up to 13 tracks and thus a resolution of8,192 steps per revolution with 4,096 (12 bits) countable revolutions.

5.2.2 Singleturn shaft encoders

Singleturn shaft encoders are absolute shaft encoders. In contrast to theincremental units they provide a coded numerical value for each angularposition.After each complete revolution of the axle the numerical value starts withthe start value again.If the rotational direction of the shaft changes the counting direction of theoutput value changes as well.

Parallel data output Most singleturn shaft encoders have a parallel data output where each trackof the coded disc is assigned a separate data wire. Therefore the number ofconnection cores to be wired is very high.


Enable signal The data of the signal tracks are permanently provided by the shaft encoderif there is a LOW signal or no voltage on the release channels A and B. If aHIGH signal is applied to the release channels all signal outputs are of highimpedance and thus they are blocked.

Figure 33, Pulse diagram of the parallel interface

The signal outputs are assigned to two release channels � see figure 33.Thenumber of tracks for the respective release channel is as follows:

Release channel A: tracks 3 to 10 8, 9 and 10-bit shaft encoderstracks 7 to 12 11 and 12-bit shaft encoders

Release channel B: tracks 1 to 2 8, 9 and 10-bit shaft encoderstracks 1 to 6 11 and 12-bit shaft encoders.

LSB and MSB Track 1 is the least significant bit (LSB), the last track with the highest indexnumber (e.g. bit 12) is the most significant bit (MSB).If bit 1 (LSB) is not transmitted, the transmission error is smallest; if the lastbit (MSB) is not transmitted, the error is largest.The designation of the connections as regards the core colours variesdepending on the number of bits.Connection of a 10-bit shaft encoder:

brown Ub, plus, 10 - 30 V DCyellow/brown sensor, plus, 10 - 30 V DCwhite Ub, minus, 0 Vwhite/yellow sensor, minus, 0 Vgreen release channel Ayellow release channel Bwhite/grey bit 10 (MSB)white/green bit 9red/blue bit 8grey/pink bit 7lilac bit 6black bit 5red bit 4blue bit 3pink bit 2grey bit 1 (LSB)

The respective connection is indicated on each shaft encoder.


Multiplex operation Due to the fact that the signal outputs are of high impedance because ofthe LOW signal at the release channel it is possible to switch the outputsignals in parallel with other shaft encoders. Therefore a plc for example canoperate several shaft encoders with the multiplex method.In that case two or more shaft encoders are wired in parallel on the samechannels of the plc input card. Thus only 10 input channels are used for 10-bit shaft encoders, irrespective of the number of encoders. The releasechannels of the shaft encoders are triggered by means of the plc outputs.To do this two output channels per shaft encoder are required. The signaloutputs of the individual shaft encoders are read by the plc during operationeither one after the other or on demand. It is important that only one shaftencoder at a time is enabled.Depending on the version of the shaft encoder either TTL signals or 24 V DCsignals are provided.

Direction of rotation and counting With shaft encoders it must be possible to differentiate the direction ofrotation. Therefore it has been determined that the direction of rotation isalways indicated looking at the front of the shaft of the encoder.For the singleturn shaft encoder this means that rotation to the right isclockwise if you look at the shaft.In that case the direction of counting is ascending.

Direction of rotation clockwisecounting upDirection of rotation counter-clockwise counting down

5.2.3 Multiturn shaft encoders

Multiturn shaft encoders are also absolute shaft encoders. Like thesingleturn shaft encoders they prov ide a coded numerical value for eachangular position of the axle.Multiturn shaft encoders have the same design for determining the positionwithin one revolution as singleturn shaft encoders.In addition the number of completed revolutions of the axle is provided in afurther bit combination.In order to distinguish between the number of revolutions permanentmagnets embedded in the discs are used which are connected to each othervia gears for gear reduction.Detection is made via digital Hall-effect sensors.

Figure 34, Gear box with coded discs and Hall elements

HE: Hall element; CS: coded disc; GB: gear box.


The following diagram shows the pulse characteristics taking the example ofa (non-existent) multiturn shaft encoder with four bits for single turn andthree bits for multiturn.

015

015

015

015

015

015

015

015

015

0

15

0

0 1 2 3 4 5 6 7 0 1 x

y

Multiturn 0 - 7

Singleturn0 - 15

Figure 35, Multiturn encoder, 4 bits singleturn, 3 bits multiturn

5.2.4 Code types

In control technology different types of code are used, e.g. Gray code, BCDcode or dual code as well as different variants.

5.2.4.1 Dual code (binary code)

With the dual code (binary) code each digit is assigned a certain value,starting with 20 for the least significant position and 2n-1 for the mostsignificant position.The dual code can easily be processed from the technical point of view.The optical detection, however, can lead to reading errors as the bit changeof several tracks is not carried out exactly time-synchronously or becausethere is a bit change on several tracks at the same time (see figure 36,values 7 and 8). This can lead to wrong allocations of the position.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Bit 1 (LSB)

Bit 2

Bit 3

Bit 4 (MSB)

Value 0

Figure 36, Dual code


5.2.4.2 BCD code

The BCD code has a tetradic design. Each digit of a decimal number isassigned a 4-digit dual figure (tetrad). The BCD code is mainly used ifdecimal displays are to be triggered directly.Four bits allow numerical values from 0 to 15. For the BCD coding the bitsfrom (binary) 0000 to I00I are required. The bit combinations of I0I0 to IIIIare not required because they represent the decimal numbers 10 to 15.Therefore the efficiency of this code is not so high.The figure 3600 is shown as follows:

3 6 0 00011 0110 0000 0000

Thus at least 14 bits are required because the two preceding zeros of the bitcombination are not required for the three.The genuine binary code as well as the Gray code only need 12 bits for thesame figure. 212 = 4,096 (211 = 2,048).

5.2.4.3 Gray code

Absolute shaft encoders often use the Gray code. The advantage is itssimple design: It is mirror symmetric and proceeds by one step, i.e. whengoing from one position (number) to the next only one single bit changes.This minimises the risk of possible reading errors during transmission andfurther processing.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Bit 1 (LSB)

Bit 2

Bit 3

Bit 4 (MSB)

Value 0

Figure 37, Gray code

A 4-digit code results in 24 = 16 combinations. As the genuine Gray codecounts from 0 to 2n-1 these are the numbers 0 to 15 in the figure above.A 12-digit code (212 = 4,096 combinations) performs a decimal count from0 to 4,095.The bit information read with the Gray code is converted into a binary codeby means of a suitable code converter. It can then be further processed. Forfurther processing of the signals code converters (e.g. code converter Graycode � dual code) or program modules in programmable controllers can beused.

Reflectible Gray code The code values are provided in ascending direction if the shaft of theencoder turns clockwise. As the Gray code is reflectible descending codevalues can be generated as well with clockwise rotation of the shaft byinverting the most significant bit (MSB).


5.2.4.4 Symmetrically cut Gray code (Gray excess code)

The Gray code proceeding by one step is for resolutions which can berepresented as the power of 2 (2, 4, 8, 16,... 256, 512 etc.).If other resolutions, e.g. 360 or 1000 are to be implemented, the sectioncorresponding to the requested even-numbered area is taken from the Graycode � see figure 38 for the value 10. This ensures that the code proceedsby one step.However, the represented section does not start at zero anymore, but it is shifted by a certain amount.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Bit 1 (LSB)

Bit 2

Bit 3

Bit 4 (MSB)

Value 0

1 2 3 4 5 6 7 8 90

Gray Excess 10 Code

Bit 1 (LSB)

Bit 2

Bit 3

Bit 4 (MSB)

Value

Figure 38, Gray excess code

For the evaluation half of the difference between the original resolution andthe reduced resolution is deducted from the generated binary value.Calculation for determining the start value for example with the value 360:

1. The next higher binary value above 360 is 512 (29).2. The number 360 is deducted from this value, the result is 152.3. This is divided by 2; the result is 76.

The range of numbers starts at 76 and ends at 435. This range from 76 to435 is shown on the coded disc. The value 76 is converted internally andprovided as zero. Accordingly, the internal value 435 is provided as 359.


A511 0

76435

256

Figure 39, Cut Gray code for the value 360

The designation for the code shown in figure 39 is:512 Gray excess 76 code.With the mechanical resolution only even numbers are possible for the cutGray code � like for the normal Gray code.The cut Gray code (also called "reduced Gray code", e.g. 10 Gray excess 3code) is used if the advantages of a code proceeding by one step are to beused but if resolutions are required which do not correspond to a power of2. When choosing the resolution it has to be considered that the value canbe divided by 2 without any remaining fraction.Other resolutions result in the following positions:

76 to 436 with a required resolution of 360152 to 872 with a resolution of 720 and12 to 1,012 with a resolution of 1,000.

With the Gray code or cut Gray code the individual bits have no value, likefor example with the dual code where each bit combination is directlyassigned a decimal number by the power of 2.

5.2.4.5 Decadic Gray excess-3-code

This is a combination of the BCD code and the Gray code.Each individual decade is coded in the Gray code in such a way that itcounts up to the number 13 starting with the number 3. Following that thesecond decade starts with the number 3 and the first decade counts downetc.The decimal Gray excess-3-code is a code proceeding by one step and it ismirror-symmetric.A disadvantage is that the conversion is very complex from the point of viewof the hardware as well as from the point of view of the software.


5.2.4.6 Comparison of different code types

E D C B A0123456789

1011

1312

141516171819202122232425262728293031

E D C B A0123456789

1011

1312

141516171819202122232425262728293031

D C B A0123456789

D C B A0123456789

Decadic Gray-excess-3-Code

BCD- Code

Dual- Code Gray- Code

Figure 40, Code types

The table shows that only the Gray code and the dual code fully use allpossibilities, i.e. there are 2n combinations. With the Gray excess code thereare bit combinations which cannot be used.

5.3 Comparison of absolute shaft encoders andincremental shaft encoders

Absolute shaft encoders provide the actual position value immediately afterthey are switched on or after a power failure.Multiturn shaft encoders can in addition detect the number of revolutions.Thus these absolute shaft encoders have a very wide measuring range.With incremental shaft encoders on the other hand the plant would maybehave be set manually to the basic position or to a reference point.The complexity as regards connection and evaluation is higher for absoluteshaft encoders than for incremental shaft encoders. Absolute shaft encodersare also more expensive.


5.4 Data transmissionAs mentioned before absolute shaft encoders provide a data word thelength of which depends on the resolution. If there is a separate signaloutput for each track this is called parallel data transmission.

Many cores In order to transmit the information to the evaluation unit a cable whichprovides one core for each channel has to be laid. For a multiturn shaftencoder with 12 bits for singleturn and 12 bits for multiturn this wouldresult in 24 cores for the data cable.The respective number of signal inputs is also required at the evaluationelectronics, e.g. a plc. With high-re solution units this leads to the well-known wiring problems:

high susceptibility to interference,high cable costs,high installation complexity,thick, inflexible cables.

For singleturn shaft encoders with a maximum of 13 bits data thiscomplexity can still be justified. In this case parallel data transmission is stilloften used.With the 5 V unit multiplex operation with 8 and 4 channels is also possible.This does not reduce the cabling, but inputs on the evaluation unit or theplc.

5.4.1 SSI interface on the shaft encoder

A multiturn shaft encoder can detect 4,096 revolutions (12 bits) with aresolution of 8,192 steps (13 bits). If these data were to be transmitted inparallel 12 + 13 = 25 data wires would be required and in addition thewires for the voltage supply and the sensor.

Figure 41, SSI interface unit RM

Few cores Therefore serial data transmission is offered for multiturn shaft encoders.For this purpose the unit has an SSI interface (synchronous-serial interfaceEIA RS422A or RS485). Only four data cores are required for the datatransmission.In contrast to the parallel interface this one requires fewer components andit is less susceptible to interference. Considerably fewer wires than with theparallel interface are needed for the transmission. Furthermore considerablylonger cables are possible.These shaft encoders have the following connections in addition to thevoltage supply and sensor monitoring:


Clock and clock invertedTTL-compatible signals for data and data invertedTwo sinusoidal increment signals (A and B), 1 Vpp

Independent of the unit the data are transmitted either in the dual code orin the Gray code.

Figure 42, SSI, pulse diagram for singleturn shaft encoders

Figure 43, SSI, pulse diagram for multiturn shaft encoders

The times for T, t1 and t2 shown in the diagrams above must be observed.They are:

Clock T: 0.9 µs to 11 µst1: greater than 0.45 µst2: max. 0.4 µs.

Function In quiescent condition the clock and data wires are HIGH. The clock isgenerated by the evaluation electronics (e.g. SSI controller). The first fallingclock edge signals the start of the data transmission � the current measuredvalue is stored.Data transfer is carried out with the first rising clock edge. With thefollowing rising clock edges the data are transmitted bit by bit, starting withthe MSB. The transmission of a complete data word requires n + 1 risingclock edges (n = resolution in bits). Thus 25 clock edges are required for a24-bit shaft encoder.After the transmission of a complete data word the data output remainsLOW and the clock output remains HIGH until the shaft encoder is ready totransmit the next measured value (t3 � see figure 43).If during this time there is a new request for data output (clock) the datawhich have already been provided are provided again.In this case the data output is LOW between the LSB of the first datatransmission and the MSB of the second data transmission.


If the data output is interrupted (clock = high for t >= t3) a new measuredvalue is stored with the next clock edge.The input circuitry reads the data with the rising clock edge.The standard signal length is 25 bits (without parity bit), but a version with24 bits (or with parity bit) is available on request.In addition to the values for the absolute position incremental data can betransmitted as a sine wave in parallel.

360° el.

90° el.

A 0B 0

A

B

CFigure 44, SSI interface, incremental signal shape

The size of the incremental signals is 1 Vpp for a terminating resistor ofapproximately 120 . The signals for the channels A and B are almostsinusoidal and are also shifted by 90 degrees.The number of increments is limited to 512 per revolution.The evaluation of the serial data of multiturn shaft encoders can be carriedout by subsequent electronics � the SSI controller.

serial parallel

24 V DC

multiturnRM plc

+ –

power supply

SSIcontroller

Figure 45, SSI interface, block diagram

The data are updated synchronously with the readout cycle. Thus the dataare as current as the time distance between two readouts. Therefore aperiodic readout of the shaft encoder is recommended.After a longer readout break and simultaneous rotation of the encodershaft the data content of the first readout may be obsolete and should beignored.Connection of a multiturn shaft encoder with SSI interface:


black n. c. (not connected)red n. c.green n. c.brown n. c.brown Ub, plus, 10 - 30 V DClilac clockyellow clock - negatedwhite/green Ub, minus, 0 Vscreen housingblue/black channel B (+)red/black channel B (-)grey data - negatedgreen/black channel A (+)yellow/black channel A (-)pink data

5.4.2 SSI interface programming via software

Different multiturn shaft encoders with SSI interface can be parameterisedvia PC (ifm types RM6110 and RM6113). The required programming of theshaft encoder is carried out with a special software via a standard PC.The programming software is for programming as well as for checking theset values. This is especially necessary if units are replaced.

Figure 46, SSI programming software

Before setting up new or replaced programmable shaft encoders the correctsetting always has to be checked. If the factory setting remains unchangedthis may cause serious malfunctions of the plant.


Figure 47, SSI programming software, connection

The programming cable which is available as accessory connects the shaftencoder directly with the COM interface of the PC and serves for voltagesupply if the shaft encoder has not yet been connected to a controller/plc.The setting possibilities and operation of the software are very extensive andcan be found in the detailed operating instructions supplied with theproducts.The following features can be set/programmed for example:

Output format of the position values in dual or Gray codeTransmission format of the data in a triangular structure (SSI) or

synchronous-serial right-justified (see chapter 18.2 Glossary of technicalterms).

Direction of rotation for ascending position values.Singleturn resolution up to max. 8,192 positions per revolution.Multiturn resolution up to max. 4,096 distinguishable revolutions.Offset and preset values.

It is also possible to check the shaft encoder by means of the software.

5.4.3 SSI controller

The SSI controller enables the connection of absolute shaft encoders withSSI interface to a plc.

+5V R1

C1

R2

C2+5V

R2 R1

C1C2

R2

R2

R1

R1

C1C1 clock +

clock -

data +data -

linedriver

shaft encoder evaluation electronics

Figure 48, SSI interface, circuit example


The controller converts the serially transmitted Gray-coded data word of theshaft encoder into parallel binary or BCD-coded information.In addition it provides the following functions:

Monitoring function for voltage errors,Transmission errors (wire break) and incorrect operationVirtual zero point, i.e. the zero point can be defined new at anypositionScaling factors, i.e. the number of steps, the resolution, can be freelyselected between 1 and 4096, the number of revolutions can beselected between 1 and 4096 by duplicating, thus 2, 4, 8, 16,....The direction of rotation can be inverted.Code type, i.e. a choice between BCD and Hex code.Parity, i.e. a choice between an encoder with or without parity bit.

Figure 49, SSI controller

The pulse frequency for absolute shaft encoders is 100 kHz. The datafrequency for binary coded data is 1 kHz, 0.6 kHz in the BCD code.

LSB

D 00 D 01 D 02 D 03 D 04 D 05 D 06 D 07 D 08 D 09 D 10 D 11 D 12 D 13 D 14 D 15 D 16 D 17 D 18 D 19 D 20 D 21 D 22

LSB

T TD DUN UP-SOENSTR

24 VDAV PYB D 30 D 29 D 28 D 27 D 26 D 25 D 24 D 23

SSI-encoder-input

RSTn.c. n.c.

outputssingleturn

outputsmultiturn

outputsmultiturnsupply

Figure 50, SSI controller, connections

Outputs D00 - D15 for singleturn:

D00 (=LSB) to D11 (=MSB) with output in binary codeD00 (=LSB) to D15 (=MSB) with output in BCD code

Outputs D16 - D30 for multiturn:

D16 (=LSB) to D27 (=MSB) with output in binary code


D16 (=LSB) to D30 (=MSB) with output in BCD code

STR (strobe) input for the signal to call the current encoder value. With aHIGH-LOW edge to STR the last complete encoder value in theoutput buffer is provided to the plc.

RST (reset) input for external setting of the zero position.OEN (output enable) input for external switching signal which releases or

blocks the data outputs (for the use of several controllers on oneplc). HIGH releases the data outputs, LOW blocks them. If this inputis not connected to the plc the data outputs are permanently free.

DAV (Data-valid) If the strobe signal calls the data, these data are valid ifthe output DAV is HIGH. In case of a LOW signal the followingerrors might have occurred:

Transmission error of the SSI moduleMeasured values above the programmed resolution

PYB (output for the internal parity information) The parity is formedfrom singleturn and multiturn by means of the complete data word.In case of an even sum of all HIGH outputs including the parityoutput this output is HIGH.

5.4.4 Profibus-DP interface

Profibus is a further alternative to avoid having to use many cores for datatransmission of a multiturn or singleturn shaft encoder.

Figure 51, Profibus DP shaft encoder, type RM

Instead of an SSI interface or parallel outputs the shaft encoder has aninterface for Profibus DP. The shaft encoder operates as a slave alongsideother components on the bus. The expression "DP" stands for decentralizedperipherals.Profibus is a manufacturer-independent, open fieldbus standard determinedby the international standards EN 50170 and EN 50254.Profibus enables the communication of units of different manufacturers.It is suited for time-critical applications as well as for complex tasks. Furthertechnical and manufacturer- independent information is available on theinternet at http://www.profibus.com .


24 V DC

gateway shaftencoder

+ –powersupply

DP in

DP out

Figure 52, Profibus DP

Absolute shaft encoders with Profibus DP interface are distinguished by theircertification by the Profibus user organisation (PNO) and are thereforesuitable for unrestricted use in all Profibus DP networks.This means among other things that all possible baud rates, the completeaddress range and the unit characteristics are supported according to theProfibus unit profile for shaft encoders.The shaft encoder is configured in the Profibus system by means of the so-called device data base file (GSD) for MS Windows. The file can bedownloaded free of charge from the internet at http://www.ifm-electronic.com or http://www.profibus.com.The assignment of the addresses and the setting of the terminatingresistance are carried out on the unit. The address of the unit can be setfrom 3 to 126. It is not possible to set the address via the Profibus master.

B

0

5

0

5

A

AA BB

+Up-0 V

B/ABUS

B/ABUS

PROFIBUS- DP

Figure 53, Profibus, addressing and terminating resistor

The data are transmitted in the dual code. The programming interface has atransmission rate of max. 12 MBaud3.The programming possibilities according to the Profibus profile for shaftencoders class 2 are for example:

3 MBaud = megabaud


counting direction of the code valuesresolutionzero pointlimit position HI and LOmotion indicationseparation multiturn and singleturn shaft encoder

Furthermore the following diagnostic possibilities according to the Profibusshaft encoder profile class 2 are available:

alarmswarningsstatusserial number of the shaft encoder.

Manual A comprehensive manual is supplied with the unit. It describes theinstallation and configuration possibilities.These are for example:

General information about the Profibus technology.Unit installation as regards cabling, addressing, terminating resistor andGSD file.Unit configuration consisting of encoder class, operating parameters,data exchange, diagnostic information.Configuration of the DP-Profibus encoder on a Siemens plc type S7-CPU 315-2 DP, version STEP7 V5.X.

5.5 Accuracy of the shaft encoderThere are three types of accuracy as regards a shaft encoder:

dividing errormark to space ratiophase difference

The accuracy of a shaft encoder is indicated in electrical degrees or as partof the grating period.The accuracy of the provided signal sequence of a shaft encoder mainlydepends on the following conditions:

1. Error of the radial gratings of the coded disc.2. Error in the grating of the detection grid.3. Eccentricity of the coded disc to the shaft.4. Radial runout of the bearing.5. Deviations due to the coupling with rotor couplings (solid shaft

encoder).6. Interpolation error during further processing of the measured signals.


5.5.1 Dividing error

The dividing error is described as a deviation of any edge to its exactgeometric position. It indicates the greatest deviation of the nominaldistance between two pulse edges of one or several pulse channels. Thedividing error consists of a mechanical rotational error and the electronicrepeatability.It does not add up with several revolutions of the shaft encoder.The dividing error is very important with positioning applications which areto be carried out during one revolution of the shaft encoder.

5.5.2 Mark-to-space ratio

The mark-to-space ratio describes the ratio between the rising and thefalling pulse edges. It is important for the calculation of the actually requiredlimit input frequency of the input circuit of the evaluation electronics. Theaccuracy value is indicated for each shaft encoder.

A

360°

Figure 54, Mark-to-space ratio

Range A in Figure 54 indicates the location of the variation range.

5.5.3 Phase difference

The phase difference describes the variation of two subsequent edges of thetwo channels A and B by their nominal distance. This distance is to be 90degrees electrically. The maximum possible deviation is indicated in the datasheet.

A90°

360°

Figure 55, Phase difference

The area A in figure 58 indicates the variation range. For resolutions up to5,000 the accuracy is ± 1/20 grating period. This is also valid for a detectionfrequency of one to two kHz and at room temperature.


If the resolution is above 5,000 the accuracy is indicated in angular seconds.It is approximately ± 12 angular seconds.The accuracy of the absolute position values is indicated in the technicaldata sheet of the respective unit.


6 Mechanical designShaft encoders are differentiated as regards their type of mechanicalcoupling. There are solid shaft encoders and hollow shaft encoders withdifferent types of flange for mechanical fixing.For the electrical connection there are cable units and connector units, inexceptional cases also units with terminal chamber (e.g. absolute shaftencoder type RM for Profibus connection).

6.1 Solid shaft encodersSolid shaft encoders are coupled to the machine by means of shafts with adiameter of 6 mm or 10 mm and the respective mechanical couplings. Thecoupling has to compensate for the vibrations and shocks from themachine.

Figure 56, Solid shaft encoder

The shaft at the end of which the coded disc is mounted inside the shaftencoder, is guided by two ball bearings.

Ball bearing Depending of the flange size the shafts are in most cases designed in such away that the same ball bearings can be used for different shaft diameters.The diameter of the shaft in the ball bearing is 10 mm, but outside the shaftonly has a diameter of 6 mm.The shaft encoder has two ball bearings positioned behind each other onthe shaft in the flange. The ball bearings are closed in order to meet therespective protection rating, i.e. the balls cannot be seen from outside.There is an additional seal in front of the ball bearing.If the mounting tolerances and the maximum rotational speed are observedthe ball bearings have an average lifetime of between 25,000 and 120,000operating hours.


Figure 57, Ball bearing (K) with sealing ring (D)

The ball bearings are particularly important because their mechanical designis decisive for the smooth running of the shaft.This is especially interesting in cases where the drive for the encoder shaftdoes not have a high torque or if a high protection rating is required for theshaft encoder. For this reason the starting torque is indicated in the datasheet.

Starting torque It is the minimum impact on the shaft required to start a rotationalmovement of the shaft from standstill.The value of the starting torque is smaller than 1 Ncm (Newton centimetre)and it is indicated for room temperature.The flange is for the mechanical fixing of solid shaft encoders.

6.1.1 Flange types for solid shaft encoders

The flange The flange of a shaft encoder is a precise aluminium injection-moulded part.Outside it has the respective profile with the corresponding threaded blindholes for fixing.The inside is for the ball bearings for the shaft, for fixing the housing cap aswell as fixing and positioning the LEDs for the through-beam method.

G

Figure 58, Flange with threaded holes (G)


The units are distinguished by their individual flange versions. The followingflange types are standard:

1. Clamp flange2. Synchro flange3. Round flange

Figure 59, Flange types (1, 2, 3 � see above)

The diameter of the flange and the position of the mounting threads arestandardised.

Figure 60, Clamp, synchro and round flange

In addition to the flange types mentioned above there is also a squareflange.

6.2 Hollow shaft encodersHollow shaft encoders have their own bearing and a coupling at the statorside. They can be mounted directly on the machine without any specialcoupling.


Figure 61, Hollow shaft encoders

With an angular acceleration of the shaft the stator coupling must onlywithstand the torque resulting from the bearing friction. The special statorcoupling is the basis for a high natural frequency of the coupling andenables relatively high amplification in the control circuit. The coupling atthe stator side allows axial movements of the driving shaft.The maximum permissible axial movement is for types

RO ± 1 mmRA ± 0.5 mmRP ± 1.5 mm.

The mechanical connection to the shaft is established by tapping off thedrive. The hollow shaft of the encoder is put onto this shaft.Additional fixing possibilities on the housing ensure protection againstrotation and a secure fit of the housing.Due to the special patented bearing inside the shaft encoder vibrations arecompensated for.The hollow shaft versions differ depending on the encoder type. They canbe continuous or open on one side (blind hole).The dimensions of the hollow shaft are designed to fit common sizes veryprecisely. In most cases they have the tolerance H7 according to DIN ISO286 T2. Common dimensions for the inner diameter are:

6 mm (6 mm to 6.012 mm)20 mm (20 mm to 20.021 mm)50 mm (50 mm to 50.025 mm)


Figure 62, Hollow shaft encoder, cut-away view

The mounting of the hollow shaft on the shaft of the drive is carried out bymeans of one or two set screws (n) or a clamping ring.Depending on the type the driving shaft must protrude far enough into thehollow shaft (indication in the data sheet).The shaft of hollow shaft encoders is also only for the transmission of therotational movement.The use of hollow shaft encoders is cheaper in comparison with solid shaftencoders because additional couplings , mounting devices and other fixingcomponents are not needed. The required mounting space is smaller thanfor encoders with solid shaft.

6.2.1 Mounting of hollow shaft encoders

Hollow shaft encoders are mounted by means of a stator coupling.

Figure 63, Stator coupling for hollow shaft encoder


7 Electrical connectionThe electrical connection of shaft encoders can be carried out by means of aconnection cable or a connector.

7.1 Connection cableThe connection cable at the unit is one or two metres long. Cable lengths of10 m are also available. At the end of the cable a short section of theinsulation is stripped. The cores do not have any wire end ferrules.

Cable length If a plug and socket connection wi th a suitable extension lead (cross-section,screening) is used, a max. length of 100 m for the 5-V version and 50 m forthe 10 to 30 V version is possible.The cable material is polyurethane (PUR) or polyvinyl chloride (PVC),depending on the unit.The PUR cable is more resistant to oil, hydrolysis and microbes.

Bending radius The permissible bending radii of the connection cables generally depend onthe diameter and the material.Guide values for PUR cables with 5 or 6 mm and PVC cables with 5 or 8mm:

r 20 mm if flexed once,r 75 mm if flexed continuously.

Screening All connection cables of the shaft encoders are screened (metal meshscreening). The screen of the connection cable is fixed internally to thehousing cap. The individual connection cores are not screened.

Temperature ranges Depending on the cable version the encoder cables can be used in thefollowing temperature ranges:

for firmly laid cables -30° C to 85° C.for frequent flexing -10° C to 85° C.

If the cable has a restricted resistance to hydrolysis and microbes, it can beused at up to 100°C for stationary and moving applications.

R

A

Figure 64, Cable entry axial (A) and radial (R)

The cable entry at the unit can be axial or radial.


It is implemented by means of a cable gland in most cases. Small shaftencoders do not have a cable gland for reasons of space. In this case thecable entry is radial.

Figure 65, Cable entry for small units

The cable entry of a small encoder, like shown in figure 68, allows axial aswell as radial connection.Some shaft encoders have a connection cable with cable plug. These unitshave a cable with a plug mounted at the end.

Figure 66, Cable plug

7.2 ConnectorThe size of the connector on the unit, the number of pins and theirconnection depend on the unit version.


Figure 67, Connector unit

In many cases it is a 12-pole connection.

9 812

7

6

5114

3

2

101

Figure 68, Pin connection of a plug

The pin connection of the plug at the unit is described in detail in the datasheet.

7.2.1 Sockets/coupling

Suitable sockets for the connection of connector units are offered asaccessories.The data sheets of the shaft encoders with connector specify the type ofconnector so that the suitable sockets (coupling with cable) or the suitablecouplings for wiring can be selected from the ifm range of accessories.A typical designation for a connector is for example ifm 1001.2.

Figure 69, Coupling, electrical

The couplings are rated for operation with DC voltage and have a voltagerange of 4.5 V DC to 30 V DC. The temperature range is �40 degreesCelsius to +140 degrees Celsius. The couplings have the protection rating IP67. In many cases the housing material is brass with a plastic sheathing.


7.3 Laying the cableConnectors or terminal boxes with metal housing should be used formounting and no other signals should be led through these components.The housing of the encoder, connector, terminal box, and evaluationelectronics should be connected with each other via the screening of thecable.The screening should have as low an inductance as possible (short, largesurface) and must be connected in the area of the cable entry. Thescreening system as a whole must be connected to protective earth.The connection cables should be laid separately from any sources ofinterference (e.g. cables of motors, solenoid valves etc.) In general, aminimum spacing of 20 cm is sufficient.Connections or plugs should not be disconnected while live.

7.4 Earthing and screeningOn a cabled unit the screen is directly connected to the encoder housing.

A

Figure 70, Earthing and screening

The screen connected at the encoder should be led directly to the evaluationelectronics and be earthed there. This ensures the best possible screeningagainst interference from outside.


8 Mechanical dataShaft encoders are a combination of high-quality mechanics and electronics.With the respective design they can be considered as precise measuringinstruments. For this reason the mechanical data are very important.In principle, incremental and absolute shaft encoders have the samemechanical design. The individual components differ in detail. There aredifferences as regards the coded discs, the number of photo elements andthe internal evaluation electronics.

8.1 Maximum mechanical rotational speedThe maximum mechanical rotational speed indicated in the data sheet isstated for permanent operation at the highest temperature.It assumes that the connection between the driving shaft and the encoderhas no considerable offset.The maximum rotational speed of the complete system of encoder andevaluation electronics is influenced by three factors:

mechanical rotational speed of the shaft encoderlimit frequency/maximum output frequencymaximum input frequency of the evaluation electronics.

8.1.1 Mechanical rotational speed of the shaft encoder

The maximum permissible mechanical rotational speed is indicated in thedata sheet. It results from the mechanical load of the encoder. For mostunits it is between 10,000 and 12,000 revolutions per minute. Exceptionsare hollow shaft encoders with a maximum of 3,000 or 6,000 revolutionsper minute.

8.1.1.1 Limit frequency / maximum output frequency of the shaftencoder

This is an electrical value for the output stages of the shaft encoder � seebelow.The mechanical rotational speed and the maximum output frequency of thesignal outputs are in direct correlation with the number of pulses providedper revolution. This means that the rotational speed during operation mustnot exceed the maximum permissible mechanical rotational speed of theshaft encoder and that the rotational speed must not become so high that itexceeds the maximum permissible output frequency of the output stagebecause of the number of increments.Example:A shaft encoder has 5,000 increments per revolution and a maximumoutput frequency of 250,000 Hertz. Thus the shaft encoder may only beoperated with max. 50 revolutions per second (3,000 min-1) even if it is ratedfor 10,000 min-1 so that the maximum output frequency is not exceeded.


8.1.1.2 Maximum input frequency of the evaluation electronics

For the input electronics there are usually details about the maximumfrequency taking into account the number of signal edges to be evaluated.In case of pulse duplication or mult iplication the pulse length is reducedaccordingly. Furthermore the phase difference error must be taken intoaccount.The influences described above should be checked for the concreteapplication in order to determine the suitability of the shaft encoder. Due tothe tolerances a shaft encoder and evaluation electronics should be chosenwhich can process at least 1.5 times the frequency.

50

100

150

200

250

300

350

0 2000 4000 6000 8000 10000 12000rot. speed [min-1]

5000 pulses/rev. 2500 pulses/rev.

1000 pulses/rev.

500 pulses/rev.

250 pulses/rev.

Figure 71, Rotational speed and switching frequency

8.2 Shaft loadThe shaft of an encoder is made of stainless steel. The maximum mechanicalshaft load is indicated for the outer end of the shaft, i.e. the place with thehighest possible leverage.The load of the shaft influences the bearing. Indirectly the shaft load alwaysmeans the load of the bearing.

A

R

Figure 72, Shaft load, axial (A) and radial (R)

Typical values are:

axial 10 N (Newton), 20 N, 40 Nradial 20 N, 60 N.


Depending on the ball bearing The shaft load mainly depends on the design of the bearing. Small unitswith small ball bearings have lower values for the permissible load. Thevalues for each shaft encoder are indicated in the data sheet.

8.3 Shock resistance and vibration resistanceThe shock resistance indicates the highest permissible value of an impact orshock which may occur for a short time. For ifm units this value is 100 g fora time of 11 ms (g = gravitational acceleration); type RB is an exception,however. In this case the shock resistance is 30 g for 11 ms.

Acceleration To determine this value the units are connected and mounted according totheir specified use (e.g. by means of the fixing holes on the front of theflange). The units are tested in a drop-test machine by dropping them andbringing them to a gentle stop. The acceleration is 100 g (30 g for type RB).The amplitude at which vibration of the unit dies out (attenuation factor)must stop after 11 ms.Despite these high values impacts or shocks with a hammer etc., forexample for aligning the system during installation must be avoided.

Vibration A value is also indicated for vibrations at which the encoder does not showany malfunction or is not destroyed in continuous operation. For ifm unitsthis value is 10 g for the frequency range of 55 to 2,000 Hz.The acceleration values indicated in the technical data sheet of the shaftencoder do not impair the function of the units. They can reduce theaccuracy, however.

8.4 Housing materialAll shaft encoders have a metal housing. The shaft is made of stainless steel,the flange and the cap are made of aluminium.

8.5 Protection ratingifm shaft encoders are supplied with the protection rating IP 64 as astandard. This value refers to the shaft entry, not to the housing with cableentry or flange connector. For types RB, RC, RU, and RV the protectionrating IP 66 with an additional sealing of the shaft is available on request. Ithas to be taken into account that the units are slightly stiffer due to thespecially sealed bearings.The singleturn shaft encoders have IP 65.The housing (cap), the cable entry and the flange sockets meet therequirements of IP 67.

8.6 Operating temperatureShaft encoders may be used at operating temperatures starting at �30degrees Celsius up to +100 degrees Celsius. The temperature rangedepends on the type of unit.The operating temperature range indicates the limit temperatures of themounting environment at which the nominal technical data of the encodersare observed (DIN 32 878).Incremental shaft encoders with solid shaft have the widest temperaturerange. Hollow shaft encoders have the smallest temperature range.

Storage temperature Often the storage temperature is also indicated in the data sheet. This is theambient temperature during storage or transport of the unit in the box.


9 Electrical dataIn general the current consumption of the shaft encoder increases slightlyafter approx. 5 to 6 years � see below.

9.1 Voltage supplyIncremental and absolute shaft encoders are only operated with DC voltage.There are two versions:

1. TTL voltage range, 5 V DC ± 0.5 V and2. HTL voltage range, 10 V - 30 V including residual ripple.

After the transient condition of the supply voltage the tolerances indicatedhave to be observed.

Ub

t

Upp

4.75 V5.0 V

5.25 V

typ. 500 ms

Figure 73, Transient condition of the TTL voltage

Uss = Upp

Figure 73 shows that it can take up to 500 ms until the supply voltage iswithin the tolerances.

The voltage level of the output pulses depends on the supply voltage.Internal operating voltage The internal operating volt age of the shaft encoder is ensured by built-in

voltage regulators. The output pulses are not concerned by this.This means that operation of the shaft encoder is maintained even with apoor supply voltage (voltage dips, high residual ripple). The signal outputs,however, depend on the voltage characteristic of the supply voltage.The shape of the output pulses in case of poor supply voltage can lead tothe subsequent evaluation electronics not detecting all pulses.

Residual ripple The figure below shows that pulse 2 is below the HIGH level of thecontroller and can therefore not be detected/counted.

P

1 2 3Figure 74, Residual ripple of the signal outputs

For linear measurement the pieces to be measured become too long.


9.2 Voltage supply via the external evaluationelectronics

Many application systems consist of an electronic counter or anotherevaluation unit (e.g. speed monitor). In such cases the voltage supply of theshaft encoder is often carried out directly via an internal power supply of theevaluation unit (sensor supply).If this is the case it must be ensured that the performance of the powersupply of the evaluation electronics is capable of supplying the requiredenergy to the shaft encoder.If the evaluation unit does not provide sufficient power this can result in theproblems with the output pulses described above or the evaluationelectronics is damaged due to overload.

External power supply If the sensor supply of the evaluation unit is not sufficient an additionalexternal power supply must be used for the supply of the shaft encoder.When wiring the three units encoder (D), evaluation unit (A) and powersupply (N) it must be ensured that the power supply is not switched directlyin parallel to the sensor supply � see figure below.Such cases can lead to compensating currents flowing due to the differentinternal resistances of the two power supplies. This can damage one of theunits.

Reference level In all cases, however, the negati ve connections of all units involved have tobe connected to each other in order to get a common reference point.

- + - +

A B B A

Ub Ub

D N A

Figure 75, Encoder supply with external power supply

The output voltage of the power supply (N) should have the same level asthe sensor supply of the evaluation unit (A) and it should be within theoperating voltage range of the shaft encoder.

9.3 Sensor cables for encodersLong supply cables can lead to insufficient voltage supply of the shaftencoder due to the inherent resistance of the cables. Via the sensor cablesthe external electronics can detect the voltage at the encoder and adjust itby a suitable control unit if necessary.If the sensor cables are not needed, they can be connected in parallel withthe respective supply cable in order to reduce the voltage drop.The sensor cables are designated as 'sensor' in the data sheet and on thetype label.


9.4 Current consumptionThe current consumption of a shaft encoder consists of the current which isrequired for the actual operation of the shaft encoder (basic consumption)and the current which flows via the output stages of the shaft encoder tothe evaluation electronics.

Basic consumption The current consumption of a shaft encoder is not constant. It increaseswith time because the luminosity of the LED(s) has to be re-adjusted for thethrough-beam method and it depends of course on the number of pulseoutputs being triggered at the same time.The data sheet only indicates the current consumption which corresponds tothe basic consumption of the shaft encoder. These are typical values, e.g. 95mA (max. 150 mA). The value in brackets is the highest value for the currentconsumption. It can be reached if the LEDs have been re-adjusted up to thehighest value (see below).

Maximum current consumption Absolute shaft encoders have a higher current consumption thanincremental shaft encoders.In many cases only one value is indicated in the data sheet � the highestpossible value. When dimensioning a power supply the highest value for thecurrent consumption of the shaft encoder(s) should always be calculatedwith.

9.4.1 Light-emitting diodes (LEDs)

In the past miniature incandescent lamps were used in shaft encoders. Thelighting area of an incandescent lamp is larger than with LEDs and theluminosity does not decrease so much in the course of time as in the case ofLEDs.

Disadvantages of the incandescent lamp These incandescen t lamps generated white light. The luminous efficiencywas low in comparison to the power consumption; the susceptibility tofailure was high.

LED As the performance of LEDs increased considerably in the past they are nowbeing used in shaft encoders. For this purpose they are aged. This ageingensures that the luminosity does not decrease very much any more.In addition the luminosity of the LED is automatically re-adjustedelectronically if it ages nevertheless or if the coded disc is soiled.Therefore the current consumption of the unit increases with time.Due to the use of LEDs which are bigger and more luminous it has recentlybeen possible to illuminate all photo elements with only one LED and oneconvex lens (condenser).Therefore the advantages of the LED, i.e. low current consumption, long lifeand vibration-resistant operation can also be used in the design of shaftencoders.

9.5 Current rating of the signal outputsThe current rating of the signal outputs indicated in the data sheet alwaysrefers to one individual signal output.The standard maximum current rating is

20 mA for TTL output stages50 mA for HTL output stages.

For hollow shaft encoders there may be the exception that the HTL outputstage can only be rated with 20 mA.


This is similar for absolute shaft encoders with parallel signal outputs. In thiscase the maximum current rating per output is 20 mA, or 6 mA if there aremany signal wires.The output stages for the signal outputs of HTL shaft encoders are short-circuit protected. However, they are not protected against reverse voltages.The voltage supply of these shaft encoders is reverse-polarity protected, butthe signal outputs are not.

TTL without protection TTL shaft encoders are the most sensitive shaft encoders as regards wrongwiring. The signal outputs are not short-circuit protected and not protectedagainst reverse voltage and the supply voltage is not reverse-polarityprotected.The required protective functions, for example a reverse-polarity protectiondiode cannot be implemented because the minimum levels for TTL-operation might not be reached due to the voltage drops connected withthis.The HIGH level is above 2.5 V; the LOW level is below 0.7 V.

9.6 Signal frequency

9.6.1 Signal frequency and mechanical rotational speed

The current signal frequency for incremental shaft encoders results from theproduct of resolution and mechanical rotational speed. It must not exceedthe maximum possible switching frequency indicated in the data sheet inorder not to saturate the unit.Especially with shaft encoders with high resolutions it may happen that themaximum permissible switching frequency is exceeded, but not themaximum permissible mechanical rotational speed. Therefore it must bechecked in each application if the signal frequency to be expected is not toohigh.Evaluation electronics to which a shaft encoder is connected must of coursebe rated for the signal frequencies to be expected.The following diagram shows which rotational speed is permissible for agiven resolution.

500 1000 2000 5000 100001000

2000

5000

1000012000

50 kHz

300 kHz160 kHzY

X

Figure 76, Resolution and rotational speed

The x-axis in figure 76 shows the resolution, the y-axis the rotationalspeed.The designations of the three graphs show the maximum possibleoutput frequency of the output stage of the shaft encoder.


9.6.2 Signal frequency and cable length

If the cable length to the evaluation unit for units with TTL output stage isto be longer than 100 m it has to be taken into account that the maximumoutput frequency of the shaft encoder cannot be reached any more.In any case the supply voltage of 5 V DC at the shaft encoder should beensured. Via the sensor cables the external electronics can detect thevoltage at the encoder and adjust it by a suitable control unit if necessary.

y

x30

506080

100

150200

300

40

250

Figure 77, Cable length and output frequency, TTL

The x-axis in figure 77 shows the output frequency in kHz; the y-axis showsthe cable length in metres.

For shaft encoders with HTL-output stage there is an additionaldependence on the supply voltage:

y

x10122030506080

100120

200300

Up= 15 V

Up= 24 V

Up= 30 V

Figure 78, Cable length and output frequency, HTL

The x-axis in Figure 78 also shows the output frequency in kHz; the y-axisshows the cable length in metres.With decreasing supply voltage (Up) for the shaft encoder the maximumoutput frequency decreases as well.


10 Overview shaft encodersExperience has shown that the types offered as standard solutions aresufficient for most positioning problems.There is a choice of different units, depending on which resolution isrequired, which force is to be applied to the bearing of the shaft and howcable and connector entry are to be designed.

Incremental shaft encoders

Type ResolutionOperating

voltage(TTL/HTL)

Flange(type / Ø in

mm)

Shaft(Ø in mm)

Outputsignals

(optional)

Switchingfrequency in kHz

(TTL/HTL)

Max. rot.speed (min-1)

Optionconnector

RB 5 � 1,000 5 / 10 � 30 R / 36.5 6 TTL, HTL 300/160 10,000 yes

RC 40 � 512 5 / 10 � 30 R / 58.0 6 TTL, HTL 300/160 12,000 yes

RU 48 � 10,000 5 / 10 � 30 S / 58.0 6 TTL, HTL 300/160 12,000 yes

RV 50 � 3,600 5 / 10 � 30 K / 58.0 10 TTL, HTL 300/160 12,000 yes

RA 10 � 1,000 5 / 10 � 30 - / 36.5 6, open onone side

TTL, HTL 300/160 12,000 yes

RO 100 � 5,000 5 / 10 � 30 - / 58.0 10, open onone side TTL, HTL 300/160 12,000 yes

5 / - 20, open onone side

TTL 300 6,000 yesRP 1,000 � 3,600

- / 10 � 30- / 877.0

50, open onone side HTL 160 3,000 yes

Flange types: R = round flange; S = synchro flange, K = clamp flange. Shaft types: V = solid shaft; H = hollow shaft

Absolute shaft encoders

Type ResolutionOperating

voltage

Flange(type / Ø in

mm)

Shaft(type / Ø in

mm)

Outputsignals

(optional)

Incrementalsignals

Max. rot.speed (min-1)

Optionconnexctor

256 � 4,096parallel HTL / Gray no 10,000 yes

RN1,024 � 8,192

serial

10 � 30 S / 58 V / 10

SSI / Gray 1 Vpp / 512 12,000 yes

8,192 x 4,096serial 10 � 30 S / 58 V / 6 / 10 SSI / Gray 1 Vpp / 512 12,000 yes

max. 8,192 x 4,096serial, programmable

10 � 30 K / 58 V / 6 / 10 SSI / Gray 1 Vpp / 512 12,000 yes

max. 8,192 x 4,096programmable,

Profibus10 � 30 S / 58

K / 58V / 6 / 10 Profibus - 12,000 yes

RM

8,192serial 10 � 30 H / 58

H / 12(open on one

side)SSI / Gray 1 Vpp

/ 512 10,000 yes

Flange types: R = round flange; S = synchro flange, K = clamp flange. Shaft types: V = solid shaft; H = hollow shaft


11 Operating instructionsAll shaft encoders are supplied with detailed operating instructions.Observing the indicated conditions ensures permanent safe use of the unit.

Figure 79, Operating instructions, example

The operating instructions are available in several languages (German,English and French).


12 Data sheetThe data sheets of shaft encoders provide clear and nearly completeinformation about the technical data of a shaft encoder. In addition to theimportant data like article number, type designation, resolution, and outputfunction they contain a technical drawing, a pulse diagram and theconnecton.

Figure 80, Data sheet of the shaft encoder RV1009


Figure 81, Data sheet of the shaft encoder RM6001


13 AccessoriesShaft encoders can be mounted easily and operated safely with thecorresponding accessories. ifm offers a wide range of accessories.

13.1 Couplings for solid shaft encodersIncremental shaft encoders (types RC, RU and RV) have their own bearingrated for up to 60 N (radial at the shaft end) for speeds up to 6,000revolutions per minute. Due to this load capacity it is possible to mountthese encoders directly on mechanical transmission elements such astoothed wheels, frictional wheels or pulleys.If the encoders are subjected to higher strain, it is recommended to use acoupling for the shaft-side connection of the drive.The coupling compensates for production and mounting tolerances as wellas temperature influences and misalignment between encoder shaft anddriving shaft. Thus the bearing of the shaft encoder is not subjected to anyadditional external stress.The coupling has to meet high demands. It has to be designed in such away that it withstands the radial and axial forces and transmits therotational movement without any major delay.

Figure 82, Flexible coupling

While in the case of torsion-proof but flexible shaft couplings axial shaftdisplacement only generates static forces in the coupling, radial and angulardisplacement results in alternating stress, restoring forces and torques whichcan strain the shaft bearing of the encoder.There are three different alignment errors when mounting the couplings:


a

Figure 83, Axial, radial and angular displacement

The maximum permissible displacement is indicated in the data sheets ofthe couplings. Displacement types:

axial displacement : ± 0.4 mmradial displacement a: ± 0.25 mmangular displacement : ± 3.5 degrees.

These values are valid for 23°C room temperature. The values for radial,angular and axial displacement are maximum values which must not all bereached at the same time during operation.The life of a coupling depends on to what extent the permissible tolerancesare used.

Grub screw Couplings can be fixed by means of clamping screws or grub screws (setscrew with hexagon socket or slot).For clamping, the front faces of the coupling are slotted. The slot is pressedtogether on the shaft by means of a through bolt.The grub screws clamp directly onto the shaft. Depending on the material ofthe screw and the tightening torque indentations on the shaft may occur.Therefore couplings with grub screws for fixing are mainly used on shaftswith a flat.

Different axle diameters Often the hub bore holes in both front faces of the couplings have the samesize, e.g. 6 mm.There are also versions with different bore holes for a better adaptation tothe machine or to the drive. On one side of the coupling there is e.g. a 10-mm bore hole, on the other side a 6-mm bore hole.


Figure 84, Flexible coupling with different bore holes

In addition to the flexible coupling with its excellent mechanicalcharacteristics the spring disc coupling has a further advantage: it iselectrically isolating.

Figure 85, Spring disc coupling

13.2 Angle flangesThere are different versions. Their bore holes are designed for the differentflanges of the shaft encoders.

Figure 86, Angle flange, example

The angle flanges have a height of 80 mm to 100 mm, a width of 90 mm to110 mm and a depth of 40 mm.

13.3 Bearing blockThe bearing block provides a further mounting possibility for hollow shaftencoders. It can withstand high radial stress of the shaft.It is recommended especially for the use with measuring wheels, pulleys orchain wheels. It prevents overload of the encoder bearing.


Figure 87, Bearing block with angle flange

The bearing block has two different shafts. The smaller shaft with a flat onthe right in figure 87 has a diameter of 10 mm.The shaft on the left has adiameter of 12 mm.

High resistance The maximum permissible rotational speed is 6,000 min -1. The shaft can beloaded with 200 N axial and 200 N radial. Thus the shaft load is many timeshigher than for shaft encoders.A matching angle flange is offered as a further accessory.

13.4 Isolating adapterThe isolating adapter is for shaft encoders with synchro flange. It consists ofplastic (PBTP) and provides mechanical as well as isolation protection.

Figure 88, Isolating adapter

The cap has a diameter of 63 mm. The diameter of the flange is 82 mm.The depth is 38 mm.

13.5 Pinion and rackA pinion on the shaft of the encoder in connection with a rack enablesdirect transmission of linear movements.

Figure 89, Pinion


The pinion has 20 teeth and a circumference of 50 mm. It is designed for anaxle diameter of 6 mm. A pinion with a bore hole of 10 mm is also available.

Figure 90, Rack

The rack is 5 mm thick and it is available in lengths of 500 mm and 1,000mm. Fixing holes have to be drilled by the user.If possible the rack should be mounted with the teeth downwards. Thusmalfunctions due to dust or chips can be avoided. Measuring wheels andpinions are usually mounted directly on the encoder shaft without a flexiblecoupling.

13.6 Resilient baseIn order to protect shaft encoders against mechanical overload due to theuse of pinions and racks the units can be mounted on a resilient base.

A B

C

Figure 91, Resilient base

13.7 Measuring wheelMeasuring wheels are available with circumferences of 200 mm and 500mm. The measuring wheel with a circumference of 200 mm is available forshaft diameters of 6 or 10 mm, the measuring wheel with a circumferenceof 500 mm only for a shaft diameter of 10 mm.


Figure 92, Measuring wheel

Measuring wheels are either completely made of aluminium, the tread isknurled axially (strongly roughened); or they are made of plastics withdifferent surfaces. These can be: rubber, smooth plastic or grooved plastic.

Non-slip For choosing the measuring wheel it is important that the wheel can moveon the surface without any slip.Examples:

Surface of the measuring distance: Coating of the measuring wheel:,Glass RubberMetal RubberWood possibly aluminiumrubber aluminium

Figure 93, Measuring wheels, rubber, plastic, smooth aluminium,roughened aluminium

A disadvantage of rubber is the wear due to abrasion and that thetemperature resistance is not very high.


A

B

C

Figure 94, Measuring wheel on moving arm

If a measuring wheel is used it may also be recommendable to place theshaft encoder on a resilient base.

13.8 Fastening clampThese small discs are for fastening shaft encoders with synchro flange.

Figure 95, Fastening clamp

The diameter is only 12 mm. They are 5.5 mm thick. The bore hole has adiameter of 4.2 mm. The lip is 3 mm thick.

13.9 Pulse divider, pulse stretcherWith pulse dividers and pulse stretchers high frequencies or short pulses canbe adapted to low input frequencies of evaluation systems and controllers.They modify high signal frequencies or short pulses in such a way that theycan be detected by standard inputs of plcs or electronic counters. The use ofa pulse divider thus eliminates the need of fast input cards of a plc.Furthermore the pulse divider can be used as level converter of TTL or HTLsignals.

13.9.1 Pulse divider

The pulse sequence of incremental shaft encoders can be very fast,depending of the resolution and rotational speed. The input frequency ofthe standard inputs of a plc or an electronic counter is maybe not highenough to detect all pulses of the shaft encoder.By using a pulse divider the high frequency of the signal outputs of the shaftencoder can be divided so that it can be detected by the plc. Thedisadvantage is that the accuracy is reduced.


E 80102plc

shaft encoder

Figure 96, Pulse divider E80102, connection

Depending on the version of the pulse divider the division ratio of the inputto the output can be freely selected between 1 and 255 (E80102) or it isfixed to 10:1 (E80100).

13.9.2 Pulse stretcher

The pulse stretcher converts short input pulses into output pulses with aconstant length.

Figure 97, Pulse stretcher E80110

The input pulse (IN) length of the pulse stretcher must be at least 0.2 ms.The pulse length on the output (OUT) is 25 ms. There must be at least 28ms between the input pulses.


14 Mounting of shaft encodersThe mounting of shaft encoders is especially important. Misalignmentbetween drive and encoder shaft can considerably impair the operation ofthe shaft encoder.

AB

C D

Figure 98, Figure 98: Mounting with coupling

The shaft encoder can be mounted by means of:

Mounting holes on the front face of the shaft encoder.Fastening clampsClamping.

Figure 99, Mounting with fastening clamp

Not the cap Solid shaft encoders must never be fixed outside the flange. The housingcap is made of aluminium and can be deformed relatively easily. It providesno secure hold.Hollow shaft encoders are mounted directly on the driving part, the hollowshaft being connected to the driving shaft.


Figure 100, Hollow shaft encoder with shaft open on one side

3. SW 3

4x M4

Figure 101, Hollow shaft encoder with continuous hollow shaft


15 Calculation examples

15.1 Linear measurementTo calculate the resolution, the circumference of the pinion or themeasuring wheel and the requested resolution have to be known.Example:A pinion with a circumference of 50 mm is used, the required resolution is0.1 mm.With each 0.1 mm-step a pulse is to be generated, this results in a total of500 pulses for one complete revolution. The shaft encoder in this exampleneeds to have a resolution of 500 increments.For the resolution in millimetres the following applies: Number ofincrements = circumference (in millimetres).

15.2 Switching frequency and mechanicalrotational speed

Correlations between maximum mechanical rotational speed, switchingfrequency and resolution:Note: With a high resolution the electrical switching frequency is quicklyexceeded.The indication of the maximum mechanical rotational speed only refers tothe mechanical load of the shaft encoder.Example: Encoder RU1045, type RU-5000-I05/L2Max. mechanical rotational speed: 12,000 min -1 = 200 s-1

Maximum switching frequency (electr.): 300 kHzA maximum resolution of 5,000 pulses and maximum mechanical rotationalspeed result in a switching frequency of:200 s1 X 5,000 = 1,000,000 Hz = 1 MHz.Thus the maximum possible switching frequency of this shaft encoder isexceeded by more than three times.


16 Handling of shaft encodersBetter not ...

Figure 102, No overvoltage, do not align with a hammer

Figure 103, Do not clamp into the vice, do not drill into the shaft

Figure 104, Do not saw or grind the shaft


17 ApplicationsShaft encoders are used in the following industries for example:

Metallurgical, milling and steelworks equipmentPlant and apparatus construction in general (e.g.hydraulics,pneumatics, welding systems, presses, stamping machines, drillingmachines)Machine toolsTransfer linesSpecial machinesSurface treatment machinesProcessing machines for wood, paper, plasticsPrinting and labelling machinesMounting systemsBig antenna systemsIndustrial robotsConveyor and transport systemsConstruction of lifts, escalatorsRoller shutter doorsStacking systemsCranes and lifting systems

Figure 105, Measuring wheel for linear measurement

Incremental shaft encoders in connection with a counter enable automaticcutting of e.g. sheets of veneer to a specified length.


Figure 106, High-lift shelves

In this case multiturn shaft encoders are used to enable exact positioning ofthe transport system and automatic loading and unloading.To ensure safe data transmission via longer distances multiturn shaftencoders with SSI interface are used.


Figure 107, Robots

Absolute shaft encoders are used for the precise control of the movementof industrial robots and automatic handling systems. They guarantee furtherprocessing e.g. after a power failure without any problems, thus makingcomplex returning to a reference point superfluous.

Figure 108, X-Y-Z-milling system

The individual positions and travel lengths of an automatic machiningsystem are detected by incremental encoders with up to 10,000 pulses perrevolution. This allows resolutions up to 0.01 mm.


18 Annex

18.1 CompetitorsThere are many competitors on the market for shaft encoders with anoptical principle. Heidenhain, Hengstler, Stegmann, Balluff, IVO, TWK, T2R,Litton and Baumer are some of the most important ones.

18.2 Glossary of technical termsStarting torque The starting torque of a shaft encoder is the torque required to cause the

shaft to change from the off position to a rotational movement.Absolute shaft encoder Encoder which provides clear, coded information for each measuring step.Scanning frequency The number of signal periods per second. The maximum scanning frequency

limits the speed of incremental systems.Alarm signal It serves to monitor the shaft encoder as regards malfunctions, e.g. disc

breakage, soiling, short circuit of the signal wire, and insufficient supplyvoltage.

Analogue signal A signal which continuously changes its level.Complementary Output stage where the inverted signals are provided as well. Electrically the

I/O levels are transmitted in the form of voltage differences between twowires. Thus the useful signal (the difference) remains uncorrupted, asinterference usually occurs on both wires.

ASCII The name ASCII stands for ´American Standard Code for InformationInterchange´. It is a code standardised in the USA to represent alphanumericcharacters. Originally based on a 7-bit coding it enabled the representationof 128 characters. Extended to 8 bits it became the standard code on smallcomputers. Due to this extension 128 characters became possible which arenowadays partly used as checksum or to represent country-specificcharacters.The ASCII code is currently the standard code to store unformatted textfiles.

ASIC User-specific IC.Resolution Number of measuring steps (gratings) within a measuring range.Axial load Maximum load of the encoder shaft in axial direction � looking at the front

face of the shaft in the direction of the flange.Baud rate Speed of the data transmission (bits per second).BCD Binary-coded-decimal; binary representation of a decimal number (one

decade).Bimetal A bimetal strip consists of two different metals which have a different

expansion at different temperatures. Both metal strips are bonded together.These bimetal strips can also be used to manufacture temperature meters.

Binary Two logic states (yes/no, ON/OFF, HIGH/LOW). Basis for dual computersystems.

Binary code The basis for each binary code is a so-called binary system, i.e. a system withonly two states, for example ON/OFF, true/false, 0 Volt/5 Volts or the binarycode 1/0.The binary code is a code which only works with two characters: the binaryzero and the binary one. The basic unit is the bit, a storage place which canonly take the values 0 or 1. Eight such bits combined are called byte. Thusone byte can represent 256 characters.

Bit Abbreviation for "binary digit"; smallest information unit of a binary systemthe value of which can be I or 0 (yes/no decision).

Byte Sequence of 8 bits. One byte has 8 bits.


Data transmission, parallel Each individual track has one data wire. The data are either constantlyavailable or they are provided via an enable signal. Example: With aresolution of 4096 steps (12 bits) there are 12 wires.

Dual The expression "dual" refers to the representation of numbers.Code Format of the data transmission.Data valid Output for checking the validity of data.Data bus System of wires for parallel or serial electronic data transmission.Data transmission, synchronous-serial With transmission in this format all data are transmitted in succession on

one data wire. Only 4 cable cores are required: Clock, clock negated, dataand data negated. In the case of shaft encoders with synchronous-serialinterface, the inverted data are provided as well to increase the noiseimmunity. Depending on the clock frequency cable lengths of up to 100 mare possible.

DC Direct voltageDIN Deutsche Industrie-Norm (German industrial standard).Revolution, maximum mechanical Maximum permissible revolution of the encoder shaft. The maximum value

is stated in the data sheet together with the other mechanical data.Dual code Natural binary code, code often used with absolute shaft encoders.EBCDIC This abbreviation stands for 'Extended Binary Coded Decimal Interchange

Code'. It is used on mainframes to represent characters. This code wasintroduced by IBM in 1965 and has not changed up to now.

EEPROM Also E2-PROM. Abbreviation for "Electrically Erasable Programmable Read-Only Memory".

EMC Electromagnetic compatibility.Enable Control input via which the data outputs can be enabled.EPROM "Erasable Programmable Read-Only Memory"; read-only memory which is

erasable with UV light and can therefore be rewritten.Flange socket Connector which is mounted directly on the encoder housing.Encoder monitoring see alarm signalEncoder supply The supply voltage to be supplied to the shaft encoder.Encoder accuracy Deviation between the actual position and the measured position.Gray-Code The Gray code is a different way of representing the binary code. The basis

is that two adjacent bit combinations must not differ in more than one bit(0 or 1). This is an advantage especially if as many data as possible are to bestored. A further benefit is the possibility to detect errors in the transmissionof such codes more easily because adjacent characters may only differ inone position (valid for Ub of 24 V DC and maximum current rating).

HTL output Abbreviation for ´High Threshold Level´. The output level is more than 21Volts. The counterpart is the TTL output.

Interpolation electronics It converts a sinusoida l period into several square-wave pulse trains bymeans of an additional division, thus achieving a considerably highermeasuring resolution.

LSB Least Significant BitMbaud Megabits per second. Information about a data transmission speed.MSB Most Significant BitMultiturn shaft encoder The multiturn shaft encoder does not only count the resolution of a

revolution but also the number of revolutions.Parity bit (even) A parity bit (check bit) is added to the transmitted data in order to achieve

an even number of bits.PC Personal computer.PUR Standard cable material (polyurethane) for all shaft encoders with more than

three output signals. According to VDE 0672 the PUR cables are resistant tooil as well as hydrolysis and microbes.


PVC Standard material for the sheathing. In order to avoid cable break PVCcables must not be moved if the temperature falls below -5 °C.

Radial load Maximum load of the encoder shaft in radial direction (parallel to the flangeat the outer end of the shaft).

RS422/485 Interfaces for serial data transmission with values according to the EIAstandard.

RS422 Standardised interface for unidirectional point-to-point connection.RS485 Like RS422, but as bidirectional bus interface.Interface Interface point with defined connections, signals and signal sequences.Protection rating IP 50 Complete protection against contact with live parts or internal moving parts.

Protection against harmful dust deposits. The ingress of dust is notcompletely prevented but dust must not penetrate in such quantity as toimpair the operation. No special protection against ingress of water.

Protection rating IP 64 Complete protection against contact with live parts or internal moving parts.Protection against the ingress of dust and splashing water. Water splashedonto the equipment from any direction shall have no harmful effect.

Protecting rating IP 65 Complete protection against contact with live parts or internal moving parts.Protection against the ingress of dust and water jets. A water jet from anozzle, aimed at the equipment from any direction shall have no harmfuleffect.

Protecting rating IP 66 Complete protection against contact with live parts or internal moving parts.Protection against the ingress of dust and powerful water jets. Water mustnot penetrate the equipment in harmful quantities in case of temporarypowerful water jets.

Singleturn encoder The singleturn encoder resolves a mechanical revolution of the shaft into anumber of code values corresponding to the resolution. A code value isassigned to each angular position within a revolution.

Shock resistance Maximum permissible short-time value of a shock load.Interference signal For 10 to 30 V shaft encoders with axial or radial flange connectors this

signal is on PIN 7. It can be used for monitoring the encoder. In case of aproblem the signal changes from HIGH to LOW level.

Synchronous-serial right-justified format Like with the triangular format (see below) the shaft encoder alwaysprovides data bits via 25 clock pulses also in this case. In case of a scaling,however, the 'zeros' are always put before the complete positioninformation.

Triangular format (SSI) For SSI transmission of the position values a differentiation is made betweenmultiturn (12 bits) and singleturn (13 bits). Therefore data bits are alwaysread over 25 clock pulses, but the data content may vary. The resolution ofthe multiturn reduced by means of a scaling is filled with preceding 'zeros'.In case of a reduced singleturn resolution the 'zeros' are added at the end.

TTL output "Transistor-transistor-logic" on a 5-Volt basis. The counterpart is the HTLoutput.

Operating temperature Temperature range at which all electrical and mechanical data are met.Vibration The value of a periodical oscillation at which the unit does not show any

malfunction or is not destroyed when in permanent operation. It is stated ing for the frequency range 58 � 2000 Hz.

Virtual zero point The SSI controller enables the user to set a zero point independently of theshaft encoder.

Shaft load The shaft load is the maximum permissible load on the shaft, referred to theshaft end at maximum mechanical revolution and 20°C operatingtemperature.


Angular second Angle sizes are stated in degrees. One angular second is the 3,600 th part ofa degree. A full circle with 360 degrees therefore has 1,296,000 angularseconds.


19 Type key

May 2004


19.1 Examples of the use of the type keyA type key is often also described as 'talking type key' because the mostimportant technical data can be read from the type designation by means ofthe type key.Once fixed, the type key may reach its limits with an increasing variety ofunit types. In that case a completely new type key must be created. ingeneral it is useful only to work with the article number. All organisationalprocesses at ifm electronic use the article number.

A shaft encoder with the article number RU6071 has the type designationRU-0100-I24/L2E.If the type key is known this type designation provides the followinginformation:

Position: 1 2 3 - 7 8 9 10 - 11 12 13 14 15R U - 0100 - I 24 / L 2 E

Position 1: shaft encoderPosition 2: solid shaft encoder 58 mm with synchro flange

standard 6 mm shaftPositions 3 � 7: 100 incrementsPosition 8: reservePosition 9: incremental output signalsPositions 10 -11: 10 � 30 V DCPosition 12: reservePosition 13: cable entry axialPosition 14: 2 m cable lengthPosition 15: protection rating IP66

Another shaft encoder with the article number RM 1102 has the typedesignation RM-8192-E05/R5B.

Position: 1 2 3 - 7 8 9 10 - 11 12 13 14 15R M - 8192 - E 05 / R 5 B

Position 1: shaft encoderPosition 2: multiturn shaft encoder 58 mmPositions 3 -7: max. 8192 (25 bits) steps per revolution, 4096

revolutionsPosition 8: reservePosition 9: Profibus interface, connection to gatewayPositions 10 -11: 5 V DC (TTL, from the gateway)Position 12: reservePosition 13: cable entry radial with cable plug ifm 1001.1Position 14: 5 m cable lengthPosition 15: 10 mm shaft


20 List of figuresFigure 1, Linear measurement and synchronous movement moni toring....................................................................7Figure 2, Detection of rotational speed and angle measurement...............................................................................7Figure 3, Bending systems and X-Y-recorders drawing tables ....................................................................................8Figure 4, Level measurement and radar/aerial systems ..............................................................................................8Figure 5, Industrial robots .........................................................................................................................................8Figure 6, Potentiometer ..........................................................................................................................................11Figure 7, Resolver....................................................................................................................................................11Figure 8, Inductive principle (Novotechnik) ..............................................................................................................12Figure 9, Magnetic principle....................................................................................................................................13Figure 10, Mechanical shaft encoder (cam-operated switchgroup)..........................................................................13Figure 11, Cam-operated switchgroup with inductive proximit y switches................................................................14Figure 12, Inductive system.....................................................................................................................................14Figure 13, Incremental shaft encoder ......................................................................................................................15Figure 14, Incremental shaft encoder ......................................................................................................................19Figure 15, Coded disc with increments ...................................................................................................................19Figure 16, Photoelectric detection, through-beam method .....................................................................................20Figure 17, Scanning plate, without reference mark grating.....................................................................................21Figure 18, Light source and condenser....................................................................................................................21Figure 19, Sine wave of the photo elements ...........................................................................................................22Figure 20, Connection of the photo elements.........................................................................................................22Figure 21, Signal voltage.........................................................................................................................................22Figure 22, Pulse generation.....................................................................................................................................23Figure 23, Signal generation, block diagram ...........................................................................................................24Figure 24, Pulse diagram channels A, B, and zero index (NI)....................................................................................25Figure 25, Zero index 360 degrees long (NI), type RB, 10 � 30 V .............................................................................26Figure 26, Pulse diagram with inverted channels (NI: Zero index) ............................................................................26Figure 27, Sinusoidal output signals (Vss = Vpp)......................................................................................................27Figure 28, Signal change.........................................................................................................................................28Figure 29, Duplication of the pulses ........................................................................................................................29Figure 30, Pulse multiplication.................................................................................................................................29Figure 31, Coded discs............................................................................................................................................31Figure 32, Photoelectric detection, through-beam method .....................................................................................32Figure 33, Pulse diagram of the parallel interface........ ............................................................................................33Figure 34, Gear box with coded discs and Hall elements .........................................................................................34Figure 35, Multiturn encoder, 4 bits singleturn, 3 bits mu ltiturn..............................................................................35Figure 36, Dual code...............................................................................................................................................36Figure 37, Gray code...............................................................................................................................................36Figure 38, Gray excess code ....................................................................................................................................37Figure 39, Cut Gray code for the value 360 ............................................................................................................38Figure 40, Code types .............................................................................................................................................39Figure 41, SSI interface unit RM ..............................................................................................................................40Figure 42, SSI, pulse diagram for singleturn shaft encoders.....................................................................................41Figure 43, SSI, pulse diagram for multiturn shaft encoders ......................................................................................41Figure 44, SSI interface, incremental signal shape ...................................................................................................42Figure 45, SSI interface, block diagram ...................................................................................................................42Figure 46, SSI programming software .....................................................................................................................43Figure 47, SSI programming software, connection ............. .....................................................................................44Figure 48, SSI interface, circuit example ..................................................................................................................44Figure 49, SSI controller ..........................................................................................................................................45Figure 50, SSI controller, connections......................................................................................................................45Figure 51, Profibus DP shaft encoder, type RM .......................................................................................................46


Figure 52, Profibus DP.............................................................................................................................................47Figure 53, Profibus, addressing and terminating resistor ..........................................................................................47Figure 54, Mark-to-space ratio ................................................................................................................................49Figure 55, Phase difference .....................................................................................................................................49Figure 56, Solid shaft encoder .................................................................................................................................51Figure 57, Ball bearing (K) with sealing ring (D) .......................................................................................................52Figure 58, Flange with threaded holes (G) ...............................................................................................................53Figure 59, Flange types (1, 2, 3 � see above) ...........................................................................................................53Figure 60, Clamp, synchro and round flange...........................................................................................................53Figure 61, Hollow shaft encoders ............................................................................................................................54Figure 62, Hollow shaft encoder, cut-away view ..... ................................................................................................55Figure 63, Stator coupling for hollow shaft encoder................................................................................................55Figure 64, Cable entry axial (A) and radial (R) ..........................................................................................................56Figure 65, Cable entry for small units ......................................................................................................................57Figure 66, Cable plug..............................................................................................................................................57Figure 67, Connector unit .......................................................................................................................................58Figure 68, Pin connection of a plug.........................................................................................................................58Figure 69, Coupling, electrical .................................................................................................................................58Figure 70, Earthing and screening ...........................................................................................................................59Figure 71, Rotational speed and switching frequency.......... ....................................................................................61Figure 72, Shaft load, axial (A) and radial (R) ...........................................................................................................61Figure 73, Transient condition of the TTL voltage ....................................................................................................64Figure 74, Residual ripple of the signal outputs ....... ................................................................................................64Figure 75, Encoder supply with external power supply ..... .......................................................................................65Figure 76, Resolution and rotational speed..............................................................................................................68Figure 77, Cable length and output frequency, TTL.................................................................................................68Figure 78, Cable length and output frequency, HTL ................ ................................................................................69Figure 79, Operating instructions, example .............................................................................................................71Figure 80, Data sheet of the shaft encoder RV1009 ................................................................................................72Figure 81, Data sheet of the shaft encoder RM6001 ...............................................................................................73Figure 82, Flexible coupling .....................................................................................................................................74Figure 83, Axial, radial and angular displacement....................................................................................................75Figure 84, Flexible coupling with different bore holes ..............................................................................................76Figure 85, Spring disc coupling................................................................................................................................76Figure 86, Angle flange, example ............................................................................................................................76Figure 87, Bearing block with angle flange..............................................................................................................77Figure 88, Isolating adapter.....................................................................................................................................77Figure 89, Pinion .....................................................................................................................................................77Figure 90, Rack .......................................................................................................................................................78Figure 91, Resilient base ..........................................................................................................................................78Figure 92, Measuring wheel ....................................................................................................................................79Figure 93, Measuring wheels, rubber, plastic, smooth aluminium, roughened aluminium .......................................79Figure 94, Measuring wheel on moving arm ...........................................................................................................80Figure 95, Fastening clamp......................................................................................................................................80Figure 96, Pulse divider E80102, connection ...........................................................................................................81Figure 97, Pulse stretcher E80110 ...........................................................................................................................81Figure 98, Figure 98: Mounting with coupling.........................................................................................................82Figure 99, Mounting with fastening clamp..............................................................................................................82Figure 100, Hollow shaft encoder with shaft open on one side ...............................................................................83Figure 101, Hollow shaft encoder with continuous hollow shaf t .............................................................................83Figure 102, No overvoltage, do not align with a hammer........................................................................................85Figure 103, Do not clamp into the vice, do not drill into the shaft ...........................................................................85Figure 104, Do not saw or grind the shaft...............................................................................................................85


Figure 105, Measuring wheel for linear measurement............ .................................................................................86Figure 106, High-lift shelves ....................................................................................................................................87Figure 107, Robots..................................................................................................................................................88Figure 108, X-Y-Z-milling system.............................................................................................................................88


21 Index

990-degree-shift 22

AAbsolute shaft encoders 29Acceleration 60Accessories 70Accuracy of the shaft encoder 47Angle flanges 72angular displacement 71Applikationen 82axial displacement 71

BBall bearing 49BCD code 35Bearing block 72Binär-Code 34

CCalculation examples 80Capacitive principle 13Clamp flange 51Code types 34Coded disc 18Condenser 20Connection 32Connection cable 54Connector 55counting 33Couplings 70Current consumption 63Current rating 63

DData sheet 68Data transmission 39DC component 21Decadic Gray excess-3-code 37Detection of the direction 27DIADUR 18DIADUR method 15Direction of rotation 33Dividing error 47Dual-Code 34

EEarthing 57Electrical connection 54Electrical data 61Enable signal 32external evaluation electronics 62

FFAQ 10Fastening clamp 76Flange types 50

GGrating period 20Gray code 35Gray excess code 36Grub screw 71

HHall-effect sensors 33Handling 81Hollow shaft encoders 51Housing material 60hro flange 51HTL voltage range 61

IIncremental shaft encoders 17Increments 18Inductive principle 12Inductive system 14input frequency 59Interference signal 27Inverted output signals 25Isolating adapter 73

LLaying the cable 56LED 63Light-emitting diodes 63Limit frequency 58Linear measurement 80Linear movement 7LSB 32


MMagnetic principle 12mark-to-space 23Mark-to-space ratio 48Measuring step 24Measuring wheel 74Mechanical data 58Mechanical rotational speed 58Mechanical shaft encoders 13Mounting 53Mounting of shaft encoders 78MSB 32Multiplex operation 33Multiturn shaft encoders 33

OOperating instructions 67Operating temperature 60Oscillator sensors 14

PPhase difference 48Phase discriminator 27Photo elements 21Photoelectric shaft encoders 14photoresist 15Potentiometers 11Profibus-DP interface 45Protection rating 60Pulse diagram 23Pulse divider 76Pulse multiplication 28pulse stretcher 76

Rrack 73radial displacement 71Reference mark 20Reference mark outside 25Reflectible Gray code 35Residual ripple 61Resilient base 74Resolution 19, 31Resolvers 11Rotational movement 7

Round flange 51

SScanning plate 20screening 57Sensor cables 62Shaft encoders 17Shaft load 59Shock resistance 60Signal evaluation 22Signal frequency 64Signal generation 19Signal generation of the photo elements 20Singleturn shaft encoders 31Sinusoidal signals 26Sockets/coupling 56Solid shaft encoders 49Square-wave pulse trains 22SSI controller 43SSI interface 39Standard resolutions 19Starting torque 50stator coupling 52Storage temperature 60system accuracy 15

Ttechnical terms 85Through-beam method 19transducer 9TTL voltage range 61Type key 88

VVibration 60vibration resistance 60Voltage supply 61

WWiring 26

Zzero index 20


22 SourceSome diagrams and figures were taken from literature/catalogues of thecompany Heidenhain.

T H E E N D

Documents

ifm electronic gmbh Sensors, networking and control ... · section instead of a keyword. To differentiate them from simple keywords, they are written in italics. 2.1 On the contents