iemece.files.wordpress.com · Web viewINSTITUTE OF ENGINEERING AND MANAGEMENT. DEPARTMENT OF ELECTRONICS AND COMMUNICATION. ENGINEERING. ELECTRONIC MEASUREMENT & INSTRUMENTATION

INSTITUTE OF ENGINEERING AND MANAGEMENT

DEPARTMENT OF ELECTRONICS AND COMMUNICATIONENGINEERING

ELECTRONIC MEASUREMENT & INSTRUMENTATION LABORATORY: EC-395C

DEPARTMENT VISION

Provide Quality Education in Electronics, Communication and Allied Engineering fields to serve as Valuable Resource for Industry and Society.

DEPARTMENT MISSION

1. Impart Sound Theoretical Concepts and Practical Skills.2. Promote Inter-disciplinary Research.3. Inculcate Professional Ethics.

Laboratory in-charges

1.Murari Shaw2.Mohidur Rehman

Lab course coordinators

Asst. Prof. Gautam Ghosh

COURSE OUTCOMES

Students will be able to:1. Understand how to correctly handle different types of Instruments and devices.2. What are the Precision and accuracy of Instruments and how they can calibrate these devices and Instruments? 3. What are the behavior of these Devices and Instruments at both A.C. and D.C. Currents?

PROGRAMME EDUCATION OBJECTIVESGraduates will be able to:-1. Work as professionals in the area of Electronics and Allied Engineering fields.2. Pursue higher studies and involve in interdisciplinary research work.3. Exhibit ethics, professional skills and leadership qualities in their profession.

EXPERIMENT-1

STATIC CHARACTERISTICS

Introduction :

Provision for Connection of Standard Meter Testing Meter terminalsPower supply terminals

There are two meters ------- one is Standard Meter and other is a Testing meter .

The Standard meter has full scale is 8 V and smallest division is 0.1 V The Testing meter has a Grafix Scale and its full scale division is 0.02 V. This Testing Meter is connected to Three variable resistances : 1 ----- Swamp Resistance , 2 ---- Shunt Resistances and 3 ---- Multiplier Resistances --------- these three resistances can be used for adjustment of meter calibration .

A precision grade power supply also helps for measurement of static Characteristics.

Standard Testing

12

3

+ _ + _

Grafix Scale

Objectives :

The experimental techniques for measurement of Accuracy , Precision , Repeatability , Hysteresis and Linearity of a Voltmeter.

Accuracy :It refers to how closely the measured value agrees with the true value . It is the maximum amount by which the measured value differs from the true value . Inaccuracy depends on systematic errors involved in the measurement.

The inaccuracy of an instrument can be specified as given below :

Measured value True value(i) Percentage of true value =

True value

Measured value True value

(ii) Percentage of full scale deflection ( f.s.d) = Maximum scale value

Experimental Procedure :

(i) Set the supply voltage at 2 V and adjust Testing meter using Shunt / Swamp / Multiplier resistance.

(ii) Set the supply voltage in between 2 V and 2.1 V using Standard meter.(iii) Observe the reading at Standard meter ( say, 2.06 V ) .(iv) Repeat for other three sets of readings.

Table I

No. of obs. Standard Meter Testing Meter

1. Between 2.0 V and 2.1 V 2.06 V

2. between 3.0 V and 3.1 V 3.04 V

3. Between 3.9V and 4.0 V 3.92 V

4. Between 4.5 V and 4.6V 4.54 V

Calculation :

2 – 2.06 Percentage of the True value = x 100 % 2.06

= 2.9 %

2 – 2.06 Percentage of full scale deflection ( f,s,d) = x 100%8 V

= 0.75 %

Precision :

Precision of measurement of a variable is the ability of obtaining nearly the same value when the same measurement is repeated . In other words , it indicates the ability to reproduce a measured value within a given limit , every time the same measurement is carried out . It is the agreement of various readings among themselves . If output is constant , several repeat readings of the output O1 , O2 , O3 ------ On etc . , are close to one another within a small difference . The smaller the difference the more precise is the measurement . Precision leads to repeatability , that the ability of the measurement system to give the output for the same input repeatability .

Largest deviation - Average Repeatability = x 100 % Full scale

Where the largest deviation is the reading farthest from the average , either above or below .


1. Set the supply voltage at 2 V using Standard meter and adjust the Testing meter voltage using Swamp / Shunt / Multiplier resistance.

2. Set the supply voltage at 5 V using Standard meter.3. Measure the voltage at Testing Meter.4. Put off the power supply and again switch ON ; Measure the Standard and Testing

meter.5. Repeat the above procedures in ten times and record your observations.

Table II

Input voltage Vin = 5 V

No. of obs. Standard Meter Testing Meter

1

2

3

4

5

6

7

8

9

10

For instance it is required to measure 5 V . Six measurements are taken the six values are 5.02 V , 5.02 V , 5.0 V , 4.98 V 5.0 V, 5.02 V – for a true voltage of 5 the largest measured value is 5.02 V . The measurement could be in the error by 2 % . But the variation of the five readings is + - 0.006 % because the maximum deviation from the mean value of 5.006 is only 0.006 Volt. Thus the precision of measurement is +-0.6 %.

Hysteresis :

Hysteresis is the difference in the output for a given input when the input is increasing and output for the same input when the same input is decreasing , i.e.,

Hysteresis = O I - OI

It is the inability of an instrument to repeat its reading while going up – scale compared with the reading while going down scale , or the inability of the device to maintain its operating point with increasing or decreasing inputs. It is an error that could be due to friction , backlash , incomplete recovery from stress , magnetic or thermal effects etc.

OutputOmax P

b

Hm

a

OminO Input

Fig.1. Hysteresis curve.

If the input follows a curve OaP when output is increasing , it may follow a curve PbO when input is decreasing. The difference ab is the Hysteresis H

Maximum value of hysteresis Hm can be taken from this curve . Hysteresis is usually expressed in terms of maximum hysteresis Hm as a percentage of span.

HmH =

Omax – O min


1. Set the supply voltage at 5 V using Standard meter and adjust the Testing meter voltage using Swamp / Shunt / Multiplier resistance.

2. Set the supply voltage at 0 V using Standard meter.3. Measure the voltage at Testing Meter.4. Slowly increase the voltage , ( say 0.5 V ) and measure this voltage using Testing

meter .5. Repeat this process till the voltage reaches 5 V.6. Now slowly decrease the input voltage in same way until zero voltage and record

your observation using Testing meter.7. Draw the input voltage Vs. output voltage . 8. Measure Hysteresis of the Testing meter.

Table II

No. of obs. Input Output

Standard Meter Testing Meter

1

2

3

4

5

6

7

8

9

10

Linearity :

The word ‘ Linearity’ is used to indicate ‘ Non- linearity’ . Non – Linearity is specified only for linear instruments. The non – linearity of an instrument indicates the maximum possible deviation of any reading from the theoretical linear characteristics of the instrument . To find out the non – linearity a set of known input values are given to the instrument and corresponding output readings are noted . from these readings maximum deviation , i.e. , the maximum difference between the indicated output reading and the corresponding input value , is identified and it is normally expressed as a percentage of the FSR ( Full Scale Reading ) .

Linearity may be specified several different ways . Three of the more popular techniques are end – point linearity , independent straight line linearity and least squares ( also called best fit or linear regression ) linearity.

For end – point linearity , a straight line is drawn between the two end – points of the calibration curve. If the theoretical value is zero and full scale input and output are used, the resulting number is called the theoretical shape linearity. You then determine the maximum deviation both above and below that straight line . These are reported as + -------- % and ------- % of full scale output .

Output

InputFig.2. End point Linearity

To determine independent straight line linearity , you draw two parallel straight lines which just which just enclose the calibration curve . The independent straight is drawn halfway between these two boundaries. You then determine and report the maximum deviation from the single , centered straight line as + -------- % , --------- % of full scale output.

Output

Input

Fig.3. Independent straight line Linearity

Least square linearity is measured from a statistically derived straight line . This is the straight line which the sum of the squared distance ( error ) is least or at a minimum ‘ . Given a set of x , y pairs , which is the calibration data ( input value on the X axis , output on the Y ) you can calculate the equation of the straight line that yields minimum error .

x = input values

y = Output values

m = slope of the straight line

b = y intercept of the straight line.

N = number of data points

n (x y ) – x y Σ Σ Σm = n (Σ x2 ) – ( Σ x ) 2

Σ y Σxb = - mn n

To calculation of the slope and the intercept of this best fit ( least squares) straight line can get a bit tedious .

Best fit least square straight line

Output

InputFig.4. Least square Linearity

EXPERIMENT-2

DYNAMIC CHARACTERISTICS

Introduction :

The quantity to be measured by an instrument could be either slowly or rapidly varying with time . when an instrument is used to measure quantities , which are either constant or vary very slowly with time , the quantities are termed as static characteristics .Dynamic quantities are those which vary with time and can be mainly with two types : Steady state periodic and Transient . An input whose magnitude has a definite repeating time cycle , is called steady state periodic , whereas an input , whose magnitude does not repeat with time , is termed as transient .

Dynamic performance characteristics

Two important aspects of dynamic response characteristics are :(a) Fidelity(b) Speed of response

Fidelity : Fidelity is the ability of the system to reproduce the output in the same form as input or it is system’s ability to present faithfully the information in the measured.

Fidelity is defined in terms of :(i) Amplitude response (ii) Frequency response

(i) Amplitude response:It is the ability of the system to treat all input amplitudes equally and uniformly . practically it may not be possible . So it is desired that over a specified range of input amplitudes the ratio of output amplitude to input amplitude should remain constant.

Gain

InputFig.1 . Input vs . Gain of a system.

(ii) Frequency Response :

It is the ability of the system to treat inputs , of all frequencies equally and uniformly . Again , practically it is desired that the ratio of output to input amplitudes should remain constant over same desired frequency range.

Gain

Frequency

Fig.2. Frequency vs. Gain of a system

Speed of Response :

The most important factor in the performance of a measuring system is that full effect of an input signal ( i.e. Change in measured quantity ) is not immediately shown at the output but is almost inevitably subject to some lag or delay in response . This is delay between cause and effect due to the natural inertia of the system and is known as measurement lag.

An important dynamic characteristics used in assessing the performance of measurement system is the response of the system when subject to a sudden change in the input signal ( Known as a step input ) . The resulting system response will depend on the type of system considered .

Speed of response is defined or judged by the following :

(i) Dead Time : It is time taken by the system to begin to respond after a change in the input.

(ii) Delay time or Rise time ( tr) : The time taken for the system output to rise from 10 % to 90 % of its final steady state value .

Vin

t

Vout

t

Fig.3. Response of a simple dead time element.

(iii) Response Time ( t res) :The time taken for the systeme output to rise 0 % to the first cross over point of 100 % of the Final steady state value . Applicable only to underdamped system.

(iv) Settling time ( t s) :The time taken for the system output to reach and remain within a certain percentage tolerance band of the final steady state value . Typical value would be 2 % and 5 % settling time.

Output

100%

90%

10%

tt r

t rest s

Fig.4 Step response illustrating response and settling time.

Dynamic performance:

All systems will to some extent fail to follow exactly a changing input and a measure of how well a system will respond is indicated by its dynamic specifications . These are expressed as step or transient parameters or frequency response parameters , depending on the type of input applied . Many systems , although different in nature , produce identical forms of response and this is due to the fact that the system dynamics are similar – i.e. the dynamic or differential equations are of the same form .

For this reason engineers find it convenient to classify systems in terms of the type of system differential equations they have. They are following :

(i) First order systems(ii) Second order systems (iii) Third or Higher order systems

A common type of engineering is one that is modeled by a second order differential equation . Such a system is known as a second order system.

Second order Electrical System:

Fig.6. A general differential equation giving the angle of deflection of theθ Galvanometer coil at a time instant t when an instantaneous current i is passing at this time must take into account the following factors :

d2 θ(i) K = the retarding couple due to moment of inertia K of the coil dt2

d θ(ii) a = the retarding couple due to damping which is assumed to be dt proportional to the angular velocity of the coil.

(iii) c = the restoring couple due to the suspension fiber .θ

(iv) nABi = Gi , the displacement couple due to current i.(v) An opposition to the motion of the coil due to the opposing Lenz’s law currents

in the coil itself as it moves in the magnetic field , if the galvanometer is in closed circuit. This opposing e.m.f. depends on the rate of cutting of flux by the coil . It is therefore equal to the coil angular velocity multiplied by the effective area of the coil times its number of terns , i.e. the Electromagnetic damping due to this emf = nAB d / dt = G d / dt θ θ

(vi) An opposing emf e = - L di / dt , where L is the inductance of the galvanometer and its circuit.

If .therefore , the galvanometer is in closed circuit of total resistance R where R is the sum of galvanometer resistance R1 , then when a constant emf E is applied to the circuit terminals , the current i at time t during the motion of the coil is given by

E - G d - L di E - G d θ θdt dt dt i = = R R

Where L is neglected , or the current i is constant ( i.e. di / dt = 0 ) .

Equating this deflecting torque to the restoring torque due to factors (i) , (ii) and (iii) , the differential equation is

d2 d G d θ θ θK + a + c = G I = ( E – G )θdt2 dt R dt

or , d2 d GE θ θK + b + c = θ -------------( i)dt2 dt R

Where b = ( a + G2 / R ) and the electromagnetic damping dependent on G2 / R is added to the damping determined by a .

When the galvanometer is used for the measurement of a steady current I or emf E . then GI and GE / R will be continuously applied couples . The resultant final deflection

D will be given by equation I = c D / nAB , but the motion of the coil in attaining theθ θ deflection , oscillatory or otherwise will depend on equation (i) . when the galvanometer is used ballistically for the charge measurement , then GI = 0 during the motion of the coil before it moved significantly .

The equation may be rewritten as

d2 d θ θ+ 2p + q2 = f -------------(i i)θdt2 dt

where p , q and f are constants .

The solution of this equation is

b2 c b- exp [ - bt / 2 K ] + )

= [ ( 4Kθ 2 K 2K

2 b2 c

4K2 K

b2 c exp [ t ] 4K2 K

b2 c b b2 c + ( ) exp [ - t ] D + Dθ θ4K2 K 2K 4K2 K

-------------------------------------------- (iii )

The motion being non – oscillatory since p2 > q2 , i.e b2 / 4 K2> c / K

i.e. b2> 4 K c . But b = ( a + G2 / R ) . therefore ( a + G2 / R ) > 4 Kc , for non – oscillatory , or aperiodic motion .

On the other hand , if p2 < q2 then p2 - q2 is imaginary ,

Equation (iii) represents a damped , simple harmonic motion of which the amplitudes dies away , leaving

= D.θ θ

The angular frequency of this oscillation is decided by w = p2 - q2 therefore

The frequency f is given by :

W p2 - q2f = = 2 2 Π Π

2 Πand the period T = c ( a + G2 /R )

K 4K2

Which is different from the undamped period of oscillation because of the term

( a + G2 /R )

4K2

The rate at which the amplitude of the oscillation dies away is governed by

exp [ - pt ] = exp { - ( a + G2 /R ) t / 2K }

Critical damping is obtained when the coil motion is just non oscillatory . Therefore the frequency of oscillation is fulfilled when :

c ( a + G2 /R )= K 4K2

The damping factor ‘a ‘ , due to air , friction and neighbouring masses of metal , can usually be neglected when the resistance R is responsible for significant damping . Consequently critical damping is achieved when

G4

c = 4K2R2

Since , c , K and G are design constants of the suspension and coil respectively ., and R = R1 + Rg where R1 is the external circuit resistance and rg the galvanometer resistance .

Fig.5. Damped oscillations.


I . Amplitude Response Characteristics:

1. Select O/D ( Over Damped ) mode and connect the circuit as shown in Fig. and set the switch SW2 position.

2. Set the sine wave frequency = 1 KHz of the function Generator.3. Set the input voltage 0 and measure the output voltage . 4. Slowly increase the voltage at 0.5 V pp ( measured in CRO) and measure the

output voltage at the meter5. Repeat these process in steps until the output fall significantly .6. Draw the input voltage vs. Gain.

+A.C D.C

_ SW1 SW2 A

+ _

B

To CRO

COM O/D C/D O/D

Fig..6.Experimental circuit for Amplitude response characteristics.

II. Frequency Response Characteristics :

1. Select O/D ( Over Damped ) mode and connect the circuit as shown in Fig.6. and set the switch SW2 position.

2. Set the sine wave voltage = 6 Volt peak to peak .3. Set the sine wave frequency at 100 Hz and measure the output voltage in

meter.4. Gradually increase frequency and measure output voltage in the meter . Note

that input voltage does not vary with frequency.5. Draw the input frequency vs . Gain.

mA V

Function Gen.

Dynamic Response Characteristics :

+A.C D.C_ SW1 SW2 A+ _

B

COM O/D C/D O/D

Fig.7. Experimental circuit for study of Dynamic response.

1. Connect the circuit as shown in Fig. ( in over damped mode ) .2. Set the power supply voltage at 4 V and then switch off ( or disconnect the jumper

A ) .3. Press push switch and then simultaneously switch on the power supply ( or connect

the jumper A ) and start the ‘ stop watch.’ 4. Slowly the pointer of the meter moves and reaches at 4 V . Measure the time interval

.5. Repeat this process ten times.6. Connect the jumper B at C/D ( Critically Damped ) position. 7. Repeat steps 2 to 5.8. Connect the jumper at U/D ( Under Damped ) position .9. Repeat steps 2 to 3.

mAV

Power Supply

10. Rapidly the pointer of the meter moves and cross 4 V and reaches a maximum value and it will oscillate . Measure the time interval between 0 to maximum voltage. Record your observation.

11. Disconnect jumper A and again connect it . Next measure the second time interval and so on.

12. Draw time interval vs. output voltage.

Table

No. of obs. Initial Voltage Final Voltage Time interval

+A.C D.C_ SW1 SW2

+ _

+_ CLOSE OPEN

COM O/D C/D O/D

mAV

V

+A.C D.C

_ A

+ _

B

To CRO

COM O/D C/D O/D

Fig..6.Experimental circuit for Amplitude response characteristics.

II. Frequency Response Characteristics :

6. Select O/D ( Over Damped ) mode and connect the circuit as shown in Fig.6 position.

7. Set the sine wave voltage = 6 Volt peak to peak .8. Set the sine wave frequency at 100 Hz and measure the output voltage in

meter.9. Gradually increase frequency and measure output voltage in the meter . Note

that input voltage does not vary with frequency.10. Draw the input frequency vs . Gain.

V

Function Gen.

Dynamic Response Characteristics :

+A.C D.C_ A+ _

B

COM O/D C/D O/D Fig.7. Experimental circuit for study of Dynamic response.

13. Connect the circuit as shown in Fig. ( in over damped mode ) .14. Set the power supply voltage at 4 V and then switch off ( or disconnect the jumper

A ) .15. Press push switch and then switch on the power supply ( or connect the jumper A )

and start the ‘ stop watch.’ 16. Slowly the pointer of the meter moves and reaches at 4 V . Measure the time interval 17. Repeat this process ten times.18. Connect the jumper B at C/D ( Critically Damped ) position. 19. Repeat steps 2 to 5.20. Connect the jumper at U/D ( Under Damped ) position .21. Repeat steps 2 to 3.

V

Power Supply

EXPERIMENT-3

Digital Multimeter

Analog meter require no power supply , they give a better visual indication of changes and suffer less from electric noise and isolation problems . these meters are simple and inexpensive.

Digital meters , on the other hand , offers high accuracy , have a high input impedance and are smaller in size . They gives an unambiguous reading at greater viewing distances. The output available is electrical ( for interfacing with external equipment ) , in addition to a visual readout.

All Digital meters employ some kind of analog to digital ( A/D ) converters ( often dual slope integrating type ) and have a visible readout display at the converter output .

The basic circuit is always a DC voltmeter . Current is converted to voltage by passing it through a precision low shunt resistance while alternating current is converted into dc by employing rectifiers and filters for resistance measurement , the meter includes a precision low current source that is applied across the unknown resistance ; again this gives a dc voltage which is digitized and readout as ohms .

Modern digital Multimeter modules are versatile units that can easily be used to accurately measure voltage, current, resistance, and a whole lot more.

Digital Multimeter basics

Modern digital Multimeter (DMM) modules are basically sensitive high-resolution d.c. voltmeters that can be used to replace moving-coil meters in virtually all precision ‘analogue’ measuring applications. They combine a special A-to-D converter chip and an LCD or LED readout unit and a few other components into a compact module that consumes less than l mA from a power supply and costs little more than a good-quality moving-coil meter. Usually, these modules provide a 3 ½ digit readout and have a basic full-scale

measurement sensitivity of ±199.9mV, with 100 uV (200 - count) resolution and typical calibrated precision of 0.1 per cent ± 1 digit, but can he made to read any desired current or voltage range by connecting suitable shunts or dividers to the input terminals. When connected to suitable external circuitry the modules can also be made to indicate a.c. voltage or current, resistance, capacitance, frequency, or any other parameter that can be converted onto a linear analogue voltage or resistance.Most of these modules are designed around a (3E/lntersil ICL7IO6, 7126, or 7136 A-to-D converter chip. Each of these low-power CMOS ICs houses a precision A-to-D converter and LED drive circuitry, etc., in a 40-pin package. The A-to-D converter uses the dual-slope integration technique, with its inherent advantages of high noise rejection, near-perfect conversion

linearity, and non-critical clock frequency. The IC accepts a true differential input voltage and provides digital conversion accurate to within + - 1 count over the entire ±2000 count readout range; an auto-zero function ensures a zero reading at OV input, and polarity indication is automatic. All of the ICL 7107 internal action is controlled via clock signals derived from a built-in oscillator, which is set to operate at about 48kHz via R1—C1. This frequency is divided by four and then used to control a three-phase (signal integrate, reference de-integrate, and auto-zero) conversion cycle which occupies 16000 oscillator cycles, thus giving the DMM about three reading updates per second.

Basic DMM configurationsFig.1.shows the standard way of using the DMM as a 0 to l99.9mV d.c. meter, using the

100 mV bandgap voltage (from ROL and RFL) as a precision reference, and decimal point D3activated via XDP so that the unit reads ‘100.0’ when 100.O mV as applied between IN HI and IN LO.

+V

Input

- V

Fig.1. Standard 199.9 mV full scale connection of a DVM.

Fig.2shows the DVM connected as a precision ohmmeter. Here, the R1—R2 divider generates roughly 270mV between the RFH and COM terminals, and this voltage is used to energize the R ref - R x potential divider. Identical currents flow through these two resistors, and the generated voltage of Rref is applied across the RFH and RFL reference terminals, and that of R x , is applied across the IN HI and IN LO input; the display reading thus equals 1000 X Rx / Rref; if R x has a decade value (l k, 10k. etc.) the display gives a direct readout of the R x value (this reading is independent of the actual value of the R2

energizing voltage.

XDP

D3

Ref Hi

ROL

RFL

InLo

Com

+V

R1R ref 2.7K

R x R2 270 Ohm

-V

Fig.2. Precision Resistance meter , using ratiometeric technique.

Practical DMM applications

D.C. volt and current meters

A DMM module is usually supplied ready-calibrated to give a full-scale reading of ± 199.9mV d.c. It can be made to give alternative full-scale d.c. voltage readings by connecting the input voltage to the module via a decade potential divider, as shown in Figure 3, or can be made to act as a d.c. current meter by wiring a suitable shunt resistor across the input terminals, as shown in Figure 4. Note in both diagrams that the appropriate decimal point of the display must be activated, as shown.

XDP

RFH D1

D2RFLD3In Hi

In Lo

Com

+V

R1

Vin

R2

- V

Fig.3. A DVM can read alternative DC voltage range by connecting the input via potential divider.

+V

I in R1

- V

Fig.4. A DV M can be made to read DC current by connecting a shunt resistor across the input.Ohmmeters

ROH XDPRFH D1D2D3In Hi

ROL

RFLInLo

Com


ROL

RFLInLo

Com

The easiest and best way to use a DMM as a resistance (ohm) meter is to use it in the ratiometric configuration of Fig.5.This technique has two major advantages. First, it is very stable and inherently self-calibrating, the meter reading being equal to Rx X (rat / R ref ), where ‘rat’ is the DVM’s ratiometric value when used in the Fig.5test circuit: ‘rat’ is typically only 0.1 per cent low (0.1 per cent below unity), so measurement accuracy is determined primarily by R ref . The second advantage is that very low test voltages are generated across R x , at maximum being two thirds of the energizing voltage (typically 100 to 300mV at full scale). Fig.5shows how a DVM can he connected as a practical four - range ohmmeter.

+V2K

20K 2.7K

200K

2M

270

R x

- V

Fig.5. Five – range Digital Ohmmeter.

Objective : To acquaintance with Digital Voltmeter ( DVM ) .

Experimental procedure :

1. Connect the circuit as shown in Fig.6.

XDPRFH D1D2D3

RFLIn Hi

In Lo

Com

9M +V

2V

900K20V

Vin

100K

- V

Fig.6. Experimental circuit of a DVM .

2. Connect 0 to 20 V power supply between point 1 and 2 . and set the input voltage at zero.

3. Set the INHI switch at 2 V position and XDP switch at position 3.4. Set the input voltage at 0.5 V using a standard voltmeter and measure this voltage

by your assembled voltmeter.5. Repeat these procedure for other set of values.6. Compare these two sets of observations and comment on this result.7. Set the INHI switch at 20 V position.8. Repeat steps 4 to 6.

Objective :To acquaintance with Digital Ammeter ( DAM ) and Digital Ohmmeter .


RFLInLo

Com



+V990 Ohm

1K20mA 100 Ohm 9 Ohm

200 mAVin

1 Ohm

- VFig.7. Experimental circuit of a Digital Milliammeter.

2. Connect 0 to 20 V power supply between point 3 and 5 . and set the input voltage at zero.

3. Set the switch at 2 0 mA position .4. Set the current at 2mA using a standard milliammeter and measure this current

by your assembled milliammeter.5. Repeat these procedure for other set of values.6. Compare these two sets of observations and comment on this result.7. Connect 0 to 20 V power supply between point 4 and 5 . and set the input voltage at

zero.8. Set the switch at 2 0 0 mA position.9. Set the current at 20mA using a standard milliammeter and measure this current

by your assembled milliammeter.10. Repeat these procedure for other set of values.11. Compare these two sets of observations and comment on this result.

Objective :

To acquaintance with Digital Ohmmeter .


RFLInLo

Com



+V2K

20K 2.7K

200K

2M

270

R x

- VFig.8. Experimental circuit of Digital Ohmmeter.

2. Set the unknown resistance at position 1 and connect it between point 6 and 7 . 3. Set the switch SW 3 at Ohm position .4. Record your observation .5. Set another resistance ( say , at position 2 ) .6. Record your observation .7. Measure these resistance by a standard digital multimeter.8. Compare these two sets of observations and comment on this result.

XDPRFH D1D2D3

RFLIn Hi

In Lo

Com

OHMSW3

V / I

7107

COM INHI INLO RFL RFH

+

0 TO 20 V_

9M INHI 2V2V Vcc 20V900K20V RFL RFH

100K INLO

COM

VOLTMETER

OHM

SW3V / I

7107


+

0 TO 20 V_

1K 990 ohmVcc 20mA

9 Ohm 47K 100 OHM 200mA RFH 20 mA RFL1 Ohm 200 mA INLO2K MILLIAMMETER COM COM

OHMSW3V / I

7107


5 6 74 8 9 32 101 11

OHM

2K 2.7K +V

20K

270 RFL INLORxINHI COM

OHMMETER

EXPERIMENT-4

VOLTAGE-TO-CURRENT CONVERSION

Introduction : The commonest electrical standard is the 4 to 20 mA current loop . As its

name implies, this uses a variable current signal with 4 mA representing one end of the

signal range and 20 mA the other. The current loop is totally floating from earth (and will

not work correctly if an earth is applied to the signal lines). This gives excellent noise

immunity as common mode noise has no effect and errors caused by different earth

potentials around the plant are avoided. Because current, rather than voltage, is used, line

resistance has no effect .

Several display/control devices can be connected in series (as in Fig. 1 ), providing the total

resistance does not rise above some value specified for the transducer .

Transducer display / control

PV 4 – 20 mA MV

Current controlling device Current sensing device

(a)

Transducer

PV 4 – 20 mA

(b)

Fig. 1. The 4 to 20 mA current loop transmission system. (a) Principle of 4 - 20 mA current

loop. (b) Series connection of display/control devices.

ChartRecorder Display Control

Transducers using 4—20 mA can be current sourcing (with their own power supply. a~—

in-fig~ l.4a) or designed for two-wire operation where the signal wires also act as the

power supply connections .

The use of an offset zero (4 mA) has several advantages ( not least of which is the

provision of sufficient current for a two wire transducer to continue working at zero

output). If a zero voltage or current for tile bottom of the range was chosen, an open –

circuit or short-circuit line would look like a bottom-range signal . Any line fault on a 4—

20 mA line will cause a substantial negative signal which is easily detected at the controller

or display device . In addition, the signal is decidedly unipolar, giving no ambiguities

around zero, and obviating the need for a negative power supply which would be needed

to give a zero voltage or current output .

Although 4—20 mA is by far the commonest electrical standard , others may be

encountered. Among these are 10 – 50 mA and 1 – 5 V , again using an offset zero . Often 4 –

20 mA signals are converted to 1 – 5 V at the display device or controller by a series 250

ohm resistor .

Signal voltage transmission presents many problems. The series resistance between the

output of the signal conditioner and the load depends on the distance , the wire used the

temperature, arid how well the connections are made. Even a few millivolts of loss across

this series resistance could significantly alter the percentage error of the measurement .

Current, however, is the same everywhere in a series (transmission loop ) . Converting the

signal to a current and sending that current assures you that the load will receive all of the

signal (current) you sent. None will be lost because of line resistance or poor connections.

The type of voltage-to-current conversion you use depends on the load’s resistance and

whether the load is floating or tied to ground. A floating load is preferable. It allows you to

apply common-mode rejection techniques at the receiver to reduce the induced noise.

More on this later. However, you may have to drive the signal into a grounded load, either

for safety reasons or because the display and control electronics are built that way.

Floating Load

The simplest voltage-to-current converter is shown in Figure 2. It is actually only a

noninverting amplifier. The transmission loop and remote load into which the signal is

being driven form the upper part of the negative feedback loop. Analysis is as simple as the

circuit itself. Since the op amp is operating closed loop (with negative feedback), the

voltage at the noninverting input also appears at the inverting input. But this voltage is

across the lower resistor R. The current through that resistor is I.

_ I R wire

+Load

e in

R

I

Fig.2. Simple Voltage to Current converter.

Since no current (of significance) flows into or out of the inverting input, I must be want

the current in the current loop.

There are several points you must consider when using the circuit in Figure 2 . The

resistance in the transmission loop (RLOOP = Rwire + Rload) does not affect the amount of

transmitted current at all. The output voltage oh the op amp is affected by RLOOP .

VOUT = ( 1 + / R ) e in< VSAT

+ Vcc

Zero

1M _

Q1

+

e in 1M

IL Load

Span

(a)

I

I(B)

I(A)

e(A) e(B) e in

Fig.3. Offset Voltage to Current Converter ( a ) Circuit ( b) Transfer curve .

You must keep RLOOP small enough to keep the op. amp out of saturation.

An offset voltage-to-current converter is shown in Figure 3. The noninverting amplifier of

Figure 2 has been replaced by a noninverting summer. The output current now is jointly

determined by the input voltage e in and the reference voltage e ref .

The input voltage-to-output current transfer curve is shown in Figure 3b. It is linear and

can be positioned anywhere in the upper two quadrants by specifying e(A), 1(A) and e(B),

1(B) (the two endpoints of the line). Given that an input voltage of e(A) will produce a

current of 1(A) and that an input voltage of e(B) will produce a current of 1(B) .

Grounded Load

If you need to drive current into a load that is connected to ground, a difference amplifier is

needed. This is shown in Figure 4. Resistors R1, R2, R3, and R4 are all equal. giving a gain of 1.

A resistor RShas been placed between the output and the load. Also, R4 has been connected

to the load rather than to ground.

R3

R1 _ I

Rs

e1 R2 +

R Load

e2

R4

R1 = R2 = R3 = R4 = R

Fig.4. Voltage to Current converter driving a grounded load .

A difference amplifier is shown. However, you can ground e1 for a non – invertingconverter

or ground e2 for an inverting converter. Or you could use one input for the signal, the other

for a zero (offset) and RS for the span adjust. In fact the difference amplifier could be

replaced by an instrumentation amplifier to the left side of R and the reference terminal to

the right .

100K

Zero +Vcc

_

100K 100

+

e in 100K Span R Load

100k

Fig.5. Voltage to Current Converter

EXPERIMENTAL PROCEDURE :

Voltage to Current Converter ( Floating Load ) :

1 . Connect the circuit as shown in Fig 6 + Vcc

Zero

1M _

Q1

+ mA

e in 1M

IL R Load

0 – 5 V V

Span

Fig.6. Experimental circuit for Voltage – To – Current Converter when Load is floating .2. Zero , Span and Input Voltage ( 0 – 5 V ) knobs set in anti – clockwise direction.3 .Switch on the trainer supply .4. Voltmeter shows input voltage zero , adjust Zero setting knob to Milliammeter shows 4 mA or nearly 4 mA .5. Set input voltage at 5 V and adjust Span setting knob to Milliammeter shows 20 mA .6. Follow the same procedures as in steps 4 and 5 alternatively . We get , output load current 4 mA at 0 V and 20 mA at 5 V and do not disturb the Zero and Span adjustment pot.7. Set the input voltage 0V and measure the output Current in mA .8. Increase the input voltage 0.5 V in step upto 5 V and measures the output load currents in mA .9. Record your observation in Table I .10 . Draw a graph Input Voltage , V( in) Vs. Output load Current I(L) in mA .11. Comment on Linearity of the curve.Voltage to Current Converter ( Grounded Load ) :

100K

Zero +Vcc

_

100K 100 mA

+

+ 100K Span R Load

V

_

100K

Fig.7. Experimental circuit for Voltage – To – Current Converter when Load is Grounded .

1 . Connect the circuit as shown in Fig 7.

2. Follow the same procedure as Voltage – to - Current Converter ( Floating Load ) .

No.of Obs. Input Voltage Output Current in Volt in mA

EXPERIMENT-5

Current to Voltage Convertor

Introduction : The commonest electrical standard is the 4 to 20 mA current loop . As its

name implies, this uses a variable current signal with 4 mA representing one end of the

signal range and 20 mA the other. The current loop is totally floating from earth (and will

not work correctly if an earth is applied to the signal lines). This gives excellent noise

immunity as common mode noise has no effect and errors caused by different earth

potentials around the plant are avoided. Because current, rather than voltage, is used, line

resistance has no effect .

Several display/control devices can be connected in series (as in Fig. 1 ), providing the total

resistance does not rise above some value specified for the transducer .

Transducer display / control

PV 4 – 20 mA MV

Current controlling device Current sensing device

(a)

Transducer

PV 4 – 20 mA

(b)

Fig. 1. The 4 to 20 mA current loop transmission system. (a) Principle of 4 - 20 mA current

loop. (b) Series connection of display/control devices.

Transducers using 4—20 mA can be current sourcing (with their own power supply. a~—

in-fig~ l.4a) or designed for two-wire operation where the signal wires also act as the

power supply connections .

The use of an offset zero (4 mA) has several advantages ( not least of which is the

provision of sufficient current for a two wire transducer to continue working at zero

output). If a zero voltage or current for tile bottom of the range was chosen, an open –

circuit or short-circuit line would look like a bottom-range signal . Any line fault on a 4—

20 mA line will cause a substantial negative signal which is easily detected at the controller

or display device . In addition, the signal is decidedly unipolar, giving no ambiguities

around zero, and obviating the need for a negative power supply which would be needed

to give a zero voltage or current output .

Although 4—20 mA is by far the commonest electrical standard , others may be

ChartRecorder Display Control

encountered. Among these are 10 – 50 mA and 1 – 5 V , again using an offset zero . Often 4 –

20 mA signals are converted to 1 – 5 V at the display device or controller by a series 250

ohm resistor .

Once the current signal gets to the place where is to be used , it must be converted back

into a voltage . You can do this very simple with a resistor .For a ground reference load ,

this is all you need – well , almost . Look at Fig 3. The transmitter current is converted into

a voltage by R . However this may not provide precisely the endpoints (zero and span) you

want . To provide you with the adjustment. U2 and U3 is the standard zero and span

converter The grounded load converter has several problems. There must be ground

return for the current between the transmitter and receiver. Any resistance in this line will

cause an additional voltage drop. Although this error may he calibrated out , any variation

in the ground return resistance will cause a variation in signal . Even worse , there is often

several volts of difference between ground points in .manufacturing facility . This is usually

50 Hz and varies randomly as machines are turned on and off. This variation in ground

potential appears to be part of the signal to the receiver (display and controller). The result

is totally unpredictable, and unacceptable behavior in the control system.

Zero

-V

250K 330K 2.2K

I _ 2.2K

100K -

+ + V0

R

68K

1.1K

Fig.3. Ground – Referenced Current – to –Voltage Converter.

The solution is to use a floating load. Current is sent to and returned from , the load along a

twisted pair of wires. Any noise coupled onto this wires appear at both ends of the load

simultaneously. If both ends of the load are raised or lowered by precisely the same

voltage, there is no net difference in potential across the load . So the common-mode noise

is rejected. Similarly, any difference in potential between the ground of the transmitter and

the ground of the receiver will show up on both lines sent to the floating load. This, too, is

common mode, producing no difference across the load. The electronics needed to

condition the voltage from a floating load are shown in Fig 4.The transmitted current is

converted to a differential voltage by RSPAN Op. Amp. U1 and resistors Ri and Rf form a

differential amplifier It buffers the differential voltage across RSPAN amplifies it by Rf / Ri

and provides a ground – referenced output .

22K

+ I 2.2K

_

50

Span V0

2.2K +

_

10K

Zero

Fig.4. Floating Current to Voltage Converter .

EXPERIMENTAL PROCEDURE :

Voltage to Current Converter ( Floating Load ) :


+ Vcc

Zero

1M _

Q1

+ mA

e in 1M

IL R Load

0 – 5 V V

Span

Fig.5. Experimental circuit for Voltage – To – Current Converter when Load is floating .

2. Zero , Span and Input Voltage ( 0 – 5 V ) knobs set in anti – clockwise direction.

3 .Switch on the trainer supply .

4. Voltmeter shows input voltage zero , adjust Zero setting knob to Milliammeter shows 4 mA or nearly 4 mA .

5. Set input voltage at 5 V and adjust Span setting knob to Milliammeter shows 20 mA .

6. Follow the same procedures as in steps 4 and 5 alternatively . We get , output load current 4 mA at 0 V and 20 mA at 5 V and do not disturb the Zero and Span adjustment pot.

7. Set the input voltage 0V and measure the output Current in mA .

8. Increase the input voltage 0.5 V in step upto 5 V and measures the output load currents in mA .9. Record your observation in Table I .

10 . Draw a graph Input Voltage , V( in) Vs. Output load Current I(L) in mA .

11. Comment on Linearity of the curve.

Voltage to Current Converter ( Grounded Load ) :

100K

Zero +Vcc

_

100K 100 mA

+

+ 100K Span R Load

V

_

100K

Fig.6. Experimental circuit for Voltage – To – Current Converter when Load is Grounded .1 . Connect the circuit as shown in Fig 6.

2. Follow the same procedure as Voltage – to - Current Converter ( Floating Load ) .Current To Voltage Converter ( Floating input )


22K

+ mA 2.2K

_

50

Span

2.2K + V0

_

10K

Zero

Fig.7. Experimental circuit for Current to Voltage Converter when input current is Floating .

2. Zero , Span and Input current ( 0 – 5 V ) knobs set in anti – clockwise direction.

3 .Switch on the trainer supply .

4. Milliammeter shows input current 4 mA , adjust Zero setting knob to voltmeter shows 0 V or nearly zero.

5. Set input current at 20 mA and adjust Span setting knob to Voltmeter shows 5 V.

6. Follow the same procedures as in steps 4 and 5 alternatively . We get , output Voltage 0 V at 4 mA and 5 V at 20 mA and do not disturb the Zero and Span adjustment pot.

7. Set the input Current 4 mA and measure the output Output voltage .8. Increase the input Current 1mA in step upto 20 mA and measures the output Voltage .9. Record your observation in Table I .10 . Draw a graph Input Current I(in) in mA Vs. Output Voltage V(0) in Volt .11. Comment on Linearity of the curve.

Current To Voltage Converter ( Grounded input )

Zero

-V

250K 330K 2.2K

_ 2.2K

100K -

+

R V0

68K

1.1K

Fig.8. Experimental circuit for Ground – Referenced Current – to –Voltage Converter.


2. Follow the same procedure as Voltage – to - Current Converter ( Floating Load ) .

Table I

No.of Obs. Input Current Output Voltage in mA in volt

EXPERIMENT-6

PHASE LOCKED LOOP

Introduction :

PHASE LOCKED LOOP (PLL) has emerged as one of the fundamental building block in electronic technology. it is used for the frequency multiplication, FM stereo detector, FM demodulator, frequency shift keying decoders, local oscillator in TV and FM tuner.

The block diagram of a PLL is shown in the Fig.1. It consists of a phase detector, a LPF, and a voltage controlled oscillator (VCO). The phase detector or comparator compares the input frequency, fin, with feedback frequency, f0ut (output frequency). The output of the phase

detector is proportional to the phase difference between, finand f0ut. The output voltage of the phase detector is a DC voltage and therefore, is often refers to as error voltage. The output of the phase detector is then applied to the LPF, which removes the high frequency noise and produces a DC level. The DC level, in-tern is the input to the VCO.

fin fout

fout

Fig.1 . Block diagram of Phase locked Loop.

The output frequency of the VCO is directly proportional to the input DC level. The VCO frequency is compared with the input frequencies and adjusted until it is equal to the input frequency. In short, PLL keeps its output frequency constant at the input frequency.

Thus, the PLL goes through 3 states,1 Free running state.2. Capture range/mode.3. Phase lock state.

Before input is applied, the PLL is in the free running state. Once the input frequency is applied, the VCO frequency starts to change and the PLL is said to be the capture range/mode.

The VCO frequency continues to change (output frequency) until it equals the input frequency and the I’LL is then in the phase locked state. When phase is locked, the loop tracks any change in the input frequency through its repetitive action.

IC Version of PLL Today, the I’LL is even available as a single package. and examples are 560, 561, 562, 564, 565 and 567. These are all monolithic ICs. These differs mainly in operating frequency range, power supply requirements, etc.

Characteristics of 565 IC

1. Operating frequency : 0.001 Hz to 500 kHz.2. Operating voltage: ± 6V to ± 12V

Phase detector Low Pass Filter Amplifier

VCO

3.Input level required for tracking: 10 mV (rms) to 3V(pp).4. Input impedance : 10 K ohm5. Output sink current : 1 mA (typical)6. Output source current : 10 mA (typical)

Frequency Multiplication Using PLL

The frequency divider is inserted between the VCO and the phase detector in the feedback path. Since the output of the divider is locked to the input frequency, fin the VCO is actually running at the multiple of the input frequency and hence the name multiplier. The divider-by-N network is a modulo N (MOD-N) binary counter. A proper divide-by-N network can obtain the desired amount of multiplication. Where N is an integer.

fin fout

fout

Fig.2. Block diagram of frequency Multiplication using PLL.

Objectives :

1. To become familiar with the phase Locked Loop ( PLL ) and its major subsystem building blocks.

2. To study the static and dynamic behavior of the phase locked loop.

Test Equipment :

Phase detector Low Pass Filter Amplifier

VCOFrequency Divider Network

VCO & PLL TRAINER

Function Generator

Dual Trace Oscilloscope

Digital Multimeter

Frequency Counter


VCO Static Tests

1. Connect the circuit as shown in Fig.3 . Switch ON the power supply. Monitor the VCO output voltage at TP4 using the oscilloscope. Measure and record the waveform of the VCO output signal , noting the amplitude and frequency.

2. Note the effect on the free running VCO output waveform by introducing each of the following changes , one at a time . Use a frequency counter to measure the frequency at TP4 and observe the signal with an oscilloscope . Make sure that each alteration is restored back to its original form before proceeding to the next step.(a) Decrease the timing resistor ,R3 to 2.2 K ohm.(b) Increase the timing capacitor , C1 to 0.022 uF(c) Load the VCO output with a capacitive load by placing a series RC load between TP2

and ground . Let R = 680 ohm and C = 0.001 uF .

3. Measure the reference dc voltage level at the phase detector output by connecting the scope through 10 : 1 probe ( if necessary ) to TP2. Apply a dc voltage level equal to the reference to TP5 ( no coupling capacitor ) . Increase and decrease the applied voltage above and below the reference voltage level in 0.5 V . At each setting , measure the resulting VCO output frequency . Disconnect the dc voltage before proceeding .

Vcc -Vcc

TP2 0.1uF TP1

+VccTP5 68033K 680

10 1 2

6 3

565

5

4

5K

4.7KTP610uF TP3 TP4 33K VCO o/p0.01uF 680

5K 0.001uF0.1uF0.1uF 0.01uF

+Vcc -Vcc

Fig.3. Experimental circuit for VCO Static Test.

Pin 2 and 3 : Phase Detector input

Pin 4 : VCO output

Pin 9 :VCO Capacitor

Pin 8 :VCO Resistance

Pin 7 : VCO input

Pin 6 : Detected DC reference

VCO Dynamic Tests

4. Connect the function generator at TP6 . Apply a 2 KHz ,4 Vpp , sine wave as the VCO input voltage at TP6. Sketch the resulting VCO output waveform displayed at TP4 . You are observing an FM waveform.

10 1 2

6 3

565

5

4

(a) Carefully increase and decrease the amplitude of the function generator and note the effect on the FM output signal at TP4. Return back 2 K Hz before proceeding.

(b) Carefully increase and decrease the frequency of the Function Generator and note the effect on the FM output signal at TP4 . Return to 2 KHz before proceeding .

Vcc -Vcc

TP2 0.1uF TP1

+VccTP5 68033K 6805K

4.7KTP610uF F.G TP3 TP4 33K VCO o/p0.01uF 680

5K 0.001uF0.1uF0.1uF 0.01uF

+Vcc -Vcc

Fig.4. Experimental circuit for VCO Dynamic Test.

F.G : Function Geneartor


Pin 4 : VCO output

10 1 2

6 3

565

5

4

7 8 9



Pin 7 : VCO input


Phase – Detector Static Tests

5. Build the phase detector circuit shown in Fig.5 . Connect the test equipment to the phase detector test circuit shown in Fig.6. Use the scope to monitor the input voltage at TP1 on channel A and to monitor the VCO output voltage at TP4 on channel 2 . Use a Digital Voltmeter to monitor the difference voltage between TP2 and TP3 of the phase detector .

6. With no voltage applied at TP4 , measure the difference voltage with Digital Voltmeter . This value is the reference level of the phase detector output . Also measure the free running frequency of the VCO by measuring the frequency of the VCO output signal at TP4 using the oscilloscope.

7. Apply a 0.5 Vpp square wave at frequency approximately equal to that of the VCO . Vary the frequency of the input signal and you should see that the VCO output signal will ‘track’ the frequency of the input signal as long as it is fairly close the free running frequency . Also the difference voltage measured with the digital multimeter should vary as long as tracking is taking place . Adjust the frequency of the input voltage so that the difference voltage equals the reference voltage value measured in step 6 . Record the waveform of the input voltage and the VCO output signal under these conditions . Note the amplitudes , frequencies and approximate phase difference between the two waveforms.

8. Increase the frequency of the input voltage to 5 % , above the original value . Record the approximate phase difference between ? and VCO output voltage . Repeat 10 % above its original frequency.

9. Repeat step 8 except decrease the frequency of the input voltage by 5 % and 10 %.

10. Now increase the frequency of Vin up to the frequency at which it loses its lock on the VCO output signal . When it loses lock , the VCO output signal returns to its free running frequency and the difference voltage between TP2 and TP3 returns to its reference value determined in step 6 . Measure and record its upper and lower frequencies where it loses lock . A few trials are usually necessary in order to obtain consistent results.

This range of frequencies between the upper and lower measured frequencies is referred to as the PLL’s tracking range.

11. Notice that the PLL also provides hysteresis at both upper and lower limits of its tracking range . In particular , you should notice that when the PLL loses its lock at the high end of the tracking range, you need to decrease the frequency of Vin a bit lower before the PLL locks back up . The frequency at which it locks up again is referred to as the upper end of the PLL ‘s capture range . The same hysteresis effect occurs at the low end of the tracking range . Measure the upper and lower limits of the capture range . To determine if lockup is occurring , observe the level of the difference voltage between TP2 and TP3 rather than checking the stability of the VCO output signal . Again , several attempts will be necessary to yield consistent results. Record your results.

Vcc -Vcc

TP2 0.1uF TP1-+Vcc

10 1 2

6 3

565

5

TP5 68033K 6805K

4.7KTP610uF TP3 TP4 33K + VCO o/p0.01uF 680

5K 0.001uF0.1uF0.1uF 0.01uF

+Vcc -Vcc

Fig.5. Experimental circuit for Phase Detector test circuit.


Pin 4 : VCO output



Pin 7 : VCO input


TP3TP1

TP4 TP2

10 1 2

6 3

565

5

Function GeneratorPhase Detector

(Fig.4)VOM

Ch.A Ch.B

Oscilloscope

Fig.6. Phase Detector static test circuit configuration.

Report :

1. Summarize the effects of each of the changes made in step 2 . Comment on the stability of a PLL‘s VCO when in the free running state.

2. Plot the VCO output frequency versus dc input voltage for the measurements made in step 3 . From your graph determine the VCO’s deviation constant by determining the slope of the resulting linear graph .

Δ f (VCO) f max – f min

Kf = = Δ (VTP4A) Vmax – V min

3. Explain the difference between the two frequency – modulated waveforms observed in step 4. What characteristics of the observed FM waveform was changing in each case ?

4. Plot the relative phase difference Vin and the VCO output voltage versus frequency using the results of steps 8 and 9 of the phase detector static tests . From your graph determine the phase detector’s deviation constant by determining the slope of the resulting linear graph .

ΔΦ Φmax - Φmin

KΦ = -------- = -------------- Δ f (VCO) f max – f min

EXPERIMENT-7

8 CHANNEL DAS

1) INSTALLATION OF SOFTWARE FOR SERIAL PORT

A) Insert the 8 Channel CD

B) Copy all files from CD to a folder in hard disk.

2) USING THE SOFTWARE

A) SETTING THE PORT

A) Before any data acquisition experiment one has to set the port by selecting the menu PORT. Port configuration setup will appear. Select Port in which DAS hardware is connected. Don’t change other port settings. Then press OK.

(Fig. 1)B) CALIBRATION FACTORIt works in two modes. First one can set additive constant, multiplicative constant and

unit of physical parameters measured channel wise to get the actual physical values of

the acquired data (Fig 2).

(Fig. 2)

Second mode uses a table. One can use maximum 50 points table. Each table data has to

be stored in respective file named as ch1.txt, ch2.txt, ch3.txt etc. Select use table

checkbox against respective channels. During data acquisition the respective table

behave as lookup table. The actual physical parameter will be calculated from this

calibrated lookup table.

One can prepare the table with any text file editor. The data format will be like ‘Each

line should have one set of data. First data will be the voltage then a comma (,), next will

be the corresponding physical value (e.g. 1.20,425)’.

Alternatively one can prepare the table using EDIT TABLE button and keeping the

system online. The current voltage is always shown. In the respective edit box enter the

corresponding physical value. Then press ADD button. The data set will be shown in the

left grid. Always add data in increasing order of voltage. After adding all the data points

in the physical manner for the tables press the SAVE button. If you make any mistake

during table preparation you can manually edit data of corresponding text files in text

editor. But be careful about the structure of the data in text files. The details are shown

in (Fig 3).

One can set also set the line color of the graph.

(Fig. 3)

C) SAMPLING FREQUENCY – Sets the samples collected per second. Maximum could set to 20 samples per second.

D) RESOLUTION – One can select 2/4/8 bit resolution data collection. This option shows clearly the quantization effect of analog to digital conversion. Higher the bit resolution more accurate the digital data. Fig 4.

This DAS hardware works in the range 0-5V. Now selecting the 2 bit resolution, the entire range can have 4 division i.e. it will show 0V, 1.25V, 2.5V, 3.75V, 5V (minimum resolution 1.25V) as the input analog changes from 0 to 5 V.

Similarly selecting 4 bit, the entire range will have 16 division with minimum resolution 0.3125V. Here one can observe the values rounded to two decimal places.

8 bit gives minimum resolution 0.020V. The total range breaks into 256 division.

(Fig. 4)

E) START – Start Menu will start data acquisition with set sampling frequency and the screen will look like the following. Fig 5.The x-axis represents the real time graph. Y-axis represents the physical parameters.

(Fig. 5)

F) STOP – Stop menu will stop the data acquisition.

Large display of channel data

To get enlarged view of any channel take the mouse over the channel window. Press the right button and select ZOOM. You will get enlarged view. The data presented in enlarged view will be from start of the experiment to the point of time of selecting zoom.

Max No. of point in online graph is limited to 50 for clarity.

When data acquisition is going on each channel window display maximum 50 points at a time. When the total data exceeds 50 the each channel window refreshes. Though the old data can be viewed by right clicking the mouse and dragging the screen rightside.

G) DATA – Data will display the data acquired in table format as shown in Fig. 6.The last appended data will go to bottom of table.

(Fig. 6)

H) GRAPH – Graph menu will change the display to default real time graphical display.

I) SAVE - Save menu will open the save dialog box (Fig 7.) and allows data to be saved in a text (ASCII) file with the given filename. The data are in comma delimited format. This data can be imported in EXCEL.

(Fig. 7)

SAVE dialog box

I) OPEN – Open menu will open the open dialog box similar to save dialog box. Already saved data can be opened with this.

J) X-Y PLOT – This menu will allow x-y plot. Select the appropriate channel as x-axis and y-axis the press the draw button (Fig 8.).

(Fig. 8)

K) STATISTICAL CALCULATION - Various statistical parameters mean, std deviation, variance, Cp, Cpk and Histogram are displayed in this panel. The corresponding formula are given below Fig 9.

Formulas for calculating different statistical parameter

Mean, = 1 / n x i, where x i is the data point and n is the no. of data points.

Standard Deviation, = 1 / n (n x2i - x ix i)

Variance = 2

C p and C p k are two parameters from Statistical Quality Control. It describes the ongoing process ability. To calculate them one has to specify upper limit (UL) and lower limit (LL). Let us illustrate this with example. Suppose we want to measure ability of a furnace temperature controller to maintain a constant temperature say 250oC. No controller can maintain it to a fixed value. It will vary over the range. We specify 255o and245o to be the UL and LL.Now Cp of the process can be calculated as Cp = (UL – LL) / ( 6)To calculate Cpk we have calculate other two parameter asCpku = (UL - ) / ( 3);

Cpkl = ( - LL) / (3);Now Cpk = Min(Cpku , Cpkl) i.e. minimum of two values Cpku or Cpkl

(Fig. 9)

Sample program in C to calculate the statistical parameters#include <stdio.h>#include <math.h>

main(){

float a;int no, i;float sum, sum2x, x, cpuu, cpul, usl, lsl, sd, var, mean, cp, cpk;

printf("Please give the no. of data points : ");scanf("%d", &no);sum = 0;sum2x = 0;for(i = 0; i < no; i++)

{printf("Data %d ", i + 1);scanf("%f", &a);sum += a;sum2x += a*a;

}printf("Give upper limit");scanf("%f",&usl);printf("Give lower limit");scanf("%f",&lsl);

if(no * sum2x > sum*sum){

mean = sum / no;sd = sqrt(no * sum2x - sum * sum) / no;var = sd * sd;

cpuu = (usl - mean) / (3 * sd);cpul = (mean - lsl) / ( 3 * sd);

if (cpuu < cpul)cpk = cpuu;

elsecpk = cpul;

cp = (usl - lsl) / (6 * sd);

printf("Mean = %f, sd = %f, variance = %f, cp = %f, cpk = %f", mean, sd, var, cp, cpk);

}}

L) SPECTRUM ANALYSIS : FFT can be applied to any channel data collected to get the spectrum. Fig 10 shows data collected in channel 2. The data contains two sin wave summed. Freq and amplitude of one is double of the other.

Fig 10

Fig 11 shows the spectrum analysis. The graph shows power spectrum of two sine waves obtained from FFT.

Fig 11

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