Transducers - Copy Kunal

8/13/2019 Transducers - Copy Kunal

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PRESENTATION

ONSENSORS(TRANSDUCERS)

BY:PRATISH SHARMA (GME/115601)

SUBHASH KUMAR (GME/115602)

KUNAL DUTT SHARMA (GME/115603)


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INTRODUCTION OF TRANSDUCERS

A transducer is a device that convert one form of energyto other form. It converts the measurand to a usableelectrical signal.

In other word it is a device that is capable of converting

the physical quantity into a proportional electricalquantity such as voltage or current.

Pressure Voltage


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BLOCK DIAGRAM OF TRANSDUCERS

Transducer contains two parts that are closely related toeach other i.e. the sensing element and transductionelement.

The sensing element is called as the sensor. It is deviceproducing measurable response to change in physicalconditions.

The transduction element convert the sensor output tosuitable electrical form.


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CHARACTERISTICS OF TRANSDUCERS

1. Ruggedness2. Linearity

3. Repeatability

4. Accuracy

5. High stability and reliability6. Speed of response

7. Sensitivity

8. Small size


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CLASSIFICATION OF TRANSDUCERS

The transducers can be classified as:

I. Active and passive transducers.II. Analog and digital transducers.III. On the basis of transduction principle used.

IV. Primary and secondary transducer.V. Transducer and inverse transducer.


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Active transducers :

These transducers do not need any external source of power

for their operation. Therefore they are also called as self

generating type transducers.

I. The active transducer are self generating devices whichoperate under the energy conversion principle.

II. As the output of active transducers we get an equivalent

electrical output signal e.g. temperature or strain to electric

potential, without any external source of energy being used.

ACTIVE AND PASSIVE TRANSDUCERS


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Piezoelectric Transducer


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CLASSIFICATION OF ACTIVE TRANSDUCERS


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Passive Transducers :

I. These transducers need external source of power for theiroperation. So they are not self generating type transducers.

II. A DC power supply or an audio frequency generator is used

as an external power source.

III. These transducers produce the output signal in the form ofvariation in resistance, capacitance, inductance or some other

electrical parameter in response to the quantity to be

measured.


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CLASSIFICATION OF PASSIVE

TRANSDUCERS


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PRIMARY AND SECONDARY

TRANSDUCERS

Some transducers contain the mechanical as well as electricaldevice. The mechanical device converts the physical quantity

to be measured into a mechanical signal. Such mechanical

device are called as the primary transducers, because they deal

with the physical quantity to be measured.

The electrical device then convert this mechanical signal into

a corresponding electrical signal. Such electrical device are

known as secondary transducers.


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CLASSIFICATION OF TRANSDUCERSAccording to Transduction Principle


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CLASSIFICATION OF TRANSDUCERSTransducer and Inverse Transducer

TRANSDUCER:

Transducers convert non electrical quantity to

electrical quantity.

INVERSE TRANSDUCER:

Inverse transducers convert electrical quantity to a

non electrical quantity


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THERMISTOR

Thermistor is a contraction of a term thermal resistor.Thermistors are temperature dependent resistors. They are

made of semiconductor material which have negative

temperature coefficient of resistivity i.e. their resistance

decreases with increase of temperature.Thermistor are widely used in application which involve

measurement in the range of 0-60C.Thermistors are

composed of sintered mixture of metallic oxides such as

manganese, nickle, cobalt, copper, iron and chromium.


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The thermistor may be in the form of beads, rods anddiscs.

The thermistor provide a large change in resistance for

small change in temperature. In some cases the

resistance of themistor at room temperature maydecreases as much as 6% for each 1C rise in

temperature.


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Thermocouples

See beck Effect

When a pair of dissimilar metals are joined at one end, and there is a

temperature difference between the joined ends and the open ends,

thermal emf is generated, which can be measured in the open ends.

This forms the basis of thermocouples.


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STRAIN GAUGE

The most common type of strain

gauge consists of an insulating flexible

backing which supports a metallic foil

pattern. The gauge is attached to the

object by a suitable adhesive. As the object is deformed, the foil is

deformed, causing its electrical

resistance to change.

This resistance change, usually

measured using a Wheatstone bridge.

A strain gauge is a device used to measure strain on an object

Strain gauge measuring growth of

a crack in a wall

Close up of strain gauge


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HOW STRAIN IS MEASURED1.R= l/AWhere is resistivity

l is lengthA is area of cross section

For quarter bridge

2.G=dR/(R*)Where G is the gauge factor

dR is change in resistance

R is resistance

is strain

3.Vo=G**Vs/4

Where Vo is output voltageVs is supply voltage

4.Stress=E*

Where E is ELASTIC MODULAS


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OPTICAL ENCODERS

It is an electro-mechanical device that converts theangular position or

motion of a shaft or axle to an analog or digital code.

This digital signal can be used to determine position, direction and velocity

of shaft.

These are of two types:

1. Absolute encoders:- They give actual angular

position. An absolute encoder generates aunique code for each position.

2. Incremental encoders:- They detect changes in

rotation from some datum position. Forincremental encoders, each mechanical position is

uniquely defined. The current position sensed is

only incremental when compared to the last

position sensed.


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WORKING

Beam of light passes through slots in disc andis detected by sensor

A pulsed output is generated by the sensor.

Number of pulses being proportional to angle

turned by the disc.Thus the angular position of the disc and hence

the shaft rotating it can be determined.

The offset of the two concentric track enables the

direction of rotation to be determined


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Resolution of optical encoders

It is determined by number of slots on the disc

If there are 60 slots in one revolution of disc

Resolution =360/60=6

In case of absolute encoders it gives output in form of binary no of several

digits each number representing a particular angular position.

So a typical encoder has 10 to 12 tracks

Number of position that can be detected =2^10 ie 1024

Resolution =360/1024=0.35


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HALL EFFECT SENSOR:PRINCIPLE

A Hall effect sensoris a transducer that variesits output voltage in response to a magnetic

field. Hall effect sensors are used for proximity

switching, positioning, speed detection, and

current sensing applications.

When a beam of charged particles passes

through a magnetic field, forces act on the

particles and the beam is deflected from its

straight line path.


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HALL EFFECT SENSOR:ADVANTAGEIt can be operated as a switchIt can be operated upto 100kHz

Cost is less than other mechanical switches

It does not suffer from contact bounce

because a sequence of contacts are usedrather than a single contact.

It will not be affected by environmentalcontaminants. Therefore it can be used

under severe conditions.It can be used as position, displacement andproximity sensors.


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HALL EFFECT SENSOR:APPLICATION

Fuel level indicator

In brushless D.C motor


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LINEAR VARIABLE DIFFERENTIAL

TRANSFORMER(LVDT)

AN LVDT transducercomprises a coil former on towhich three coils are wound.

The primary coil is excitedwith an AC current, thesecondary coils are woundsuch that when a ferrite coreis in the central linear

position, an equal voltage isinduced in to each coil.

The secondary are connectedin opposite so that in thecentral position the outputsof the secondary cancels

each other out.


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The excitation is applied to the primarywinding and the armature assists theinduction of current in to secondarycoils.

When the core is exactly at the center

of the coil then the flux linked to boththe secondary winding will be equal.Due to equal flux linkage thesecondary induced voltages (eo1 &eo2) are equalbut they have opposite

polarities. Output voltage eo istherefore zero. This position is callednull position


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Now if the core is displaced from its null

position toward sec1 then flux linked to sec1

increases and flux linked to sec2 decreases.

Therefore eo1 > eo2 and the output voltage ofLVDT eo will be positive

Similarly if the core is displaced toward sec2

then the eo2 > eo1 and the output voltage ofLVDT eo will be negative.


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RESISTANCE THERMOMETER Resistance of metal increase with increases in

temperature. Therefore metals are said to have apositive temperature coefficient of resistivity.

Fig shows the simplest type of open wire constructionof platinum rsistance thermometer. The platinumwire is wound in the form of spirals on an insulatingmaterial such as mica or ceramic.

This assembly is then placed at the tip of probe

This wire is in direct contact with the gas or liquidwhose temperature is to be measured.


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The resistance of the platinum wire changes with thechange in temperature of the gas or liquid

This type of sensor have a positive temperaturecoefficient of resistivity as they are made from metals

they are also known as resistance temperaturedetector

Resistance thermometer are generally of probe typefor immersion in medium whose temperature is to be

measured or controlled.


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Thank you

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Transducers - Copy Kunal