Transducer Device when activated from one form energy converted to another quantity orDevice which converts one physical quantity or condition to another

Physical quantity heat , intensity of light, flow rate, liquid level, humidity etc

Sensor : sense physical quantity

Classification of transducersBased on principle of transductionActive & passiveAnalog & digitalInverse transducer

Based on principle usedThermo electricMagneto resistiveElectro kineticOptical

Passive transducerDevice which derive power reqd. for transduction from auxiliary power source - externally poweredEg : resistive, inductive, capacitiveWithout power they will not work

Active transducerNo extra power reqd. to produce I/pSelf generatingDraw power from input appliedEg. Piezo electric xtal used for accelartion measurement

Analog transducer convert I/p quantity into an analog o/p Analog o/p- a continuous fn. Of timeEg. Strain gauge, L VDT, thermocouple

Digital transducerConverts I/p into an electrical o/p in the form of pulses

Inverse transducerWhich converts electrical signal to physicalquantity

Transducer for pressure measurementWhat is pressure? force/ unit areaUnit (N/sq.m) PaPressure measured can be absolute , gauge or differential depending on type of reference

Types of pressure transducersGravitational eg : manometerElastic force converted to strain eg. Diaphragm, capsule, bellows, bourdon tubes

DiaphragmCommon pressure sensing elastic elementThin circular plate stretched & fastened at its peripheryMade of elastic alloys of bronze,phosphor bronze, stainless steel or alloys like Monel, Nickel span -C

Structure flat or corrugated

Top view of flat type

Top view of corrugated type

Flat type high natural frequency Corrugated for large deflections

Capsule

CapsuleTwo corrugated metal diaphragms sealed together at peripheryForms a shell like structureOne diaphragm has a port at centre to admit pressure to be measuredOther diaphragm linked to a moveable mechanical part.

Capsule Displacement proportional to difference b/w outer & inner pressure.

Bourdon tubes

curved or twisted metallic tubes with elliptical cross sectionSealed at one endTends to straighten when pressure applied.Angular sensitivity proportional to pressure applied

Spirial bourdon tubes

Bourdon tubes C type

Helical typeTube in the form of helix

Bourdon tubeMore sensitive to shock & vibrationsGood repeatability

Bellows

BellowsThin walled cylindrical sheets with deep convolutions sealed at one endSealed end moves axially when pressure is appliedNo. of convolution s vary from- 2 to 50 depends on range, operating tempUsed for low pressure measurement

Bellows displacement y = 2.n. A q P Rx 2 /( Et 2 .) where n no. of convolutions A q- effective area Et - youngs modulus of elasticityRx radius of diaphragmP pressure ie, Y P

Resistive typeEg. Strain gauge

Capacitive

Inductive typeEg. LVDT

Measurement of velocityVelocity linear or angular

Linear velocityElectromagnetic transducersO/p voltage E = /t = N I/ R2 . dR/dt where N I/ R2 is a constant R- reluctance so E proportional to reluctance R proportional to air gap & air gap proportional to velocity

Types Moving coilMoving magnetic

Angular velocityTachometer - typesMechanical ElectricalMHD sensor magneto hydrodynamic sensor highly sensitiveHigh precision

Transducer for vibrationVibrations give early warning of impending conditions which may develop &vlead to complete failure & destruction of equipmentUsed in power plants, turbines

Most vibrations are sinusodial in natureGot amp & freq.Amp gives displacementBy measuring displacement, velocity or acceleration - vibrations measured

Vibration transducerAccelometer measures shock or vibration Pot type or LVDT type

Pot type accelrometer

LVDT accelorometer

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