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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