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Transducer. Device when activated from one form energy converted to another quantity or Device which converts one physical quantity or condition to another. Physical quantity – heat , intensity of light, flow rate, liquid level, humidity etc
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Transducer Device when activated from one form energy converted to another quantity or Device 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 transducers • Based on principle of transduction • Active & passive • Analog & digital • Inverse transducer
Based on principle used • Thermo electric • Magneto resistive • Electro kinetic • Optical
Passive transducer Device which derive power reqd. for transduction from auxiliary power source - externally powered Eg : resistive, inductive, capacitive Without power they will not work
Active transducer • No extra power reqd. to produce I/p • Self generating • Draw power from input applied • Eg. Piezo electric x’tal used for accelartion measurement
Analog transducer • convert I/p quantity into an analog o/p • Analog o/p- a continuous fn. Of time • Eg. Strain gauge, L VDT, thermocouple
Digital transducer • Converts I/p into an electrical o/p in the form of pulses
Inverse transducer • Which converts electrical signal to physical • quantity
Transducer for pressure measurement • What is pressure? force/ unit area Unit – (N/sq.m) Pa Pressure measured can be absolute , gauge or differential depending on type of reference
Types of pressure transducers • Gravitational eg : manometer • Elastic – force converted to strain eg. Diaphragm, capsule, bellows, bourdon tubes
Diaphragm Common pressure sensing elastic element Thin circular plate stretched & fastened at its periphery Made of elastic alloys of bronze,phosphor bronze, stainless steel or alloys like Monel, Nickel span -C
Flat type – high natural frequency • Corrugated – for large deflections
Capsule • Two corrugated metal diaphragms sealed together at periphery • Forms a shell like structure • One diaphragm has a port at centre to admit pressure to be measured • Other 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 section • Sealed at one end • Tends to straighten when pressure applied. • Angular sensitivity proportional to pressure applied
Helical type • Tube in the form of helix
Bourdon tube • More sensitive to shock & vibrations • Good repeatability
Bellows • Thin walled cylindrical sheets with deep convolutions sealed at one end • Sealed end moves axially when pressure is applied • No. of convolution s – vary from- 2 to 50 – depends on range, operating temp • Used for low pressure measurement
Bellows displacement y = 2.n. A q P Rx2 /( Et2 .) where n – no. of convolutions A q- effective area Et - young’s modulus of elasticity Rx – radius of diaphragm P – pressure ie, Y P
Resistive type Eg. Strain gauge
Inductive type • Eg. LVDT
Measurement of velocity Velocity – linear or angular
Linear velocity • Electromagnetic transducers • O/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 coil • Moving magnetic
Angular velocity • Tachometer - types Mechanical Electrical MHD sensor – magneto hydrodynamic sensor highly sensitive High precision
Transducer for vibration • Vibrations give early warning of impending conditions which may develop &vlead to complete failure & destruction of equipment • Used in power plants, turbines
Most vibrations are sinusodial in nature • Got amp & freq. • Amp gives displacement • By measuring displacement, velocity or acceleration - vibrations measured
Vibration transducer Accelometer – measures shock or vibration Pot type or LVDT type
