Transcript Transducer
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 1. 2. 3. 4. 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 Structure – flat or corrugated Top view of flat type Top view of corrugated type • Flat type – high natural frequency • Corrugated – for large deflections Capsule 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 Spirial bourdon tubes Bourdon tubes –C type Helical type • Tube in the form of helix Bourdon tube • More sensitive to shock & vibrations • Good repeatability Bellows 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 Rx 2 /( Et 2 .) 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 Capacitive 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 Pot type accelrometer LVDT accelorometer M069.gif THANK U