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.Based on principle of transduction 2.Active & passive 3.Analog & digital 4.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

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

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 R x 2 /( E t 2.) where n – no. of convolutions A q- effective area E t - young’s modulus of elasticity R x – 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 / R 2. dR/dt where N I / R 2 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

THANK U