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DISPLACEMENT TRANSDUCERS- OSCILLATION TRANSDUCER, PIEZO ELECTRIC TRANSDUCER, POTENTIOMETRIC TRANSDUCER & VELOCITY TRANSDUCERPrepared by,ASHA.S.SPHYSICAL SCIENCES.N.T.C

TRANSDUCER TRANSDUCER

It is a device which convert non electrical quantity In to an electrical signal

A transducer is a device which when calculated by energy in one transmission system, supplies energy in the same form or in another form to a second transmission system. This energy transmission may be electrical ,mechanical optical or thermal

DISPLACEMENT TRANSDUCERS

The conversion of applied force in to displacement is basic to many type of transducers.The mechanical element that convert the applied force summing devices.General force summing members are : 1. Diaphragm, flat or corrugated 2. Bellows 3.Bourdon tube ,circular or twisted 4. Straight tube 5. Mass cantilever , single or double suspension 6. Pivot torque

Pressure transducers generally use one of the first four types of force summing members (5)and (6) are found in accelerometer and vibration pick

Displacement created by the action of force summing device is converted in to change some electrical parameter.

The electrical principles most commonly used in the measurement of displacement are a) Capacitive b)Inductive c) Differential transformer d) Ionization e) Oscillation f)Photo electric g)Piezo electric h)Potentiometric i)Velocity

OSCILLATION TRANDUCER

This transducer uses the force summing member to change the capacitance or inductance in an LC oscillator circuitIt shows the basic elements of an LC oscillator whose frequency is affected by a change in the inductance of the coilStability of the oscillator must be excellent in order to detect changes in oscillator frequency caused by the externally applied force

It measures both statics and dynamic phenomena and in telemetry application.Its limited temperature range , poor thermal stability , and low accuracy restrict its use to low accuracy applications

Piezoelectric Transducer Asymmetrical crystalline materials , such as quartz, Rochelle salt , and barium titanite , produce an emf when they placed under stress.This property is used in piezoelectric transducers.Here the crystal is placed between a solid base and the force-summing member

An externally applied force entering the transducer through its pressure port, applies pressure to the top of a crystal. This produce on any of across the crystal, proportional to the magnitude of applied pressure.

Since the transducer has very good high frequency accelero meters .Here the output voltage is on the order of 1 to 30 MV per g of acceleration.The device need no external power source and so it is self generating.

Dis advantage is that it cannot measure static conditions .The output voltage is also affected by temperature variations of the crystal.

It is an electromechanical device containing a resistance element contacted by a movable sliderMotion of the slider results in a resistance change that may be linear, logarithmic,exponential and so on depending on the manner in which the resistance wire is wound.Deposited carbon, platinum film,and other techniques are used to provide resistance element

Potentiometric transducers

It is widely used ,Its electrical efficiency is very high and provide sufficient output to permit control operations without further amplifications.

The device may be AC or DC excited and operations can therefore serve a wide range of functions.

Because of the mechanical friction of the slider against the resistance element ,its life is limited and noise may develop as the element wears out.

Large displacements are usually required to move the slider along the entire working surface of the potentiometer.

VELOCITY TRANSDUCER

It essentially consists of a moving coil suspended in the magnetic field of a permanent magnet.

Voltage is generated by the motion of the coil in the field .

The output is proportional to the velocity of the coil and this type of pickup is therefore generally used for the measurement of velocities developed in a linear, sinusoidal or random manner.

Damping is obtained electrically ,there assuring high stability under varying temperature conditions.REFERENCEModern Electronic Instrumentation and Measurement Techniques: Albert D. Helfrick William D. CooperTHANK YOU