Presenter:

Ibrar Khalid

2011-Ch-55

Department of Chemical Engineering

UET Lahore

Contents

IntroductionIntroduction• Displacement, a vector quantity• Represents change in position of a point or body

w.r.t reference point• Difference between coordinates of two points

• Used for the measurement of many derived quantities such as force , stress , pressure, velocity and acceleration etc.

• Force, pressure, velocity etc. in terms of displacement

NEEDS OF MEASUREMENT

IN THE MEASUREMENT OF PRESSURE

FOR EXAMPLE

Pressure

BourdonTube

DisplacementDisplacementTransducer

ElectricalSignal

1. Linear DisplacementLinear motion measured in few microns to few centimetres

2. Angular DisplacementRotational motion measured from a few seconds to 360o

TYPES OF DISPLACEMENT

For designing and selecting a displacement sensor we must know the following questions:

What is type of the displacement ? What resolution and accuracy is required ? What is required detection range ?What is the power dissipation ? What is the Cost of the conditioning circuit ?

SELECTION CRITERIA

DISPLACEMENT TRANSDUCER

DisplacementElectrical

SignalDisplacementTransducer

Displacement TransducerDisplacement Transducer• Converts physical quantity into electrical quantity• Two main parts

1. Sensing element or primary transducer

2. Transduction element or secondary transducer

SensingElement

Electrical

Signal

Electrical

Signal

TransductionElement

TransductionElement

Contact Type1. Variable resistance

Potentiometer2. Variable inductance

LVDT (Linear variable differential transformer) RVDT (Rotary variable differential transformer)

3. Variable capacitance Non Contact Type

1. Ultrasonic 2. IR Sensor

TYPES OF DISPLACEMENT TRANSDUCER

RESISTIVE TRANSDUCERSRESISTIVE TRANSDUCERS

CAPACITIVE TRANSDUCERSCAPACITIVE TRANSDUCERS

(0,0) Displacement

Capacitance,C

Change in capacitance is proportional to displacement

INDUCTIVE TRANSDUCERSINDUCTIVE TRANSDUCERS

Comparison of TransducersRESISTIVE Capacitive Inductive

Measure up to 100mm.for Linear

High Sensitivity High linearity

Measure 10O TO 3570. for Angular

Good frequency response High resolution

Loading effect

Stray capacitance effect Interference due to stray magnetic field

Minimum electric equipment required

Temperature sensitive Temperature insensitive

Economical Dust particle may cause change in capacitance

Non-contact type

It is not the end,

It is not even the beginning of end,

But it is end of beginning…..