displacement measurement
TRANSCRIPT
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Presenter:
Ibrar Khalid
2011-Ch-55
Department of Chemical Engineering
UET Lahore
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Contents
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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
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• 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
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IN THE MEASUREMENT OF PRESSURE
FOR EXAMPLE
Pressure
BourdonTube
DisplacementDisplacementTransducer
ElectricalSignal
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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
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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
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DISPLACEMENT TRANSDUCER
DisplacementElectrical
SignalDisplacementTransducer
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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
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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
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RESISTIVE TRANSDUCERSRESISTIVE TRANSDUCERS
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CAPACITIVE TRANSDUCERSCAPACITIVE TRANSDUCERS
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(0,0) Displacement
Capacitance,C
Change in capacitance is proportional to displacement
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INDUCTIVE TRANSDUCERSINDUCTIVE TRANSDUCERS
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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
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It is not the end,
It is not even the beginning of end,
But it is end of beginning…..
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