11 - displacement measurement

7/24/2019 11 - Displacement Measurement

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DisplacementDisplacement

MeasurementMeasurement


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With Many Applications in ControlTechnoloy! "nformation #eardin$isplacement and %enth has to &e$etected and Transmitted'

This "nformation can &e (&tained &yMeans of)

"ncremental Measurin System

A&solute Measurin System


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The $istance &et*een T*o Places can &e$etermined *ith the +elp of a Map and a

Pair of $i,iders &y Measurin Accordin toScale! a Specic $istance *ith the $i,idersand .sta&lishin +o* Many Times this"ncrement oes into the $istance &et*eenPlace A and Place /'

The %enth of the "ncrement Multiplied &ythe 0um&er of Steps i,es the $istance'

This System (nly Pro,ides "nteral Multiplesof the /asic nit'


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"f a Scale is sed "nstead of $i,iders! thenthe $istance can &e #ead $irectly and 0oCountin is #e3uired'

This is 4no*n as an A&solute Measurin

System &ecause the Measured aria&le can&e #ead $irect'


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The Simplest Form of Analoue Position

Sensin is the A&solute Measurement of a$istance Tra,elled &y Means of aPotentiometer'

The Function of a %inear Potentiometer is

/ased on the oltae $i,ider Principle!*here&y the $istance Tra,elled is

Transmitted to a Potentiometer! from *hichthe Position $ata can &e Accessed in theForm of an .lectrical oltae'


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The Potentiometer has a %inear #elationship

&et*een Shaft Position and Sinal (utput'

A

C

B

Resistance Element

Wiper Contact

Slide Bar

Input Shaft

Motion


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Wiper Position Signal Output

At the Centre +alf Applied oltae at (utput

At .6treme %eft 7ero oltae at (utput

At .6treme #iht Full oltae at (utput

The Same Principle Applies to the Anular$isplacement Potentiometer &ut in Terms ofaryin Anle of $isplacement'


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The %inear Potentiometer is Constructed in

the Form of a #odless Slidin Potentiometer*ith "n-%ine Couplin *hich is +oused in anAluminium Prole +ousin'

The Slidin Potentiometer is sed to Tap a

oltae *hich is Proportional to theConnected Supply oltae and the WiperPosition'


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The Same Principle Applies to the Anular

$isplacement Potentiometer &ut in Terms ofaryin Anle of $isplacement'

Input shaft Resistanceelement


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A $i9erent $isplacement Pro&e is the Piston

#od $isplacement Sensor'

"t is Widely sed in Mechanical .nineerinand Car Manufacturin! as Well as in#o&otics and Automation'

"ts $istinuishin Feature is it has reat#o&ustness and +ih Accuracy'


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Compared to Potentiometers! %$Ts has

+iher Accuracy and #elia&ility' Consists of

1 Primary Coil - .6cited &y AC Source 2 Secondary Coil - "nduced oltae

$epends on Core Position 1 Mo,a&le Core


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Secondarycoil 1

Primarycoil

Secondarycoil 2

CoreMotion

Inputshaft

Insulatingform

ExcitationSource

Dierenceoltageoutput

!"1 # "2$


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Core position

A

B

!

-

"oltage out%opposite phase

"oltage out

Core displacement

Core at & Core at '!null position$

Core at (


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The %inear $isplacement Capacitor Wor:s*ith Capacitance

Capacitance is $irectly #elated to Plate Areaand "n,ersely #elated to the Plate Spacin'

As the Metal Tu&e Mo,es to the #iht!

$istance &et*een Plates $ecrease andTherefore Capacitance "ncreases'


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Motion

Moing metal tu)e

Dielectric

*ixed metal tu)e


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Capacitance *ill "ncrease as the Mo,in

Plate Co,ers More of the Fi6ed Plate'

Moing Plate

*ixed plate


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11 - displacement measurement

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