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Measurements and SensorsThird Year 

Mechatronics Department

Al-Khawarizmi College of EngineeringUniversity of aghdad

!"#$ - !"#%

Dr& '(rat )*rahim +(ssein Al-,aar 

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.eferences/#0 )nstr(mentation1 Meas(rements and Analysis& C ,a2ra and K K Cha(dhry1

!3nd edition& Tata Mc4raw-+ill 5(*lishing1 !""$&

!0 6ensors for Mechatronics& 5a(l 5&7& .egtien1 #3st edition& Elsevier )nc1 !"#!&

80 E9perimental Methods for Engineers& :& 5& +olman1 eighth edition& Mc4raw-+ill

5(*lishing1 !"#!&

The aim of the two co(rses/; Define the *asic concepts of instr(mentation1

; .eview the sensors characteristics1

; 6t(dy some sensors techni<(es1; 6t(dy some act(ators techni<(es1 and

; '(ndamentals of essential meas(rements processes&

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Chapter OneInstruments and their Representation

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Meas(rement: A method to o*tain information

regarding a physical val(es of the varia*le&

)nstr(mentation:  Devices and applications (sed in

meas(rement system

Instrumentation and measurements is the field that

encompasses areas of detection1 ac<(isition1 control and

analysis of data in almost all the areas of science and

technology& 

Instruments and their Representation

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MeasurementSystem

  m  e  a

  s  u  r  e  d

 S e n s

 o r,  s  i g n

 a  l  c o

 n d  i  t  i o

 n  i n g,  d  i s p  l a y

  M  a  n

 ,   t  r  a

  c   k   i  n

  g   c  o  n

  t  r  o   l   e

  t  c

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Instrumentation applications covers three major areas:

#0 Meas(ring physical <(antities s(ch as length1 vol(me

temperat(re and mass in terms of standard (nits&

Simple instrument model for

measuring physical quantities

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7/23/2019 Measurements and Sensors - CH1 Introduction

http://slidepdf.com/reader/full/measurements-and-sensors-ch1-introduction 8/30Temperat(re meas(ring in a simple water heating process

!0 Monitoring f(nctions and providing necessary information

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80 A(tomatic controlling of systems thro(gh (sing a part of

a(tomatic feed*ac2 to control systems&

Temperat(re and flow =or level0 control in a water heating (nit&

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4eneralised meas(ring system

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Measuring System Stages

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Calibration/ is the act or res(lt of <(antitative

comparison *etween a 2nown standard and the

o(tp(t of the meas(ring system meas(ring for

the same type <(antity&

)n a way1 the process of cali*ration is in effect

the proced(re for determining the scale of themeas(ring system&

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• 5hysical <(antity/ varia*le s(ch as press(re1 temperat(re1 mass1 height1

distance1 speed1 etc&

• Data/ )nformation o*tained from the instr(mentation>meas(rementsystem as a res(lt of the meas(rements made of the physical <(antities

• )nformation/ Data that has a cali*rated n(meric relationship to the

 physical <(antity&

• 5arameter / 5hysical <(antity within defined =n(meric0 limits&• Transd(cer  is an electrical device that converts one form of energy into

another&

• A transd(cer with a non-electrical inp(t is an inp(t transd(cer 1

intended to convert a non-electrical <(antity into an electrical signal inorder to meas(re that <(antity&

• A transd(cer with a non-electrical o(tp(t is called an o(tp(t transd(cer 1

intended to convert an electrical signal into a non-electrical <(antity in

order to control that <(antity&

Definitions

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Accordingly1 these transd(cers are also called sensor  and

actuator1 respectively

Sensor is an inp(t transd(cer and

 an Actuator is an o(tp(t transd(cer&

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Act(ators

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'(nctional elements of a meas(rement system

#0 asic f(nctional elements !0 A(9iliary f(nctional elements

Transd(cer 

6ignal conditioning element

6ignal Transmission

Data presentation element

Cali*ration element

E9ternal power element

'eed*ac2 element

Microprocessor element

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Typical e9amples of transd(cer elements

Some !"amples of Identification of

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#0 Transd(cer element/ the t(*e acts as a transd(cer element as it

converts the inp(t fl(id press(re into a displacement at its free end&

!0 6ignal conditioning elements/ the displacement is amplified *y thecom*ined lever and the gearing assem*ly&

80 Data presentation/ the movement of the pointer attached to the gear

on a scale gives an indication of the press(re&

Mechanical ourdon tube pressure gaugeSome !"amples of Identification of

#unctional !lements in Instruments

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Digital o(rdon press(re ga(ge

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Electrodynamic displacement

meas(ring device

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Sensing and controlling the

temperature of a $ater reservoir

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)nstr(ments Classification

%& !nergy considerations

? 5assive instr(ments/ self-operated instr(ments that are the o(tp(t

energy =o(tp(t signal0 is s(pplied *y its inp(t signal&

6(ch as/ glass thermometer1 o(rdon t(*e press(re meas(ring device

e9pos(re meter of a camera1 which is in effect1 a photovoltaic cell1 5itot

t(*e for the meas(rement of fl(id flow velocity1 a tachogenerator for

meas(rement of rpm1 etc&

f

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 Airbus A'()* pitot tube +right&

Air-fow is right to let.tachogenerator for

measurement of rpm

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? Active instr(ments/ they are power-operated instr(ments that

re<(ire a(9iliary so(rce of power =s(ch as compressed air1 electricity1

hydra(lic s(pply1 etc0 for their operation&

6(ch as/ the differential transformer which is (sed in themeas(rement of displacement1 force1 press(re& etc& and float-type

 petrol tan2 level indicator&

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,& Analog and -igital .ypes

? Analog instr(ments  present the information in the form of

contin(o(s or stepless variations with respect to time&

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? Digital instr(ments  present the meas(red physical varia*les are

represented *y digital <(antities which are discrete and vary in steps&

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'& /peration on a deflection or null principles

? Deflection instr(ment/ is that in which the physical effect

generated *y the meas(ring <(antity prod(ces an e<(ivalent opposing

effect in some part of the instr(ment and this effect is closely relatedto some varia*le li2e mechanical displacement or deflection in the

instr(ment&

E9amples/ a typical spring *alance1 *o(rdon t(*e1 etc& The deflection

of the spring is however magnified *y an electrical device li2e 7@DTor *y (sing s(ita*le lever and gear mechanisms to *e read off from

the scale of the instr(ment&

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? ,(ll instr(ment/ a device that generates an e<(ivalent opposing

effect to n(llify the physical effect ca(sed *y the <(antity to *e

meas(red& The e<(ivalent n(ll-ca(sing effect in t(rn provides the

meas(re of the <(antity&E9amples for s(ch type are dead weight press(re ga(ge1 e<(al arm

 *alance and electrical resistance meas(rement *y heatstone *ridge&

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0& Contacting and 1on2Contacting .ypes

Contacting type of instr(ment is one that is 2ept in the meas(ring

medi(m itself s(ch as a clinical thermometer is an e9ample of s(chinstr(ments&

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 ,on-contacting or pro9imity instr(ments type meas(re the desired

inp(t even tho(gh they are not in close contact with the meas(ring

medi(m& 'or e9ample1 a varia*le rel(ctance tachometer1 which

meas(res the rpm of a rotating *ody1 is also a pro9imity type of

instr(ment& )n this1 the toothed rotor made of ferromagnetic material

ca(ses variation of fl(9 in the magnetic circ(it d(e to changes in air

gap& This in t(rn ind(ces an emf that is in the form of p(lses& The

o(tp(t of the instr(ment is fed to a fre<(ency co(nter from which the

rpm of the rotor can *e determined&