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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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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&