1- Sensor Fundamentals


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Sensors & Actuators
Department of Mechatronics Engineering
EEM304 Mechatronics
1- Sensor Fundamentals
Dr. Hassan SHARABATY
Sensors& Actuators -Sensor Fundamentals 2/14
Asensorisadevicethatconvertsaphysicalphenomenonintoanelectricalsignal.Assuch,sensorsrepresentpartoftheinterfacebetweenthephysicalworldandtheworldofelectricaldevices,suchascomputers.Theotherpartofthisinterfaceisrepresentedbyactuators,whichconvertelectricalsignalsintophysicalphenomena.
General architecture of a measurement system
Non-electrical signals
Non-electrical signals
Sensor
Sensor
Actuator
Actuator
Measurement system
Measurement System
AcquisitionProcessingDistribution
Data DataData
Dr. Hassan SHARABATY
Sensors& Actuators -Sensor Fundamentals 3/14
Sensor
Non-electrical signal
Electrical signal
Input transducer (sensor)
ES
N-ES
asensorisadevicethatreceivesasignalorstimulusandrespondswithanelectricalsignal,whileatransducerisaconverterofonetypeofenergyintoanother.
N-ES:suchastemperature,force,pressure,flow,position,lightintensity,humidity,…etc.
Transducers and sensors
Transfer Function
Dr. Hassan SHARABATY
Sensors& Actuators -Sensor Fundamentals
4/14
Sensors classification
Sensorsmaybeclassifiedinanumberofways.
Passive(orself-generating)sensorsgeneratetheirownelectricaloutputsignalwithoutrequiringexternalvoltagesorcurrents.Ex:thermocouplesandphotodiodeswhichgeneratethermoelectricvoltagesandphotocurrents,respectively,whichareindependentofexternalcircuits.
Active(ormodulating)sensorrequiresanexternalsourceofexcitation.
i.emostoftheoutputsignalpowercomesfromanauxiliarypowersource.Theinputonlycontrolstheoutput.
1-Inconsideringtheneedforapowersupply,sensorsareclassifiedas:
Resistor-basedsensors(thermistors,RTDs,andstraingages)areactivesensors,becauseacurrentmustbepassedthroughthemandthecorrespondingvoltagemeasuredinordertodeterminetheresistancevalue.
Dr. Hassan SHARABATY
Sensors& Actuators -Sensor Fundamentals
5/14
Sensors classification
1-Inconsideringtheneedforapowersupply,sensorsareclassifiedas:
PS.Itshouldbenotedthatthesedefinitions(active,passive)refertotheneed(orlackthereof)ofexternalactivecircuitrytoproducetheelectricaloutputsignalfromthesensor.Itwouldseemequallylogicaltoconsiderathermocoupletobeactiveinthesensethatitproducesanoutputvoltagewithnoexternalcircuitry.However,theconventionintheindustryistoclassifythesensorwithrespecttotheexternalcircuitrequirementasdefinedabove.
Sensorsmaybeclassifiedinanumberofways.
Dr. Hassan SHARABATY Sensors & Actuators – Sensor Fundamentals 6/14
Sensors classification
1- In considering the need for a power supply, sensors are classified as:
Sensors may be classified in a number of ways.
Dr. Hassan SHARABATY
Sensors& Actuators -Sensor Fundamentals
7/14
Sensors classification
2-Inconsideringoutputsignals,weclassifysensorsasanalogordigital.
Analogsensorshaveanoutputthatiscontinuousoverafiniteregionofinputs.
Ex:potentiometers,LVDTs(linearvariabledifferentialtransformers),loadcells.
Theoutputofdigitalsensorstakestheformofdiscretestepsorstates.DigitalsensorsdonotrequireanADC,andtheiroutputiseasiertotransmitthanthatofanalogsensors.Digitaloutputisalsomorerepeatableandreliableandoftenmoreaccurate.Ex:Positionencoder.
Sensorswhoseoutputisavariablefrequencyarecalledquasi-digitalbecauseitisveryeasytoobtainadigitaloutputfromthem(bycountingforatime).
-But regrettably, digital sensors cannot measure many physical quantities.
Sensorsmaybeclassifiedinanumberofways.
Dr. Hassan SHARABATY
Sensors& Actuators -Sensor Fundamentals 8/14
Figure 1a Analogue sensor output
Figure 1b Digital sensor output
Sensors classification
2-Inconsideringoutputsignals,weclassifysensorsasanalogordigital.
Ananalogsensoroutputconditionedbyananalog-to-digitalconverter(ADC)hasthesamedigitaloutputcharacteristics.
Sensorsmaybeclassifiedinanumberofways.
Dr. Hassan SHARABATY
Sensors& Actuators -Sensor Fundamentals
9/14
Sensors classification
3-Inconsideringtheinput-outputrelationship,sensorscanbeclassifiedaszero,first,second,orhigherorder.
Theorderisrelatedtothenumberofindependentenergy-storingelementspresentinthesensor,andthisaffectsitsaccuracyandspeed.Suchclassificationisimportantwhenthesensorispartofaclosed-loopcontrolsystembecauseexcessivedelaymayleadtooscillation.
Sensorsmaybeclassifiedinanumberofways.
Dr. Hassan SHARABATY
Sensors& Actuators -Sensor Fundamentals
10/14
Sensors classification
4-Inordertostudythesemyriaddevices,itiscustomarytoclassifythemaccordingtothemeasurand.
Thisclassification,however,canhardlybeexhaustivebecauseoftheseeminglyunlimitednumberofmeasurablequantities.Consider,forexample,thevarietyofpollutantsintheairorthenumberofdifferentproteinsinsidethehumanbodywhosedetectionisofinterest.
Consequentlywespeakofsensorsfortemperature,
Sensorsmaybeclassifiedinanumberofways.
pressure,
flow,
level,
humidity,
pH,
odor,
position,
velocity,
acceleration,
force, and so forth.
Dr. Hassan SHARABATY
Sensors& Actuators -Sensor Fundamentals
11/14
Sensors classification
5-Electronicengineersprefertoclassifysensorsaccordingtothevariable
electricalquantity
Thisapproachreducesthenumberofgroupsandenablesthedirectstudyoftheassociatedsignalconditioners.
Table 1
Sensorsmaybeclassifiedinanumberofways.
-Rresistance,capacity,inductance-andthentoaddsensorsgeneratingvoltage,charge,orcurrent,andothersensorsnotincludedintheprecedinggroups,mainlyp-njunctionsandradiation-basedsensors.
Dr. Hassan SHARABATY
Sensors& Actuators -Sensor Fundamentals 12/14
Sensorshavemanycharacteristicsthataffecttheirmeasurementcapabilitiesandtheirsuitabilityforeachapplication.
Sensor Characteristics:
some of the more
Transfer Function
Thetransferfunctionshowsthefunctionalrelationshipbetweenphysicalinputsignalandelectricaloutputsignal.Usually,thisrelationshipisrepresentedasagraphshowingtherelationshipbetweentheinputandoutputsignal.
ES
N-ES
Dr. Hassan SHARABATY
Sensors& Actuators -Sensor Fundamentals 13/14
END
Tobecontinued:
RestofSensorCharacteristics:
Range –Resolution –Sensitivity –Linearity -Accuracy …
Dr. Hassan SHARABATY
Sensors& Actuators -Sensor Fundamentals 14/14
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