MI 362Measurement and Instrument24/2/2014Lecture 19Principle of TransductionUsually quantity to be measured converted into electrical quantitySensor TechnologiesEnergy ConversionResistive transducersCurrent transducersEnergy ConversionPhotovoltaic Cell: incident light into electric energylight falls on unction bet!een dissimilar materials create a "otential di#erence bet!een the materials$ "otential di#erence is function of incident %u&$ o"en circuit voltage saturates at lo! intensities'hile( short)circuit current !or* linearly over large ranges of incident light$ Silicon based devices: "rovide large amounts of current used as "o!er source+as large ca"acitance: slo! res"onseEnergy ConversionThermocou"le: converts thermal energy into electrical energy$ voltage di#erence bet!een t!o !ires "ro"ortional to the tem"erature at the unction)Seebec* e#ect di#erent metal combinations have di#erent voltage di#erence$Energy ConversionElectromagnetic:conductor is moved in a magnetic ,eld-oltage induced in conductor "ro"ortional to rate at !hich conductor moves electrical generator( louds"ea*erEnergy Conversion+all E#ect:current carrying conductor "laced in a magnetic ,eld$ voltage develo"s "er"endicular to the direction of current and magnetic ,eld$ out"ut signal is a function of magnetic ,eld densityautomotive systems: angular "osition of cran* shaft for ,ring angle of the s"ar* "lugs( "osition of car seats and seat belts( air)bag control( !heel s"eed detection for anti)loc* bra*ing system(MI 362Measurement and Instrument24/2/2014Lecture 20ResistiveChange in the resistance of a device as some "hysical "arameter is changed: R./012Strain gauge( thermistor( "hotoconductive transducerthermistor and "hotoconductive transducer rely on changing concentration of charge carriersResistiveThermistor: based on semiconductors concentration of charge carriers changes !ith change in tem"erature ra"id decrease in resistivity as tem"erature increasesE&cellent for highly sensitive tem"erature measurements 3do!n to 4*)56)7 8$useful in the range of )566 6C through to 9:66 ;CResistivePhoto)conductive: or "hotoresistors 0ight of right !avelength can change the carrier concentration in a semiconductor by a large factorincident light must have enough energy to "romote the electrons across the band)ga" of the material$ Strain