外文翻译(供热站温度实时监测).doc

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1、HeatingtemperatureandpressuretestThermistorsareinexpensive,easily-obtainabletemperaturesensors.Theyareeasytouseandadaptable.Circuitswiththermistorscanhavereasonableoutoutvoltages-notthemillivoltoutputsthermocoupleshave.Becauseofthesequalities,thermistorsarewidelyusedforsimplet

2、emperaturemeasurements.They'renotusedforhightemperatures,butinthetemperaturerangeswheretheyworktheyarewidelyused.Thermistorsaretemperaturesensitiveresistors.Allresistorsvarywithtemperature,butthermistorsareconstructedofsemiconductormaterialwitharesistivitythatisespeciallysensi

3、tivetotemperature.However,unlikemostotherresistivedevices,theresistanceofathermistordecreaseswithincreasingtemperature.That'sduetothepropertiesofthesemiconductormaterialthatthethermistorismadefrom.Forsome,thatmaybecounterintuitive,butitiscorrect.Hereisagraphofresistanceasafunc

4、tionoftemperatureforatypicalthermistor.Noticehowtheresistancedropsfrom100kW,toaverysmallvalueinarangearoundroomtemperature.Notonlyistheresistancechangeintheoppositedirectionfromwhatyouexpect,butthemagnitudeofthepercentageresistancechangeissubstantial.TemperatureSensor-TheTherm

5、ocoupleYouareat:Elements-Sensors-ThermocouplesReturntoTableofContentsAthermocoupleisajunctionformedfromtwodissimilarmetals.Actually,itisapairofjunctions.Oneatareferencetemperature(like0oC)andtheotherjunctionatthetemperaturetobemeasured.Atemperaturedifferencewillcauseavoltageto

6、bedevelopedthatistemperaturedependent.(ThatvoltageiscausedbysomethingcalledtheSeebeckeffect.)Thermocouplesarewidelyusedfortemperaturemeasurementbecausetheyareinexpensive,ruggedandreliable,andtheycanbeusedoverawidetemperaturerange.Inparticular,othertemperaturesensors(likethermi

7、storsandLM35sensors)areusefularoundroomtemperature,butthethermocouplecanTheThermocoupleWhyUsethermocouplesToMeasureTemperature?Theyareinexpensive.Theyareruggedandreliable.Theycanbeusedoverawidetemperaturerange.WhatDoesAThermocoupleLookLike?Hereitis.Notethetwowires(oftwodiffere

8、ntmetals)joinedinthejunction.Whatdoesathermocoupledo?Howdoesi