Me kana Wani Mai Yadda Karamin Sali?
Misali mai Tsirrai na Tsafta?
Bayanin Misali mai Tsirrai na Tsafta
Misali mai Tsirrai na Tsafta (ko kuma Misali mai Tsirrai ko RTD) shine kayayyakin da ake amfani da su don tabbatar da tsafta ta hanyar bincike tsirrai na zane. Wannan zane suna ake kira misalin tsafta. Idan muna tabbatar da tsafta da kyau, RTD shi ne aikin da ya fi dace, saboda akwai tsari mai yawa har zuwa wurin tsafto. Wasu kayayyaki masu amfani a kan bincike tsafta sun hada da thermocouple ko kuma thermistor.
Yawan tsirrai na kayan kwalba a gaba da yawan tsafta an bayyana a cikin,
Amsa, Rt da R0 suna tsirrai a tsaftunan toC da t0oC. α da β suna abubuwan da suka dogara da kayan kwalba. Wannan bayani shine har zuwa wurin tsafto. Don wurin tsafto mai yawa, wannan bayani zai iya zama,A cikin
Kayayyakin RTD suna amfani da kayan kwalba kamar Copper, Nickel, da Platinum. Kila kayan kwalba suna da yawan tsirrai mai yawa wanda ya dogara da yawan tsafta, wanda ake kira tsirrai-tsafta.
Platinum yana da wurin tsafta 650oC, sannan Copper da Nickel suna da 120oC da 300oC tasashe. Fig-1 ya nuna tsirrai-tsafta curve na uku kayan kwalba. Don Platinum, tsirrai yake yana canzawa kimanin 0.4 ohms kafin tsafta ya canza baya daya Celsius.
Zafi na Platinum a cikin RTDs an tabbata da ratio R100 / R0. Abubuwa a cikin abinci suna haɗa da fuskantar tsirrai-tsafta, wanda ke haɗa da α da β values na kayan kwalba.
Gargajiya Misali mai Tsirrai na Tsafta ko RTD
Gargajiya shine kadan a cikin hanyar da ake rube zane a form (a coil) a cikin mica cross frame don samun yanayin kadan, don samun thermal conductivity don kawo wakar takam, da kuma samun kungiyar kula mai yawa. A cikin RTD na gabashin, coil yana da take da sheath na stainless steel ko kuma protective tube.
Saboda haka, strain na fiziki yana da yawa saboda zane yana ciwo da karamin tsafta. Idan strain a cikin zane yana ciwo, maka tension yana ciwo. Saboda haka, tsirrai na zane zai canzawa wanda ba a duba. Saboda haka, ba muna son canza tsirrai na zane da wasu abubuwan da ba suka dole wa tsafta.
Wannan yana taimaka wajen babban girma na RTD idan plant yana yi aiki. Mica an koye a cikin steel sheath da resistance wire don samun electrical insulation. Saboda yawan strain a cikin resistance wire, yana bukatar da ake rube da damar daidai a mica sheet. Fig.2 ya nuna structural view na Industrial Resistance Temperature Detector.
Signal Conditioning na RTD
Muna iya samun RTD a kasuwa. Amma muna bukata a taimaka game da hanyar ake amfani da shi da kuma hanyar ake gina signal conditioning circuitry. Saboda haka, errors na lead wire da wasu calibration errors za a iya kudan. A cikin RTD, yawan tsirrai value yana da yawa kimanin tsafta.
Tsirrai na RTD an tabbata ta hanyar bridge circuit, inda ake bayar electric current daidai kuma ake bincike voltage drop across a resistor don kula tsafta. Tsafta shine an tabbatar da convert RTD resistance value using a calibration expression. Modules of RTD suna nufin a cikin figures.
A cikin two wires RTD Bridge, dummy wire ba a cikin ba. Output an tabbatar da shi daga labaran ends kamar yadda aka nuna a fig.3. Amma extension wire resistances suna da muhimmanci don in duba, saboda impedance na extension wires zai iya haɗa da tsafta reading. Wannan effect an kudan a three wires RTD bridge circuit by connecting a dummy wire C.
A cikin three-wire RTD, idan wires A da B suna da yarda da karamin area, impedaansa effects suna haɗa da shi. Dummy wire C yana da shi a matsayin sensing lead don bincike voltage drop without carrying current. A cikin circuits, output voltage yana da tsari mai yawa da tsafta. Saboda haka, muna bukata calibration equation don tabbatar da tsafta.
Expressions for a Three Wires RTD Circuit
Idan muna sanin VS da VO, muna iya tabbatar da Rg kuma muna iya tabbatar da tsafta value using calibration equation. Za a iya kula, assume R1 = R2:
Idan R3 = Rg; then VO = 0 and the bridge is balanced. Wannan zai iya a yi manually, amma idan ba muna son yi manual calculation, muna iya kula solve the equation 3 don get the expression for Rg.
Wannan expression assumes, when the lead resistance RL = 0. Suppose, if RL is present in a situation, then the expression of Rg becomes,
Saboda haka, akwai error a cikin RTD resistance value because of the RL resistance. Saboda haka muna bukata a compensated the RL resistance as we discussed already by connecting one dummy line ‘C’ as shown in fig.4.
Limitations of RTD
A cikin RTD resistance, akwai I2R power dissipation by the device itself that causes a slight heating effect. This is called as self-heating in RTD. This may also cause an erroneous reading. Thus, the electric current through the RTD resistance must be kept sufficiently low and constant to avoid self-heating.
