The thermocouple circuit shown in Figure 2 represents the basis upon which thermocouple standard tables have been established. A new junction is added and held in an ice bath at Tice (0°C). The standards community and thermocouple manufacturers use this topology to develop tables of thermocouple voltage versus temperature.
Sa*(Tx-Tc) + Sc*(Tc-Tv) + VTC + Sc*(Tv-Tc) + Sa*(Tc-Tice) + Sb*(Tice-Tx) = 0 --Equation. 4
Rearranging and simplifying:
Sab*(Tx-Tice) = [VTC] --Equation. 5
(Values of Sa and Sb determine [VTC] polarity)
Modern signal conditioning modules use semiconductor electronics, which eliminate clumsy ice-baths by electronically simulating reference junction ice-point temperatures. This process is referred to as Cold-Junction-Compensation, CJC. In addition, these modern signal-conditioning modules linearize the non-linear behavior of Seebeck effect and provide linear scaled outputs in volts or amperes per degree.
Wed, 2010-09-01 15:37
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