E1C08 09/14/2010
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temperature measuring devices with built-in reference junction compensation, and many digital data
acquisition cards for personal computers include built-in reference junction compensation. The
electronics generally rely on a thermistor, a temperature-sensitive integrated circuit, or an RTD to
determine the reference junction temperature, as shown for a thermistor in Figure 8.18.
Potentiometer
Chromel
Ice bath
Chromel
Constantan
Measuring
junction
Reference
junction
(a)
(b)
Potentiometer
Copper
Copper
Ice bath
Chromel
Constantan
Measuring
junction
Reference
junction
Figure 8.17 Thermocouple temperature measurement circuits.
Thermistor
Output
Thermocouple
input
Figure 8.18 Basic thermistor circuit for thermocouple reference junction compensation.
8.5 Thermoelectric Temperature Measurement 335