Design of Cold-Junction Compensation and Disconnection Detection Circuits of Various Thermocouples and Implementation of Multi-Channel Interfaces Using Them — A Secondary Publication

Abstract

Cold-junction compensation (CJC) and disconnection detection circuit design of various thermocouples (TC) and multi-channel TC interface circuits were designed. The CJC and disconnection detection circuit consists of a CJC semiconductor device, an instrumentation amplifier (IA), two resistors, and a diode for disconnection detection. Based on the basic circuit, a multi-channel interface circuit was also implemented. The CJC was implemented using compensation semiconductor and IA, and disconnection detection was detected by using two resistors and a diode so that IA input voltage became -0.42 V. As a result of the experiment using R-type TC, the error of the designed circuit was reduced from 0.14 mV to 3 µV after CJC in the temperature range of 0°C to 1400°C. In addition, it was confirmed that the output voltage of IA was saturated from 88 mV to -14.2 V when TC was disconnected from normal. The output voltage of the designed circuit was 0 V to 10 V in the temperature range of 0°C to 1400°C. The results of the 4-channel interface experiment using R-type TC were almost identical to the CJC and disconnection detection results for each channel. The implemented multichannel interface has a feature that can be applied equally to E, J, K, T, R, and S-type TCs by changing the terminals of CJC semiconductor devices and adjusting the IA gain.