Why Am I Getting Temperature Drift on My Thermocouples When My Cold Junction Temperature Changes?Primary Software: Driver Software>>NI-DAQmxPrimary Software Version: 7.4 Primary Software Fixed Version: 7.4 Secondary Software: N/A Hardware: SCXI>>Terminal Blocks>>SCXI-1328, SCXI>>Terminal Blocks>>SCXI-1300
Problem: I am using a terminal block to connect my thermocouples to my data acquisition or signal conditioning device, but I notice that when the temperature of the cold junction (CJ) changes that my measurements drift. Solution: This behavior can occur if a terminal block is being heated or cooled. What occurs in this situation is the temperature of the CJ sensor and the temperature of the CJ are actually at slightly different levels. The Data Acquisition (DAQ) calls for doing CJ compensation base the compensation measurements on the temperature of the CJ sensor. In some cases where there is rapid heating or cooling of the terminal base the temperature read by the built in compensator is at a different temperature than the temperature of the connections. Therefore when the compensation is done it does compensate for what the measured CJ temperature is. Since the actual CJ temperature is different than the measured CJ temperature measured by the CJ sensor then the measurements will be off by some amount and give the apparent drift. Workaround Make certain that the terminal base heats and cools in a consistent manner. Pay particular attention to see that nothing is heating one part of the connector more than any other. Related Links: Information on Cold Junction Compensation (CJC) Sensors Attachments:
Report Date: 03/21/2005 Last Updated: 04/08/2005 Document ID: 3JKEJ546 |
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