Thermocouple problem
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May I ask, when using a multimeter to measure a thermocouple, do you unscrew one of the two wires for measurement? Then, look up the corresponding temperature for the measured millivolt value – should the ambient temperature be added as well? Is the ambient temperature simply the temperature obtained by connecting the two wires together?
To measure the millivolt signal, there is no need to disconnect any wires; it can be measured directly
It can be measured using a multimeter; a temperature difference is required between the measuring terminal and the reference terminal
The last edit to this post was made by xxkhc on 2022-8-1 at 15:43. The correct approach is as follows: (there’s no need to disconnect the wires; just connect them and take measurements, ensuring good contact.) First, measure the thermoelectric potential UX of the thermocouple. Then, using the ambient temperature (i.e., the temperature of the reference terminal), refer to the thermocouple calibration table to find the thermoelectric potential U0 corresponding to that temperature. Add UX and U0 together to obtain the total thermoelectric potential, and then use the calibration table again to determine the actual temperature being measured.
When using a multimeter to measure a thermocouple, it is best to untwist one of the two wires for measurement. The measured data are in accordance with the law of the intermediate temperature of thermocouples: the electromotive force between the two junctions of a thermocouple circuit (at temperatures T and T0) is equal to the algebraic sum of the electromotive forces of the thermocouple at temperatures T and Tn, and at temperatures Tn and T0. Tn is referred to as the intermediate temperature. ) for processing ； When using a multimeter to measure a thermocouple, it is possible to conduct the measurement without unplugging the two wires; however, the result obtained in this case represents the value corresponding to two thermocouples connected in parallel (the hot ends of these two thermocouples are respectively the original hot end and the original cold end of the thermocouple, while the measurement point is at the common cold end of both thermocouples). This makes data processing more complicated, and it becomes even more difficult if there is an electronic compensation circuit for the original cold end. So it is not recommended to do this. .
The thermocouple millivolt signal is a low-voltage, high-impedance signal; if the multimeter’s impedance is not sufficient, significant errors will occur.