How to check K-type thermocouples and Pt100 calibration tables

No, you also need to take into account cold-end compensation; the measured potential must be increased by the potential corresponding to the current temperature at the site, and the temperature corresponding to that potential needs to be determined.

The temperature obtained from the table must be added to the current ambient temperature to obtain the actual temperature of the medium.

For PT100, just use the corresponding resistance value; for thermocouples, the ambient temperature needs to be taken into account

The millivolt value is measured on-site using a thermocouple; the temperature obtained from a lookup table, plus the compensation temperature in the control room, gives the actual temperature； The thermal resistance value can be checked directly; in theory, both AB and AC values can be used. As a precaution, it’s advisable to check whether the AB and AC resistance values are equal; if they aren’t, there is a problem with the thermal resistor. I hope this helps

Normally, when dealing with temperature-related issues, I don’t use a dial gauge – I don’t even have one. Hehe, what should I do? I came up with a silly solution. The thermoelectric potential of a thermocouple is the potential difference between its hot end (the front end of the thermocouple element, i.e., the part that is inserted into the pipeline or device containing the medium to be measured) and its cold end. The millivolt potential measured with a multimeter reflects this temperature difference, which is the difference between the temperature of the medium and the temperature of the connection terminals (i.e., the ambient temperature). Therefore, by knowing the temperature at the terminal, it is possible to determine the temperature of the medium being measured. Normally, when dealing with faults, it is the process engineers who notice that there is a significant difference between the temperature at the point under inspection and the theoretical value expected based on operational parameters; only then do they ask the instrument technicians to carry out repairs. Therefore, when handling such situations, I use estimated values for the ambient temperature – I roughly assume that the temperature at the site is either 20 degrees, 25 degrees, or 30 degrees, and a difference of 4 or 5 degrees is not considered significant. Once the temperature at the terminal is known, the temperature of the medium being measured can be determined. Since there is no calibration table, and even if one were available it would not be convenient to use, I came up with a simple workaround: by checking the calibration table for K-type thermocouples, one can identify a general pattern. 10 degrees corresponds to a thermoelectrical potential of 0.4 mV; this is also an approximate value that can be used for troubleshooting. However, the accuracy of such measurements is relatively low. Therefore, at the site, after measuring the voltage in millivolts with a multimeter, one divides this value by 0.4 and then multiplies the result by 10 to obtain the temperature difference between the hot end and the connection terminals. By adding the estimated temperature at the site, the temperature of the medium being measured can be determined. As for PT100, it is much easier to work with: 0 degrees corresponds to 100 ohms, and there is a linear relationship between temperature and resistance. 3.9 ohms correspond to 10 degrees; therefore, by measuring the resistance value at the field wiring terminals, subtracting 100 ohms from it and then dividing by 3.9, one can determine the temperature at that point. However, 3.9 is not easy to calculate mentally, so it is often approximated as 4 ohms, which simplifies the process of troubleshooting in the field.

Thermocouple: The measured potential corresponds to the temperature + the temperature at the measurement point. Thermal resistor: The measured resistance corresponds to the temperature