Thermocouple problem
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It is a 3-wire thermocouple; one of the wires was measuring an out-of-range value. After removing the wiring and shorting the compensation wire, the control unit displayed the ambient temperature. When the thermocouple potential was measured, it was around 10 millivolts, the same as for the other two wires. After reconnecting the wiring, the control unit indicated an out-of-range value again. By disconnecting the compensation wire on-site, a potential of over 200 millivolts was measured. What could be the reason? Note: It is suspected that a fault exists in the card holder in the cabinet; after swapping the locations of the card holder and another 2-wire thermocouple pair, the fault persisted. Some expert, please give some advice!
“After shorting the compensation wire, the control panel shows the ambient temperature, which indicates that there are no issues with the wiring or connectors; the problem lies with the thermocouple. Try replacing it with another one.
I’ve never seen a three-core thermocouple, nor have I seen a three-core compensation wire. . . Is it really there?
Are there any photos? Post it so we can all learn together*.
The three-core thermocouple here is simply 3 thermocouples embedded inside a sleeve; generally, they have different lengths, allowing for the measurement of temperatures at various points. It’s quite common; it’s strange that so many people make such a fuss over it. :Lol, in this case, it’s most likely that the sensor chip has gone out of range and is damaged.
“Out of range---tens of millivolts---Out of range---over 200 millivolts”. It seems the lifespan of this thermocouple is coming to an end; time to replace it with a replacement.
Thermocouples are generally used in conjunction with temperature changes! Then, inside the access card module – I’m not sure if yours has one – if it does, check whether the temperature-related output is normal! Another simple method is to remove what you think is the problem and connect it to a normal one to see if the temperature reading is normal! After that, you’ll know where the problem lies!
If it works properly after replacing the thermocouple with one of the same type, does that mean the compensation wire is causing interference?
The voltage difference across the compensation wire at the connections between cabinets and at the field terminals is over 20 mV. After discharging, it was connected to the thermocouple temperature measurement circuit; the reading was normal at first, but in less than 5 minutes the reading exceeded the scale limits again. The grounding resistance was measured with a megohmmeter and turned out to be fine. Is it necessary to replace the compensation wire?