Expert’s answer: Type J thermocouple temperature variation
Many factors can cause a type J thermocouple temperature variation in your system. I’ll list steps to isolate the problem and give you a recommendation for a fix.
Good to hear you’ve already verified each junction box and found that the problem begins at the third box. Make sure the cable between the second and third box is for type J and also test the cable between the third box and the DCS.
If the cables check out fine, inspect the connections. An inversion on a cable connection can create an error in the temperature measurement. If you have a double inversion, the distributed control system (DCS) can read less than the real temperature and the value can be around 15 degrees Celsius.
You should also review the setup on the DCS for this type of thermocouple. Simulating millivolts direct to the DCS input will confirm if you have a problem there.
I recommend a wireless device to avoid this kind of problem and get your updates in seconds. You’ll clear up wrong measurements that happen because of incorrect installations.
If you want further information about temperature transmitters, check the links below:
Here you can learn more about wireless solutions:
Other resources that might interest you
Millivoltage for Type K thermocouple?
How do you find the millivoltage for the temperature in a type K thermocouple sensor?
RTD or thermistor or thermocouple?
Need a device that can handle regular temperatures between 1100 and 1200 degrees Celsius with excursions up to 1300 or 1400? In that case, which device is best – RTD or thermistor or thermocouple?