Problems with thermocouple installation

It’s 1000 degrees, so a K-type thermocouple can be used for measurement. As for whether heating is required or not, it depends on the actual conditions on site; if the environment is unfavorable, I don’t recommend using a thermocouple with temperature sensing capabilities. Compensating wires should be used with thermocouples, not ordinary twisted pairs. As for errors… Anyway, it’s definitely not allowed, right!

Here, the heating is adjusted on-site (the environment is good now), making maintenance convenient. It is said that without a compensation wire, the error is quite large.

There is a fluidized bed boiler equipped with a total of 20 thermocouples, operating at around 1000 degrees. What type of thermocouple would be suitable? Should K-type thermocouples be used, which are cost-effective; or should they be connected to the DCS cabinet using compensation wires and specialized thermocouple connectors? Alternatively, could a temperature conversion module be used on-site to convert the signal to 4–20 mA, after which it can be transmitted to the cabinet using ordinary wires? Generally, compensation wires are used to send the signals to the control room, and temperature conversion modules can also be used; however, in harsh field conditions, temperature conversion modules may not function properly. Which method is better in such situations? Can the thermocouple be connected to the cabinet using ordinary wires, without the need for compensation wires? If the temperature at the site remains constant, it is possible to make corrections manually without using a compensation wire, but this is practically not feasible. If a compensation wire is used, what will be the error level? The error lies in the temperature difference between the field terminal blocks and those in the control room

Thank you very much to all of you. What does a harsh environment mean? How severe is it? Could you describe it in detail? Such as wind, dust, thunder, rain, etc

K-type! It is necessary to heat it on-site to 4–20, after which ordinary wires can be used. Accuracy can be guaranteed

This post was last edited by Taohualing Jushi on 2016-1-5 at 16:26. The error is due to the temperature difference between the wiring terminals at the site and those in the control room. This error is variable; are there any good ways to compensate for it?

When using a K-type thermocouple, a compensation wire is necessary. Once, without using the compensation wire, I checked and found that the deviation was around 30 degrees.

K-type thermocouple with sleeve. The temperature at the site is 1000 degrees, making it unsuitable to use an integrated temperature sensor. If a temperature sensor is to be used, a separate one should be employed, with the data being transmitted to the DCS via ordinary cables; otherwise, compensation wires should be used, and the wire gauge should be increased by one size if the distance is too long.

Therefore, a compensation wire must be used to extend the thermocouple to the instrument’s terminal block; the temperature value measured at this terminal block is then used by the instrument to perform temperature compensation, thereby ensuring accurate measurements.

Normally, I connect the compensation wires directly to the thermocouple modules of the PLC or DCS. What is the difference between this approach and converting the signal into a current signal on-site before sending it back to the DCS?