Regarding the issue of built-in compensation in thermocouples
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The K-type thermocouples used in the new hydrogenation unit installed in our factory were not specified with any particular requirements during procurement; as a result, the manufacturer included its own compensation mechanism. When we introduced the DCS system, we applied additional compensation to those thermocouples. The problem now is that there are frequent errors in the temperature readings, and it has been determined that the issue lies with the built-in compensation mechanism. Does anyone have any ideas on how to resolve this problem? If compensation is disabled on the DCS side, what will happen if the built-in temperature compensation fails? Moreover, the hydrogenation pressure in our plant is quite high; in many locations, only remote temperature readings are available, with no on-site measurements. The ratio is roughly 800 to 900 for remote readings and 70 to 80 for on-site readings. Please think of a solution.
“\"The thermocouple has built-in compensation\" refers to temperature variation; compensation has already been applied, so there is no need to set automatic compensation in the DCS settings. Replace it if the temperature control fails.....
It’s not a temperature-related issue; it’s definitely a K-type thermocouple. The built-in compensation function also needs to be checked with the manufacturer
Compensation can be either internal within the DCS or external. I’m not sure what type of external compensation is used in your case; if it’s related to temperature, then an internal temperature-sensitive element could be used, but if not, then compensation wires would be necessary. You need to choose one of these two options. So there’s no need to worry too much about what will happen if the compensation mechanism fails. If that’s your only concern, then using DCS-based compensation is relatively more stable.
We didn’t know that the thermocouples had built-in compensation, so all temperatures were compensated using the DCS. Now the problem is that the compensation mechanism within the thermocouples malfunctions; as a result, the temperature readings are 10 to 20 degrees lower than the actual value. It’s difficult to detect this issue, and it seems challenging to resolve it.
Thermocouples do not compensate automatically; this must be done by a third party, such as a temperature module, or by using compensation wires in place of ordinary wires
Actually, I still haven’t understood it. The thermocouple has been compensated; how was it compensated? If the temperature changes, the DCS channels all change as well – how can this be compensated for? How can it self-compensate without temperature variation?
Does the thermocouple have built-in compensation? I’ve never heard of it; the manufacturer must be tricking you. Waiting for the expert to explain.
I don’t know. Anyway, problems keep occurring; the temperature at which these problems arise is about ten degrees lower than that at the same location. It’s quite troublesome now, and it’s hard to determine the cause. As for deception, that’s unlikely – it’s the boss’s colleague, with whom we’ve been working together for many years, and there have never been any issues
Items contacted in personal use: 1. Those that are connected to the system directly through a safety barrier without undergoing temperature changes; the safety barrier has temperature compensation, and the system configuration sets the temperature in the central control cabinet area to 25 degrees. 2. The manufacturer provides a dedicated thermocouple terminal box, which contains an 8-channel circuit board; once it is connected on-site, no further attention is required. 3. Convert the temperature signal to 4~20mA for input into the system. When I first started working, the more experienced workers mentioned that when thermocouples are calibrated at the factory, there are two options for the calibration temperature of the cold ends: 0 degrees and 25 degrees. It’s necessary to determine whether the thermocouple was calibrated at 0 degrees or 25 degrees when it’s used in practice; that’s roughly what they said. Over time, I can’t remember the details clearly anymore. Personal opinion, for reference only.