DCS does not correspond to on-site thermocouple temperature values
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Today, we had another battle with the DCS maintenance staff. The thermocouple used in our on-site instrument maintenance is one thermocouple with two supplementary wires. The difference between control and measurement is about 2 degrees. The process control index is 506 degrees. The phenomenon is that the temperature controlled on site becomes between 499-502 by DCS, and changes and fluctuates frequently, which is unacceptable to the process. We used standard instruments 1045 and 1064 at the site to send signals to the control room respectively, and there was no problem. However, once connected to the DCS, it did not work. The resistance of our supplementary wires may be higher, but by replacing the card channel, the effect of impedance can be overcome. In the end, the problem has not been completely solved. The stable measurement is achieved by replacing the DCS control function block of measurement and control. I don't know if there is any complete solution. DCS is a simplified version of CS3000. For the first time, the safety barrier was basically collapsed.
We also encountered this problem, and the problem was completely solved after DCS replaced the safety barrier. It is probably related to the quality of the DCS safety barrier.
It is recommended to try using an isolation safety barrier for temperature signals, which can eliminate some interference on the lines!
You can also check whether the fastening screws of the thermocouple temperature are loose.
The third floor is right, don't use Zener safety barriers, or just don't use safety barriers at all.
We also encountered this problem, try changing the safety barrier, it should solve it.
Using isolation barriers might be a good idea. From the perspective of the CS3000 software, there is no performance difference between the display function block and the control function block. Did you say that the original multi-point card was moved to a single-point card? It is possible to improve this. Single point card performance is indeed better. But from your description, it shouldn't be a card issue. Another point is that the temperature card should generally be installed on the Node at the bottom of the cabinet, otherwise the performance and accuracy may be affected by temperature changes in the cabinet.