AC700F completely stopped trending when max temperature was achieved
The inaccurate readings have occurred, it would suggest that the issue is with the DCS system. We have performed as much testing internally as possible with no avail. What are the next step to be taken in order to rectify this issue?
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No - its probably not just "the DCS"
The DCS is simply an A-D convertor that converts the thermocouple current to a Digital Value. The DCS I/O card is part of a complete signal loop that also includes the thermocouple, the cold junction and the cabling.
There seems to be 2 separate issues here ....
- The measurement is not accurate. This is 99% likely to be the thermocouple installation and not a bad IO channel. Its likely the same mistake is made in all 3 thermocouples.
- The signal quality goes bad when the signal reaches its max limit which causes the historian to stop recording. This is probably a DCS or historian setup problem.
I assume/consider that you have configured those channels properly. CJC - compensation is configured correctly. If all that is correct then please test\simulate those channels first by using some external mv source. Ensure that cabling and scaling and configuration is right. And once that part is done. Then it remains on field instrument. DCS will show what is coming from Field.
So I propose to check/test/simulate those channels first to ensure DCS side it works fine. and secondly check field instrument calibration if there are any issues.
Hope that helps...