Is there frequent and severe fluctuation at one temperature point in the PKS system?
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One month after the PKS system was successfully commissioned and started operating normally, a temperature reading began to fluctuate frequently. The field element is a thermocouple with an integrated temperature range of 1200, which is then connected to the isolator via a shielded cable and fed into the DCS. Since it is a cascading temperature effect, the value set for this cascading effect is relatively low, around 600. However, whenever there is a fluctuation, values of 900+, NAN, and 1100+ appear one after another; this situation lasts for about 2 seconds before returning to normal. But a parking accident has already been caused. Subsequently, the temperature sensors (thermocouples and temperature detectors) were replaced one after another, and the isolator was also changed; however, stability was achieved only for 2 days after the temperature sensors were replaced, after which fluctuations reappeared. Even after replacing the isolator. Now it happens basically every few hours. Filtering was added at first, but the effect wasn’t very good. Now a warning dead time has been implemented temporarily, in the hope that this will yield better results. I analyzed the reasons: 1. The high temperature at the site caused instability in operation due to temperature changes. However, the temperature at this point is not the highest; at other points where the temperature is around 1000 as normal, this phenomenon does not occur either. 2. The shielding wire is not properly grounded. The cable shielding wires in each cabinet are reliably grounded. Although the grounding resistance has not been measured actually, considering that this is not the case at all other points, it should not be a problem with the shielding or grounding. Everyone is welcome to discuss and share their opinions.
Our unit also encountered a similar situation: incoming ESD-related signals caused large fluctuations at irregular intervals, which led to the device tripping accidentally. It is recommended that you check whether there are high-power electrical devices nearby the instruments that could cause interference, or whether the power cables and instrument cables are laid together in the cable trays; additionally, the grounding system should be checked again.
In your cabinet, have the other available terminals on the FTA connectors related to those wires been shorted together? Is the circuit board grounded? These two factors can also cause fluctuations in microvoltage, which in turn leads to temperature variations.