The thermocouple temperature rises suddenly and then returns to normal immediately – what could be the cause?
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Problem description: The temperature fluctuates suddenly from around 450°C to around 600°C, and then immediately returns to 450°C; this sudden fluctuation directly causes the shutdown. The circuit, from the field to the control room, consists of: K-type thermocouple, temperature sensor, safety barrier, and card holder. Handling status: All terminals in the entire circuit have been tightened on one side, and no obvious loose connections were found anywhere during the process. Even if the wiring of the thermocouple is disconnected, the temperature change will be measured at 0 mV; the temperature cannot rise – instead, it should drop. Therefore, even in the case of a loose connection there, it will not trigger an overtemperature alarm that causes shutdown. Additionally, if the 4-20mA signal circuit between the temperature sensor and the safety barrier opens up suddenly, it is unclear what reaction the P+F safety barrier will have Should a strong signal be sent to the card to trigger interlocking? Or there may be other reasons; please analyze it.
1. If the input terminal of the P+F safety barrier is open-circuited, what signal does the safety barrier send to the card? 2. If the circuit between the safety barrier and the card is open, how does Honeywell’s SIS respond – by causing an overreport at that point? ? ?
Based on my personal experience, the configuration in the automatic control system should be set up to trigger an emergency stop in case of a wire breakage; it’s recommended to check the relevant instruments to take a look!
I think it’s because in DCS the temperature signal lost its setting for a maximum value, and that’s why the system stopped
1. I’m not sure what type of safety barrier you have on site; if it’s an MTL type, it can be set to output the maximum or minimum value when the input is open circuit. 2. In the SM configuration software, it is possible to set the fault reaction in the properties of the AI point
1. If it is confirmed that the components are all fine, check the wires. Check if there are any large pumps or something nearby that got started at that time. 2. If active configuration is available, add a half-second delay after the signal (determine the exact duration based on actual conditions) to serve as a filtering effect. 3. Nowadays, most systems come equipped with disconnect protection; in the event of a signal failure, the system’s output is locked at a certain normal value while an alarm is triggered. Check to see if this function is available. 4. Check the P+F safety barrier carefully. I’ve encountered situations where the output of a P+F safety barrier would gradually increase from 0 to 100 on its own; it took me a long time to figure out that the problem was related to the safety barrier. This is my personal opinion for reference only.
We are using the Kangjisen system; it features heat resistor input. With the P+F temperature sensor, the reading jumps to its maximum value before returning to normal. There was only one such instance, and later we replaced it with another P+F temperature sensor