Problems with operating the control valve via the DCS and solenoid valve
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In the Zhejiang University Zhongkong DCS system, pneumatic control valves equipped with solenoids mean that once the solenoid is turned off, the valve ends up in an emergency state of being fully open or fully closed. However, it is still possible to enter values on the DCS interface; in reality, the valve can no longer be controlled. Is it possible for the DCS to prevent value entry after the solenoid is turned off?
At this point, the valve signal should be locked by interlock; even if you enter values in the input field, it will have no effect on the valve. The effect on the valve is that, after the interlock is reset, since there is an input value, the valve will change its opening degree according to that input. Therefore, after interlocking, related similar valves should change the output value of such valves to a safe state (fully open or fully closed).
Additional control methods include manually locking the solenoid valve on-site (depending on whether it is powered or not), to turn it on or off. Locking of the switch can also be implemented on the valve body, for reference.
Senior, I need to mention this: the action you’re referring to is usually taken when it’s confirmed on-site that a valve isn’t functioning properly. Under normal circumstances, it’s not allowed to change its status on-site without authorization; such an action is considered a violation of regulations! ;P
Oh, maybe it’s because of the levels of equipment I’ve seen so far – no such standards have been established yet. But in emergency situations, any measure must be taken as long as it helps prevent the fault from worsening:D
This requires writing a program that uses logical statements to lock the PID block and fix the output value at the opening degree of the faulty valve (0 or 100), thereby ensuring consistency with the actual conditions on site. Once the interlock is reactivated, it unlocks automatically, but the original output value remains unchanged to prevent large fluctuations
The interlock system of my previous setup did not have the functions you mentioned; after replacing the setup, the existing interlock system can now perform those functions, **reducing the likelihood of human errors and ensuring the safe operation of the setup.
This solenoid valve has lost power; the air supply has been cut off. Even if you set a valve position, it won’t move. It shouldn’t cause any problems, right?
Yes, new employees often overlook this relationship; as long as a value can be entered for the valve, they assume that the valve on-site can still operate