Everyone, do you think such a modification is okay?
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There is an electric door that was originally supposed to be activated and stopped using a 5-second pulse signal from the DCS system. However, during testing it was found that the door wouldn’t open or close properly when such pulse signals were sent, as the door itself did not have a self-locking mechanism. To ensure the proper operation of the electric door, it is necessary to convert the pulse signals from the DCS into continuous signals. However, I am concerned about one issue: when pulse signals are used, the relay contacts remain charged for a short period of time. If continuous signals are used, the relay contacts will remain charged for a longer duration. Given that the voltage in the relay contact circuit is 380V, do you think this modification is feasible? If that’s the case, is there any danger?
Properly extending the 5-second pulse signal ensures that the electric door opens and closes fully, but the duration should not be too long; such a modification is safe. However, it is best to add a self-locking circuit to achieve unlocking using the feedback signal from the position of the electric valve.
This post was last edited by zlwjinzhou on 2011-3-22 09:59. Personally, I think there should be no problem. The current must be within the allowable range of the relay contacts. Question: Electric valves should all have a valve position feedback signal, right? (Otherwise it could damage the actuator.) Can pneumatic valves be used with delayed shutdown without a valve position feedback signal? Ask an expert
It is indeed dangerous to have a 380V voltage applied in the relay circuit; the concern here isn’t related to the relays themselves – as long as the right type of relay is chosen, there should be no problems. The main worry is electric shock during routine maintenance, so it’s essential to provide proper warning signs for those relays； To ensure that the relay does not remain powered on for an extended period, the valve position feedback signal from the electric valve can be incorporated into the control circuit. First, measure the full stroke time of the valve under normal conditions; for example, if it is 100 seconds, you can develop a control scheme based on this value. In this scheme, the valve opening signal should be linked to the valve position feedback signal – that is, the valve opening signal should be disabled once the valve position feedback signal indicates that the valve is fully open. Another consideration is handling fault conditions: if, after 110 seconds since the valve opening signal was sent, the valve position still has not indicated full openness, then it is considered a fault condition, and the valve opening signal should also be disabled in such cases ； This way, it is possible to prevent the relay from being exposed to 380V voltage for long periods of time. Another solution is to use a delay relay in the control circuit on the electrical side, setting the delay time to be longer than the full stroke time of the valve; this allows us to use a 24V control signal, with the entire 380V circuit remaining on the electrical side