DCS signal issues for electrical systems
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I have a question: The DCS provides two DO signals for the electrical system. These two DO relays of the DCS – when a start command is given, the relay switches on and then turns off; whereas the stop relay, which was in a normally closed state, switches off first and then turns on again. I don’t understand this!! I don’t understand electricity! ! ! Could some expert explain it?
It’s either possible or it’s a pulse. What I don’t understand is why, when the shutdown command is given, the relay goes off for a moment before staying lit
I suggest you check out the wiring principle of the cabinet, understand the concepts of normally open and normally closed circuits, as well as whether there is any interlocking mechanism; it’s not possible to determine what’s going on just by looking at it in person
This needs to be understood in conjunction with the electrical diagram; generally, the start switch sends out a pulse, and the electrical circuit uses coils in parallel to achieve self-holding. The stop switch, on the other hand, is connected in series within the circuit – it is disconnected to stop the motor, and then reconnected so that the motor can start again next time.
Well, I asked our expert today, and it’s just as you said – this is referred to as applying a negative pulse in DCS
The weather is nice today, let me explain it to you. Firstly, the relay is configured for accident safety, meaning it remains powered under normal conditions but loses power in case of a fault. Secondly, the start is a pulse signal, and the stop is the inverse of a pulse signal. Again, if it stops with interlock, startup is a pulse signal, and stopping is the inverse of the pulse signal plus a low-level signal (interlock).
This should be the start/stop signal. The self-lock is inside the electrical cabinet.
It depends on the electrical control circuit diagram. Generally, the stop signal is normally closed, while the start signal is normally open. The instrument sends an electrical pulse signal (usually for 3 seconds), that is, a start signal; use a multimeter to measure it – it remains connected for 3 seconds before being disconnected ； The stop signal means to turn on, then disconnect for 3 seconds, and finally turn on again. The self-locking circuit is implemented in the electrical control cabinet.