Feedback signal, please help me, experts!
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Today, a butterfly valve needed to be replaced. While performing the debugging after the replacement, my finger went numb. Upon further inspection, it was found that the drive solenoid operated at 24VDC, while the feedback signal from the valve body itself was 220VAC. Since I had been working with dry contact signals in the past, I would appreciate it if someone could explain to me what this 220VAC means!
It makes no sense. For module requirements, if you’re worried about electricity, it can be changed to 24V. The key question is why do you need to touch it?
The feedback I encountered before was from dry contacts; since that feedback device needed to be replaced, the power wasn’t turned off while the wires were disconnected – 220 volts is extremely dangerous.
24V drive. Where did you get the feedback regarding 220V? A card holder?
Generally speaking, for this 220VAC system, there are fuses inside the cabinet, right? Just check to see if there are any fuses; if it’s a separate fuse, then simply disconnect it
The feedback is a dry contact; the issue is that it is connected to a circuit, and a 220V AC power supply for that circuit is also possible, as that’s how the relay coil needs to be driven.
It’s connected inside the relay; the relay operates at 220V, and from there the signal is sent to the card. It might be a requirement for the card.
That’s correct; it’s connected to the relay. I’m continuing to investigate, and the signal sent to the DCS is also 220.
In principle, there are no dry contacts; to determine the status of a contact, power must be applied, it’s just a matter of voltage level and the number of transmission stages. Therefore, during maintenance work, one must either be aware of this in advance or adhere to the principle of on-site testing to ensure safety.
First, find out where the 220VAC supply comes from. Unless there are special requirements, 24VDC is generally used as it is safer. Dry contacts can be either passive or active; you will need to check the original design for this information. Numb fingers are a minor issue, but electric shock is not something desirable