Is a relay needed for the DO signal of electric valves?
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Hello everyone, I would like to ask whether a relay is needed for the DO signal of electric valves (the signals from the system that control the opening, closing, and stopping of the valves) Thank you
It is best to add a relay for electrical isolation.
Okay, thank you. I see other engineers not using relays.
Electric valves are controlled by electric actuators, which contain relays inside; therefore, there is no need to add additional relays in the wiring. Only when valves (whether pneumatic, electric, or hydraulic) require emergency start/stop in an interlock system, in addition to waiting for the interlock to initiate such operations, can a relay be connected to the DO signal allowing direct control via an emergency start/stop button. If electrical isolation of the signal is required to prevent interference, an isolator should be used.
I see, thank you. Got it.
The DO signal of the electric valve (the open, close, or stop signal from the system to the valve) is a level or pulse control signal for the actuator. In the case of the ROTORK electric actuator, a level-holding signal is typically used to control its start and stop; this can be achieved by utilizing either an internal 24V power supply or an external 24V power supply, with a passive dry contact forming a circuit that leads to 0V. This dry contact can be a regular button, or it can be a DO point from a PLC or DCS system (of the relay output type), or it can be the contacts of an intermediate relay. In summary, the controller of a conventional intelligent actuator functions like a PLC: the start/stop signals are DI inputs, while alarms and status feedback are DO outputs.
For the command input of MOV, relay isolation is generally not used; instead, optoelectronic isolation is employed. The status output of MOV is isolated by a relay. Setting a relay can improve resistance to interference ； Prevent accidental connection of 220V terminals at the site, which could cause voltage backflow and lead to smoking of the circuit board.
A relay must be used for DCS remote control; without a relay, how can a dry contact signal be output from the DO channels?
I personally recommend adding it – many companies’ modules or expansion boards come equipped with relays! Let’s talk about whether it needs to be added, taking into account the system you use. If there’s enough budget, just add it directly