A-B 1746-1A16, can I add a relay coil?

Are there possible deleterious effects (bad things) that can happen if I add an external 120Vac relay coil as shown on the sketch above?

I need dry contacts that logically follow the switch state for another analyzer but I'm not sure if connecting a coil as such might do harm to the PLC input. I'm told that they're pretty fragile.

Roywarren said:

Are there possible deleterious effects (bad things) that can happen if I add an external 120Vac relay coil as shown on the sketch above?

I need dry contacts that logically follow the switch state for another analyzer but I'm not sure if connecting a coil as such might do harm to the PLC input. I'm told that they're pretty fragile.

Click to expand...

I think transient spikes may be an issue.

You could also have the input signal activate the coil isolated from the input, and use another set of contacts for the PLC input

I have seen this done before, but I also am not sure if its a good idea.


It would probably be better if you can have the input directly energize an output through the plc logic and energize your relay from the plc output.


Derek

Follow curly's advice. The simple solution is to have the input energize the coil instead and use two sets of contacts, one for the input and one for your other device.

While controlled's advice would work too, you are then relying on the PLC to be operational for your other device to read the state of the switch which may or may not be a disadvantage.