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JackE

Safety Inputs/Outputs

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Hi,

 

How do I address safety inputs and outputs from the safety PLC to my main PLC program?

Usually I'd use a PILZ relay to drop out coil&main power to contactors and then control contactors from my PLC, however someone else has designed this machine so there is a safety PLC which I have to turn the contactors on through the safety PLC.

 

So the inputs from the safety PLC and outputs from the safety PLC need to be read + written to from my main ladder logic....is this possible?

 

Also - using a variable in my main PLC program in the safety program, is this possible?

 

I want to use my 'Safety OK' + a variable from my PLC to turn on a Relay (which is connected to a safe output)

Edited by JackE

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Edit - managed to do it. Omron tutorial isn't relevant any more.

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Only the safety PLC can write the safety outputs.  But the status of the inputs and outputs is all visible in the PLC by default.

From the PLC, you can send data into the safety controller using Exposed Variables in the safety controller. 

They should never be controlled from the main PLC, they should be controlled in the safety controller's program.  PLC addresses can be modified and forced, where safety controllers prevent this type of access. 

Doing it the way you mentioned will not pass any category of safety standards.

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