New to PLCs

Hello all,

I have been designing Functional Safety systems with Safety Relays, but for a new system I might consider a PLC as there are additional I/O requirements.

My questions are:

1. Can a safety-rated PLC replace safety relays - can they do pulse testing of emergency stop circuits?
2. Does monitoring of force-guided contactors have to be programmed separately?
3. Does anyone have experience using OPC-UA to interface with Python to read inputs and set outputs from a PLC?
1. Yes, a safety-rated PLC can replace safety relays, including pulse testing of dual channel inputs. Depending on your requirements on the output side you may need additional relays compared to a safety relay for the loads you are isolating.
2. Generally there are approved program blocks that are equivalent to the functions safety relays can perform, you just connect the inputs and outputs required. This would include an output block for a contactor with feedback
3. No experience with OPC-UA to python, though generally you would be reading and writing to a data area not directly to IO. You would read/write bits of data in the plc program and these could read/write to IO
There are simpler “configurable” safety systems compared to a full safety PLC which may meet your requirements, eg Sick Flexisoft