Safety Interface Method

I am looking to interface a control system we're designing with another piece of equipment. I will be using an S7-1500F (failsafe); the other piece of equipment uses a proprietary control system.. This will be a simple I/O interface, but some of the signals will be safety signals (e-stops, machine inhibits, etc.).

I've built interfaces in the past between machines, but never involving safety signals. Most of the signals will be through a bank of relays, but I'm not sure what to do with the safety inhibits. For example, the e-stop input from the other machine will input into a failsafe input card in my PLC, but I'm unclear what to do in between. I'll also need to feed an E-stop signal back to the other machine. (The other machine uses a safety relay for e-stops)

Just a side note.... I'll be using AS-i elsewhere on my system (also failsafe). Proximity to the other machine's controls makes it unnecessary to use AS-i for the interface, but I could use it if it makes it easier.

Safety is only as strong as its weakest link. You need an unbroken chain of safety-rated components from beginning to end.

First, what is your required SIL rating? Is the other machine rated at that SIL or greater?

You say that the other control system has a safety relay for emergency stop. If so, the simplest approach may be using a safety-rated interposing relay from the S7 in series with the 'local' e-stop switches. Hopefully there is another contact available on the safety relay to use another safe coupling relay to feed back to the S7.

You will also have to recalculate the PFHd for the new configuration.

You can have an ECR(estop control relay) that is shared between the machines. It sounds like the machines are local to each other. The ECR will supply power two your outputs on both machines and also a logical input. If the logical input fails your outputs will loose their supply power even if still high in the logic. It would be best if the estops physically drive the ECR and not a logical input. Sound possible?