Joe's 1000x600x200 steel and aluminium router started

[devmonkey]

Thanks guys, lots of inspiration here.

The DDCS has two estop inputs but one is difficult to access on the MPG port. I have an idea how to sort this now. Currently I use the output of the safety relay to switch the low side of the contactor coil and also signal low to the DDCS estop input which is configured to go into emergency stop if this signal is high. I was looking to integrate the alarms on the estop switch side of the safety relay but this is wrong, instead I can put them on the output side. Take a resistor to +24v then series the NC alarm outputs via the same safety relay contact to ground. Take the DDCS estop input from the resistor.

With this configuration the alarms will only estop the DDCS not the contactor, but when the safety relay is tripped both DDCS and contactor will estop. Million dollar question, do I need a diode to prevent current flowing from emitter to collector through the alarm NPNs into the DDCS input when the safety relay is open? My analogue electronics is extremely rusty.