FactoryTalktotheHand
Member
Its a different contacts from different controllers all of them have a emergency stop and the variety is expanding all the time. I think a plc would be the best option. How do i now how big plc i need like memory when the program is getting bigger and bigger?
I would at the very least use a Programmable Safety Controller as opposed to a PLC. The reason is PSCs have their own power loops for inputs (called Test Outputs). These TOs periodically drop voltage at a regular interval. Each TO on a controller does it at a different rate. When you program the controller, you specify which TO each input is reading from, and typically for an E-Stop each contact comes from a different TO.
This way, you're not only testing the E-Stop, but the entire E-Stop circuit. Without Test Outputs, you have no idea if the circuit loop is actually being closed or if someone is just applying 24vdc to it at some point, bypassing the E-Stop. It's also a way to prove that the E-Stop is indeed wired by two completely independent channels as opposed to being jumpered at the button.
I'm not sure if this would be of any help to you or not, but that is my recommendation. I've used the Omron G9SP series before which are expandable, inexpensive, and quite easy to work with.