modbus or hardwire?

[can]

hi. If i need a 2 conditions of 888 (1) to be on in order to activate a process controlled by 888(2), before activating 888(3) when few conditions are satisfied. So there will be a total of 3 888 talking to each other. Should I use modbus for them to communicate or should i wire one of the output of 888(1) to input of 888(2) in order to have quick response? Thanks.

[support]

If PLC 1 is to trigger PLC 2 and PLC 2 then trigger PLC 3, you'll need PLC1 to talk to PLC 2 and 3 (one master) via RS485 using Modbus. PLC1 need to monitor PLC2 status and then activate PLC3. Modbus via RS485 will work. But of course hard-wiring is always the fastest method. if the PLC are not too far apart you may want to use hard wiring. If they are far apart then using the RS485 serial comm will be more cost effective.

[can]

hi. Thanks for the reply. Can i connect the wire directly from the digital output of plc 1 to digital input of plc 2 if both are sharing the same power supply? Or do i have to use relay instead? Thanks.

[support]

Yes, as long as they share a common ground you can connect from one PLC's NPN outputs directly to another PLC's NPN input. If they are using the same power supply, no problem at all!