Hello everyone,

Has anbody ever had to assemble a current or voltage sensing relay. My situation in which I require it is as such. I have a master slave configuration wired together using a four conductor cable. Two of the wires are for RS 485 communication and the other two are power from the vicinity of the slave feeding the master. The current is currently switched on the hot side of the master PLC. In other words +12VDC from the area of the slave enter the comm/power cable and connect to a SPST switch then to the PLC and the ground or 0VDC is fed back to the vicinity of the slave via 1 of the remaining 3 conductors in the cable. What I need to do is sense this current and drive a relay that powers the slave. I hope this makes sense, if anyone can help me out it would be greatly appreciated.

Thanks,
Ken Talley

 

Check out
http://www.gavazzi-automation.com/ac/acfront/controlmonitor.htm

Meeuwis Bouw
Flamco NL

 

How about using one of the contacts in the master PLC to turn on when you power on the master PLC. This contact would only be on when there is current in the circuit you describe.

 

My problem is that I have only four conductors linking the two plc's and the power (12vdc) is located at the slave. 2 conductors are communication and the other two power and with out sacrificing a dependable ground and grounding through chassis I know of no other "signal" which could tell the slave to turn on.

Thanks,
Ken