Circuit for plugs state check

Hi,

As a beginner I cannot decide what way would be best for the following:

I have a panel and some machines, all connected with 5 plugs which can be unplugged. I will use one input on the PLC to see if any got unplugged.

Considering the following options:

1. To run one line through everything:
http://tinypic.com/r/15n28pk/9

2. To use some relays/contractors, ex. 24V goes through all plugs into a relay, and some contacts break the circuit on the PLC output? This makes sense but cannot figure how to connect it all.

Thanks!

Option 1 is preferable if the cable runs aren't long and you don't need to worry about voltage drop.

Otherwise you need to drive a relay from each plug then connect NO contacts from each relay in series to the PLC. That gives the possible benefit of knowing which plug is unplugged.

How many spare ways do you have available in each plug?

I was thinking the same, the cable will be around 5m, at 25VDC the loss will be around 4VDC, which is good for the PLC input.

In theory looks good, was not sure about practice.

The only downside to using a series loop to a single input would be troubleshooting. You know you don't have the input, but you don't know exactly which of the plugs it stops at.

If I have the room for multiple inputs, I always choose separate instead of series. Or at least monitoring of some sort to make it easier to determine which one the signal stops at. Maybe something as simple as a paralleled LED after each plug in the loop.

It would be helpful to know what signals are routed through these plugs. If it is something like 120vac power, then using a current monitoring relay in the main panel might give you the indication you need without any extra any pins and could tell you there was a problem even in a case where a wire breaks inside a connector or cable.

I agree that having a separate input per machine would be beneficial if you have the space for it.