Allen Bradley GuardMaster Relay Monitoring

[Gadelric]

Team,

I have had some issues with my MCR dropping. This is an issue that has been in 2 of my lines prior to me coming to this facility. The maintenance staff informed me that when they drop MCR, they do not get any alarms. They thought it was a problematic e-stop and would go giggle the wires until the MCR would turn on.... monkeys with hammers I tell ya...


I was able to catch this issue this morning when I came in to support start up. I let the maint staff do what they usually do, so as to get an idea as to what might be the problem. After they did their wire giggling with no resolution, I stepped in and started ohming out the system.

I was able to deduce that one of the control wires through the e-stop on one of the ops was having issues, upon opening up the e-stop box, there was in fact a terminal that was broke. Upon fixing the broken wire, we got MCR Power back.


Now that I have power to my line, I have a strong desire to not have to climb through these station boxes again.

The e-stop circuit is monitoring for a True value, which in turns drops MCR and throws an HMI Alarm for OP_XXX_ E-Stop, this is easy to find.

The guardmaster is not monitored, when we drop a connection in the line for the guardmaster, its all hands on deck digging through boxes to find the lost signal, as each station is daisy chained to the next.

I would like to monitor the output side of each station's guardmaster circuit.
I have fears that running a leg off of the output side of the circuit to the PLC will cause issues with the circuit. I have been told that there is a pulse modulation that the guardmaster pushes out and monitors on the feedback side that can get angry if you try to mess with the circuit.

Any advice, or things I should watch out for?

 

[Picklemon]

Gadelric,

I would definitely not wire a PLC input into the safety wiring circuits.

Depending on which model safety relays you are using, there should be a transistor output designed for PLC monitoring. It's labeled Y32 on all of the GuardMaster relays I've used recently.

https://literature.rockwellautomation.com/idc/groups/literature/documents/wd/safety-wd001_-en-p.pdf

 

[Vlad Romanov]

I have been told that there is a pulse modulation that the guardmaster pushes out and monitors on the feedback side that can get angry if you try to mess with the circuit.

This is definitely correct. Do not connect the signal legs of the GuardMaster back to the PLC.

Each relay of this family has dedicated PLC output legs which are just a set of open/closed contacts; they are labeled "To PLC" in the manual. See reference: https://literature.rockwellautomation.com/idc/groups/literature/documents/um/440r-um013_-en-p.pdf

Alternatively & even better solution if you have an array of these would be to use the ethernet module: 440R-ENETR. IT will give you the status of each module & much more over ethernet.

Good luck,
Vlad

 

[Gadelric]

Thank you for the assistance, I will look at the options that have been given and see what kind of capital we can throw at this thing so we can prevent this issue from causing excessive downtime.

 

[Vlad Romanov]

Thank you for the assistance, I will look at the options that have been given and see what kind of capital we can throw at this thing so we can prevent this issue from causing excessive downtime.

Sure thing. If you have a schematic or part number it should be very simple to tell what needs to be wired in. In terms of cost, it should be just the labor to install the cable back to a PLC input. Except of course if you have none available.