AB Safety PLC questions

Hello,

I have a tiny bit of experience developing with Codesys on Eaton plc's.

I'm being asked to look into a project that is NOT well documented. It's an Allen Bradley system. What makes it more confusing for me is not understanding the topology of the safety system used. In my previous work, we used a separate stand alone safety relay.

This system uses 1734-IB8S safety modules in the normal PLC. Based on a layout drawing of the panel, there is a separate CompactLogix Safety PLC. I can see in the wiring diagram where the E-stop buttons are wired on the safety modules, and have no documentation on how anything was implemented.

Would those IB8s modules communicate with the Safety relay, with it's own program? Would that Safety PLC control outputs on the other PLC such as the one for the MCR?

I know, more info is always better. Unfortunately, I just don't have it. I'm beginning to think I don't have enough info for what they're wanting. Just wondering how these systems are normally setup in an overview kind of sense.

Someplace in the system you should have some safety output modules. The safety PLC will have a separate section of logic for reading the safety inputs and controlling the safety outputs. It could be as simple as making it look like an e-stop chain, or could be complicated as you pretty much like. The safety task can be locked, and if it is you can't edit either the logic or data, or force safety things, until it is unlocked.

The safety inputs and outputs can be read anywhere in the PLC, but the safety outputs can ONLY be written to by the safety logic. The safety logic can't use non-safety tags, only tags that are safety type, and you can't write to safety tags outside of the safety logic. You also can't write to them from an HMI. You can map tags into the safety logic (for example a signal from the HMI) using the "Map Safety Tags" function on the "Logic" menu.

With a safety PLC there isn't usually a stand alone safety relay.

kenschunk said:

Someplace in the system you should have some safety output modules. The safety PLC will have a separate section of logic for reading the safety inputs and controlling the safety outputs. It could be as simple as making it look like an e-stop chain, or could be complicated as you pretty much like. The safety task can be locked, and if it is you can't edit either the logic or data, or force safety things, until it is unlocked.

The safety inputs and outputs can be read anywhere in the PLC, but the safety outputs can ONLY be written to by the safety logic. The safety logic can't use non-safety tags, only tags that are safety type, and you can't write to safety tags outside of the safety logic. You also can't write to them from an HMI. You can map tags into the safety logic (for example a signal from the HMI) using the "Map Safety Tags" function on the "Logic" menu.

With a safety PLC there isn't usually a stand alone safety relay.

Click to expand...

That information helps a lot. It makes sense that there wouldn't be a stand alone relay with a safety PLC. It also makes sense with what you said about safety outputs .vs non safety outputs. I can see the MCR is wired to a standard output, but maybe that is mapped as a safety tag. I've also found that the VFD's are capable of safety stops without powering down the drives.

Ultimately, that makes it seem like I really can't do what they're asking without access to that portion of the programming as well.

Thank you.

"MCR is wired to a standard output"?? I suppose you could do that, but it wouldn't be safety rated at that point. The VFD's may have Safe Torque Off (STO) signals that can do a safe off, but you'd want to see how that is configured.

The good news is that the safety stuff is programmed with regular Logix 5000, so you should be able to at least look at the safety part if you can look in the PLC. You may be able to change it if it wasn't locked with a password.

Note that although you can look at safety logic with any version of Logix 5000, it requires a Professional or Full edition, or separate GuardLogix Safety Editor, if you want to make changes.

plvlce said:

Note that although you can look at safety logic with any version of Logix 5000, it requires a Professional or Full edition, or separate GuardLogix Safety Editor, if you want to make changes.

Click to expand...

I program a Compact Guardlogix 5380 with Studio 5000 Lite as the safety editor is included in Lite. I also have a Mini license and it does not function on that license of course. I can view but I cannot edit.

You are correct, Lite also supports safety editing. Not sure how I'd missed that, my apologies. Thank you for the correction.