Reverse state of output, can't change logic

[eternalphoenix64]

I'm trying to add on to a safety circuit and trying to make sure this is fail-safe. My safety scanner needs some muting when things aren't running so that employees can still do their job without having to reset the machine a dozen times an hour. Problem I'm having is that the muting input(s) require NO, and I'm basically setting up NOHC, but I need to hold closed when all my outputs are 0, and stop holding if any become 1.

I can swear that I've used them in the past but I can't seem to remember what they're called. I could have sworn there's a device that will reverse the state of an output (making a 1 a 0 and a 0 a 1). I have 15 outputs to do this on, and I can't change the polarity in the PLC or else nothing will function (I also am pretty sure we don't have TIA Portal, but I'm still fairly new at this company and just might not have asked the right people yet).

Anyone have any devices they can point me to or suggestions for search terms? I keep getting results that are pointing me to changes in logic, which I can't do.

 

[kamaroman68]

Can you use a simple relay? x 15? wire the coils to your existing plc logic and use the NC/ NO contacts as needed. Example coil is off NC is made, and vice versa.....

 

[eternalphoenix64]

Can you use a simple relay? x 15? wire the coils to your existing plc logic and use the NC/ NO contacts as needed. Example coil is off NC is made, and vice versa.....

That seems to me as though that would not be fail-safe. Because a failure of the relay or output would cause the relay to fail-closed instead of fail-open.

 

[kamaroman68]

True..... I actually wasnt considering the safety part of it... my fault

 

[eternalphoenix64]

True..... I actually wasnt considering the safety part of it... my fault

All good. It's the same thing I keep butting my head against and keep failing with. I have gotten excited about using NC relay contacts more times than I care to admit and I'm the one working on the problem, lol.

 

[5618]

For a relay inversion, maybe you could use something like one or two force guided Omron G7SA and include monitoring in the safety system.

Are you using a safety PLC? I'm not familiar with Siemens safety, but adding a module or rack of safety outputs could be easy-ish and clean. But that involves reaching and changing the program...

 

[eternalphoenix64]

For a relay inversion, maybe you could use something like one or two force guided Omron G7SA and include monitoring in the safety system.

Are you using a safety PLC? I'm not familiar with Siemens safety, but adding a module or rack of safety outputs could be easy-ish and clean. But that involves reaching and changing the program...

No safety PLC, not that I'm aware of, at least. I haven't gotten with maintenance yet to get me the key so I can open the panel and look inside, but part numbers indicate it's a normal Simatic S7.

Can you give me a layman's summary of what the force guided relays are/how they work? I'm looking them up but also working on some jig designs in Solidworks while waiting on responses and my brain is sluggish this morning. It looks like they're a sort of "light switch" but they can be tripped off by the safety relay? Is that about right?

 

[5618]

As far as force guided, if you're familiar with safety contactors for motors that have the monitoring contacts mechanically linked to the main contacts, these relays are about the same thing except smaller.

A basic safety system to me has two contactors in series that drop power to whatever creates the hazzard. The monitoring contacts are mechanically linked to the main contacts. If one of the main contacts welds on, the monitoring contact won't close when e-stop is activated. The odds of both contactors welding on at the same time is low enough that for this I'll say the other contactor didn't weld and dropped the power to the hazzard.

Since the monitoring contact didn't close on the contactor that's welded, the safety controller doesn't see that required input and won't reset, requiring maintenance to investigate and repair.

 

[Jeev]

If you don't want to use a relay then have a look at different Signal Conditioners or Signal Converters from various vendors. I'm pretty sure Balluff has the thing you are after though. It's an inline configurable signal converter.

https://www.balluff.com/en-gb/products/BAE012T