SLC500 Question

[LLSolutions]

Is there anyway to have a processor fault annunciated in a remote location. Even if it had to have its own output module with just a single binary output. Or is this just impossible do have a processor fault and be able to output it? I've heard you can do it on a micrologic

 

[Jraef]

Is there anyway to have a processor fault annunciated in a remote location. Even if it had to have its own output module with just a single binary output. Or is this just impossible do have a processor fault and be able to output it? I've heard you can do it on a micrologic

Do you want to annunciate a CPU fault in a remote rack, or do you just want a way to annunciate a CPU fault somewhere other than in the PLC itself?

 

[Wire_nutz]

How elaborate do you want to get, or how much do you want to spend.

The cheapest and simplest method would be to use a light beacon and a reset button. Wire these devices to your input/output cards and write the logic program using the fault status bit when a fault would occur.

If you want an expandable system with more visual and control. You can get a Remote I/O (RIO) Scanner Card. This would allow you to incorporate other operator interface and control devices such as Panel Views, Redi Panels, Message Displays ect.

 

[StephenSDH]

Commonly you have an output which is always energized. OTE instruction with nothing else on the rung. If the PLC is in the run mode and healthy the output will be energized. When the PLC is either in program mode/powered off/faulted the output will turn off. If the output is on you know the PLC is in control. Sometimes this output will be tied into the safety circuit to drop it out if the PLC loses control.

Or if you have a Panelview you can try to display the status of data in the S2 file.

 

[LLSolutions]

How elaborate do you want to get, or how much do you want to spend.

The cheapest and simplest method would be to use a light beacon and a reset button. Wire these devices to your input/output cards and write the logic program using the fault status bit when a fault would occur.



How do I program a fault status bit to energize an output?

 

[S'mise]

fault bits

fault bits

A Fault bit can be written like any bit or input.
-| |-----------------------------------------(out)
Fault (use a latch around fault)
Note that if the processor fault bit is used, the output often will not work. (If it stopped scanning) It's better to use a watchdog circuit in this instance to make sure the cpu is still working.

You could probably use a nc contact on a relay tied to an output to trigger your beacon light. Make the fault output a (/) "Not ote" When there is a fault, the beacon goes on.

 

[steve66]

A Fault bit can be written like any bit or input.
-| |-----------------------------------------(out)
Fault (use a latch around fault)
Note that if the processor fault bit is used, the output often will not work. (If it stopped scanning) It's better to use a watchdog circuit in this instance to make sure the cpu is still working.

You could probably use a nc contact on a relay tied to an output to trigger your beacon light. Make the fault output a (/) "Not ote" When there is a fault, the beacon goes on.

Yes, I would think if your processor is faulted, it is going to stop scanning, and the fault output will never be activated.

IMO, StephenSDH's suggestion sounds more promising.

Steve

 

[TxEngr]

The simplest method is to use an output going to an external relay. Special relays are made for this purpose, primarily for flame safety systems, that must see a changing bit. Program the output to the relay to toggle off and on at a set frequency. If the PLC stops scanning or the output bit locks to one position, the relay will sense this and time out, giving you annunciation that the processor has failed.

 

[TxEngr]

The ABB CM-WDS is a good example of the relay I was describing above. Here's the link: http://www05.abb.com/global/scot/scot209.nsf/veritydisplay/bf7303464ef6bb55c1256e4e00420250/$File/2CDC112003D0201.pdf

Other brands are available - just do a search for 'watchdog relay'

BP

 

[LLSolutions]

Thanks guys, that ABB relay seems like a good fail safe.

 

[jcole]

Stephens reply is the most economical, fastest, and reliable. So why would you buy the relay?

 

[steve66]

Stephens reply is the most economical, fastest, and reliable. So why would you buy the relay?

It would protect against other things in addition to a fault. Like if the processor gets stuck in an endless goto loop.

Not saying it would be right for every application, but it might be better for some.

Steve