Fault Light

Tarheel · Jun 26, 2007

Hi I was wondering if anyone knew how to set up a fault light, namely my Chasis will be locked away and I want to set up a light to tell if the program is running properly.

harryting · Jun 26, 2007

<IF FAULT = YES, TURN ON LIGHT>

The quality of the answer depends on the quality of the question

curlyandshemp · Jun 26, 2007

Tarheel said:
Hi I was wondering if anyone knew how to set up a fault light, namely my Chasis will be locked away and I want to set up a light to tell if the program is running properly.

What type of PLC?
If Clgx, you can use the GSV instruction to get the status of the CPU and display this on an HMI.

If not, an output to a relay, where the NC contact is wired to the fault lamp. As long as the output is ON, the fault light is OFF.

Ian

Tarheel · Jun 26, 2007

Sorry to clarify, I am using RSLogix 500, and a SLC 500 1747-L531, on the processor box there is a LED which tells you when there is a fault and I want to emulate this on a larger scale. I was wondering if there is a command in RSlogix that tells you either "yes fault" or "no, no fault", so I can output it to another light.

Tarheel · Jun 26, 2007

Actually I believe i just found it, S:1/13 says there is a fault I believe?

OZEE · Jun 26, 2007

If there is a fault that has lit the light, the processor has stopped scanning the program. How is it going to be used to indicate anything?

Unless you set an output to always-on, then use a relay to light your indicator. Light connected to the NC connection. Like curlyandshemp said.

Trust me, you'll know if you have a PLC fault. It'll get real quiet...

allscott · Jun 26, 2007

I would wire a light through a normally closed set of contacts on a relay.

Hook the relay up to an output and program the output to be always on.

If the processor faults or goes out of run your light will turn on.

edit: Yea like he said

Hakutsuru · Jun 26, 2007

I always do it slightly different with AB PLCs. I wire a light directly to an output which I turn on in the logic. Then I label the light "PLC OK". If the PLC stops running for any reason, that light goes off. I think that S bit will only work for you if you are reading it from an MMI. Not sure if it will work as intended if you try to use it to turn on an output. It might if there is an option to have the outputs hold thier last state when the PLC stops, and you make sure that rung is the last one in the program. But even then, aren't there some faults that will not finish the scan before everything stops?

-jeff

OkiePC · Jun 26, 2007

For an incandescant lamp, Hakutsuru has it right. All local outputs should turn off when the processor fails...there are exceptions, but usually not in the local rack.

For an HMI indicator, you can read the first five bits of S:1 in a SLC to determine the processor status. I don't have the bit patterns handy, but there are many possible modes: RUN, Remote RUN, Program, Test. You should look at the channel status for the channel you are communicating with too. If S:1/00 through S:1/04 are in the correct state AND the comms channel is healthy, you can report that as a "Program Running" condition on the HMI...

TConnolly · Jun 26, 2007

Placing S:1/13 in your ladder logic will have no effect. Were I to see it used in a program I would think that there is something that is very fundamental about PLCs that the programmer was not grasping. Use an unconditional output as has been suggested.

Hakutsuru · Jun 26, 2007

Is there any use for S:1/13 in the ladder? Like to call a fault routine? Or do you think they just have it in there so another device can poll for the status?

-jeff

TConnolly · Jun 26, 2007

If S:1/13 is set the all program processing, including subroutines and interrupt routines, is halted and all IO is set to the default state. The status of S:1/13 can be read by or written to by any device communicating with the PLC such as another PLC or PC.

In a couple of RSView apps I created a PLC status screen that indicated the PLC status, error code, and had the ability to clear a fault and return the PLC to run mode.

Fault Light

Tarheel

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