Checking to see if a bit is forced in either ST or Ladder in Logix 5000

[cjnichols]

Hello

I need to have a code set up that when an particular output is forced in either ST or ladder in RS Logix 5000.

The reason for this is I need to start a shutdown sequence if only some of the IO is forced not all of them.

Thanks for any assistance

Chris

 

[cjnichols]

All

Well I am assuming by the lack of response that this can not be done or no one knows how to do this.

Is this request possible or not?

Thanks

Chris

 

[krugerf]

Forces present

Checking to see if a bit is forced Ladder in Logix 5000. In the Data tables You should find a "S" word (16 bits).
Each bit represents a status within the processor, Major error, Math overflow and uther information including forces present and enabled.

 

[cjnichols]

Checking to see if a bit is forced Ladder in Logix 5000. In the Data tables You should find a "S" word (16 bits).
Each bit represents a status within the processor, Major error, Math overflow and uther information including forces present and enabled.

Krugerf

Thanks for the post, I remember that this is the case with the old Logix 5 and 500 but this is missing with the Logix 5000.

They have replaced the System S word and you need to use a GSV "Get System Value" command either in ST or ladder.

The issue I have there is a command GSV(MODULE,,ForceStatus,Q_43_1_forcestatus); but all this returns is if there are forces enabled and forces active in the processor.

If you go back to my previous post I am looking to see if there is something simular to the GSV that I can use on a per input basis to determine if that particular input is forced.

So far I have not seen anything along these lines.

Thanks

Chris

 

[lostcontrol]

I would think that any processor that has more than 1-2 forces present is highlighting a possible issue anyway.

I am not 100% sure, but what happens if the PLC is re-started, either by power failure or Run-stop-run transition? Are the forces still present?

Should you not be looking at why the forces are happening in the 1st place? I am assuming that it is not you doing the forces?

We try to ensure that forces are only ever used for debugging, but never left in that state, too confusing for someone else to come along and work out.

IMO, it would be better practice to put in some commented code if a force needs to remain, at least that way, it is traceable and controllable..

 

[cjnichols]

lostcontrol

Thanks for your response comments below;

I would think that any processor that has more than 1-2 forces present is highlighting a possible issue anyway.

I agree fully in a system that is working fine there should be no forces at all.

I am not 100% sure, but what happens if the PLC is re-started, either by power failure or Run-stop-run transition? Are the forces still present?

The forces are removed but some of the sites that I have worked at had a list of all forces in a database and when something like this happened the force will be re-applied.

Should you not be looking at why the forces are happening in the 1st place? I am assuming that it is not you doing the forces?

You are right I am not the one doing the forcing there are other operations that have to use the system after it is installed and commissioned and we have no control over what they do.

We don’t care about if they force for an example an input for a minor process within the plant, but if they force an input that could cause major issues with the process of the plant that is when we want to stop the process.

We try to ensure that forces are only ever used for debugging, but never left in that state, too confusing for someone else to come along and work out.

IMO, it would be better practice to put in some commented code if a force needs to remain, at least that way, it is traceable and controllable..

I agree the more comments the better that everyone is able to understand what is going on.

Thanks


Chris