slc5/05 forces

Please help as I have called AB Techconnect with no help at all.

I have slc 5/05.
One card is an ob16. I have output 01 forced on. Forces are enabled.
I have another output card that has outputs forced off. These work fine.
The ob16 output 01. Actually follows the program logic. Off when expected and on when expected. But still shows (ON) in red. The true output is changing it will not stay forced on.
Has anyone ever seen a force not work?

You don't have a master relay instruction above dropping it out do you? I have seen this before.
LR

Greetings Randy ...

and welcome to the forum ...

by "true output" are you referring to the OTE on the screen - or to the actual device located in the field? ...

secret handshake: a "force" on an output (specifically, something with an O:___ address) does NOT (I repeat NOT) affect the status of the bit on the output image table ... so if you're expecting the force to make the OTE instruction turn green on the screen - that won't happen ... on the other hand, the actual device located in the field SHOULD turn off or on as dictated by the enabled force operation ...

you might want to take a look at Email Quizzes #115 and #215 (see the Sample Lessons page) on my website ... the answers go into quite a bit of detail on this type of material ...

Forcing in the SLC 500 and all other PLC types can be dangerous if you don't understand how that PLC uses forces. How does forcing in THAT PLC affect your physical and logical outputs. You should NEVER force if you don't understand the function. Rockwell holds hundreds of classes a year, including a Maintenance & Troubleshooting class.

That said, I will step off my soap box. Forcing an output in the SLC 500 only affects the PHYSICAL output. You will see the "ON" and "OFF" text appear below the addresses in the logic but other than that, you will see no other result from forcing in the logic.

If the ladder logic says, turn the output off, then the output will appear off in the logic, but if it is forced on, then the PHYSICAL output will turn on but NOT the one in the logic. The logic will show you the "logical" state.

Think of it like a jumper wire. If you went out to the output module and placed a jumper wire on the output terminal puttng voltage on the terminal would you expect to see the output energized in logic?

As to the TechConnect contract being no help. I'm curious what you mean by that. This is a question they can easily answer.

OG

Thanks for the input.

The device the output was connected to was changing state. That is the valve would actually energize and de-enegize just as if the force was not istalled. The led indictator would change and the logic would change.

This may be one of those things that will remain "That can't happen."

Debug is over so the forces are removed, hopefully I can recreate the problem on the bench but who has time for problems that are not direct productuion issues.

If anyone would like to try this I would still like to know why. This was the logic and results. i/o names simplified.

-----[]--------------[]---------------()
i;0 o;0 o;1

with no forces

i;0 o;0 o;1 valve @ o;0 valve @ o;1
0 0 0 0 0
0 1 0 1 0
1 0 0 0 0
1 1 1 1 1

with o;0 forced on
i;0 o;0 o;1 valve @ o;0 valve @ o;1
0 0(1) 0 0 0
0 1(1) 0 1 0
1 0(1) 0 0 0
1 1(1) 1 1 1

As you see the valve at o;0 did not respond as expected when forced on. The valve should have been energized at all times.

By say AB was no help I simply meant they said the same as me. This should work fine there are no known issues with he force command.

You forced it on... did you ENABLE the forces? It's a two-step process on the SLC500.

...it's just a question, maybe "obvious", lol...

Have you tried installing a different output module in the slot that is giving you trouble? See if anything changes.

Just a thought.

Forces were installed and enabled, there were other forces being used that worked fine.

1st thing I tried was an output card.

Sorry my truth table did not come out the same for you as it did when I made it.

I would have to say operator error. I expanded your truth table, and there's no reason that the valve attached to O;0 would have continued to cycle. So, my guess would be:

You forced ON the wrong output
or
The valve you were checking is not actually wired to O;0.

I'm still not 100% clear on the situation.

For the truth table you gave, O:0 is the only force?
O:1 and the device connected to it went off and on as described?
That's normal, a XIC with address O:0 is not affected by the force status, only the logic status.

The device connected to O:0 went on and off according to the table?
Now that's weird. The device connected to O:0 should be on all the time if it O:0 is forced ON. It's logic status can go on and off and change the state of O:1, but the device connected to O:0 should be on.

That is not the case. I am only using 1 (one) output on that entire card. The machine is in operation and the forces were removed after debug now it works great.