Forces In Rslogix 5000

[Ron Beaufort]

so how much “force” does a “force” really have? ...

Greetings to all,

I’m still hoping that BobB will get back with us on that “Omron forces” question ... in the meantime, I’ve got a few extra minutes and so I’d like to comment on something that he said about the Omron forces:

Force a bit is force - brutal - effective - will stay that way until the force (or all forces) is cancelled. A bit can be forced on or off.

now I have no doubt that BobB knows exactly what he’s talking about with respect to the Omron system ... BUT ... just as a topic for further discussion for Allen-Bradley systems, the force is certainly not all that “brutal and effective” ... additionally, with an Allen-Bradley system, we can NOT say that “the force will stay that way until the force is cancelled” ... behold:

[attachment]

this little program demonstrates that an Allen-Bradley force is not nearly as “brutal” and “forceful” as we might assume ... here in rung #0001 a simple little OTE has obviously just kicked the force’s butt right out of the ring - and effectively overwritten the status of a “forced ON” input ...

as I said earlier, I have ZERO experience with Omron PLCs and so it wouldn’t surprise me at all if BobB’s test shows that their forces can NOT be easily overwritten like the Allen-Bradley’s ... but while we’re waiting for Bob to get back to us, I just thought that I’d throw some extra Allen-Bradley “force” trivia into the conversation ...

remember that BobB also made this statement:

Cannot comment on how this works with the above mentioned processors but would imagine in a similar vein.

obviously he correctly anticipated that there might be a few surprises when we start comparing how the “force” feature is applied from one brand of PLC to another ... this little demonstration is just one case in point ... party on ...

 

[RMA]

Oh boy, life gets ever more complicated, something else that I need to check out! However, this time I think I'm going to need help from Jesper or Paul to translate AB to Siemens, because I'm not sure I fully understand what's going on there, or if it's possible to program that sequence in S7. Being incompetent in ladder doesn't help, what would it look like in STL?

 

[fmadero]

Have you tried to inhibit the Rack? I did this and I could test just fine.

 

[daba]

Just to add a bit to Ron's execellent explanation...

In Allen-Bradley, the way output forces work make a difference for how seal-ins using an output address behave.

For instance, in a standard motor start-stop rung, if you seal in with the output address and then force the output off, the rung can still seal in. The result is that removing the force could cause the output to come on without a start button. As long as the start button was pressed sometime while the output was forced off.

I generally prefer to seal in with an input from the run contact for this reason.

And if that is not available, you can always make use of the readback tag from the output module....