Forcing bits

realolman

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Control logix5000. If have an XIC on a rung with an OTE I can force the OTE on but if I force the XIC it doesn't turn on the OTE. Why is that? Am I missing something? Thanks
 
I am sure this has been posted before on here but Logix5000 will only allow forcing of real I/O so if your XIC is not a real I/O then it will not allow you to force it on.
 
just a guess - based on what you've posted, it sounds like the rung is not being scanned ...

going further ...

note that in Allen-Bradley you do not force BIT/BOXES ... instead:

(A) in the case of an INput you force the signal coming IN to the bit/box (so the bit/box DOES change state) ...

on the other hand ...

(B) in the case of an OUTput you force the signal going OUT of the bit/box (so the bit/box does NOT change state) ...

and incidentally, the little popup Tool Tips for the outputs are wrong ... ignore those for best results ...

if this doesn't nail it down, consider posting a screen shot ... some of what you're saying doesn't quite add up ...
 
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Hi

You also have to enable all forces with the drop down box beside the remote run drop down box.

Are you forcing a output or a plc bool bit


Donnchadh
 
It depends...

If you are forcing an input address, it should work and the XIC should reflect the forced state.

However, if you are forcing an output address, the XIC will reflect the state of the program logic and not the forced state.

It's important to note that you are not forcing the XIC. You are forcing an I/O point.

The way I think of it is:
Output forces are applied between the output address and the actual I/O point. Therefore a force does not affect the output address state, just the hardware.
Input forces are applied between the actual I/O and the input address. Therefore they DO affect the input address state.

Hope that helps.

Edit:
As usual, Ron covered the same concept and did a nice job of it. Perhaps my slightly different wording will be helpful.
 
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There's more to it than I posted but the gist of what I posted is correct
A rung with an XIC and an OTE. I highlight the XIC and force it on and it shows "ON" but it does not turn on the OTE that follows
If I force on the OTE it actually does turn on. Seems to me it would be
Useful to be able to "true" an XIC and have it do what it would do if it were "trued" during normal operation... In this case turn on the OTE.... But apparently that doesn't work
Seems that it ought to
 
If I force on the OTE it actually does turn on.
Click to expand...
we're just not understanding each other here ...

what do you mean by saying that the OTE actually does "turn on" ? ... do you mean that it turns green on the screen? ...

that usually does NOT happen when you "force" (as you're saying) an OTE ...

secret handshake: OTEs are INSTRUCTIONS – they do not "turn on" ... all that they EVER do is tell the processor to either:

(A) "go write a ONE into a bit/box" ... or ...
(B) "go write a ZERO into a bit/box" ...

more specifically, an OTE is NOT an "output" – it is NOT a "bit" ... you can NOT "force" an OTE ... instead you force the output signal that goes from the output bit/box to the output module ... (see what mellis said in an earlier post) ...

just guessing here – taking your statement at face value, the only way that what you said makes sense, is for the OTE to be referenced to an INPUT address ... for example: an OTE addressed to Local:1:I.Data.0 would turn "green on the screen" ... is that what you're doing – and seeing? ...

note that the address mentioned above is an INPUT address – regardless of the fact that it might be referenced to an OTE instruction ...

sorry – but without a screen shot it's really pretty hard for us to give you more than guesses ... we're not trying to be difficult here – and we're really trying to help – but we need more to go on ...

.




forcing_ins_and_outs.PNG
 
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The bit is NOT an input

Bit ...............Solenoid
----| |-------------( )----

Bit ............. ..Solenoid
----| |-------------( )---- Solenoid output NOT energized
ON

Bit ................Solenoid
----| |-------------( )---- Solenoid output energized
...................ON

Bit ................ Solenoid
----| |-------------( )---- Why doesn't this happen?.
ON

Seems to me this would be more useful than the way it DOES work
 
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Here's something you learn well in Ron's class:

"Is something else controlling the bit?" Is there another instruction somewhere else in the program that is telling 'solenoid' to have a zero in its bit box?
 
There is a similar way to test your logic, I never liked forcing as I almost always forget to put the logic back to normal,
Create a Dint array in your Controller tags I usually call It my initials_bypass or _test
use these as a wrap around the bit you want to force and simply use the Ctrl T to Toggle ON and then Ctrl T again to Toggle Off
I like this because when you are finished testing you can do a quick monitor of this array to see if anything is left ON
 
Mark Snodgrass said:
Here's something you learn well in Ron's class:

"Is something else controlling the bit?" Is there another instruction somewhere else in the program that is telling 'solenoid' to have a zero in its bit box?
Click to expand...

So you're saying if this was the only run in the logic that forcing the bit on would true the OTE? But there could be another rung turning it right bAck off?
That's entirely possible. Bet that's what's goin on. Thanks all
 
looks like Mark has given you something to work on ... here are some other notes that might be helpful ...

I think that what's confusing this discussion is that you seem to be assuming that the OTE is "green on the screen" when the Solenoid device in the field is being forced ON ... take another look ... I've got a hunch that you'll see something like the action shown in the figure below ... this is taken from my Email Quiz "Beginner Level #115 – Toggling and Forcing" available by following the link from the "Sample Lessons & Videos" page of my website ... (no registration is required) ...

.

figure_5.jpg
 
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