New to AB Ladder, is there inline NOT?

[CapinWinky]

I have some logic that is way easier to understand if I put in when I don't want an output to turn on, but I can't seem to find a boolean NOT or even a normally closed output to use with this inverse logic. The NOT instruction that does exist takes an input and output variable, it isn't an inline NOT.

It currently looks like the only way to do this is to make two rungs. One way is to set a flag with the logic in one rung and in the second use that flag with an XIO. I could also have a rung that latches the output and a second that unlatches it according to my logic. That can't be the only way to do this, but I looked through the available instructions and nothing jumped out as being able to do this cleanly in one rung.

 

[harryting]

I am having problem understanding what you are trying to do. XIO is boolean NOT, well, pretty close. It MAY makes thing clear with a second flag that's the inverse but it's not necessary.

So if you have bit, X and you want the inverse.

IF NOT(X) THEN...

is the same as

---XIO X------( ... )---

 

[gbradley]

Would an Unlatch work?

 

[geniusintraining]

...One way is to set a flag with the logic in one rung and in the second use that flag with an XIO...

I'm OK with this... I have done it and seen it done a lot

 

[nwboson]

I had used Allen Bradley for years, then did a project in Siemens and ran across their inline NOT. I loved it - take a slew of boolean conditions, then invert the whole sense of the expression.

Allen Bradley does not have an inline NOT and I do miss it when I do an AB program: without the inline NOT, for complex expressions it sure helps to know your DeMorgan.

 

[CapinWinky]

An example of what I want:
--] A [--] B [--|-----[NOT]-----(Output)
--] D [--] C [--|

Which is an easier to follow way of doing this:
--] /A [--|--] /C [--|-----------(Output)
--] /B [--|--] /D [--|

 

[CapinWinky]

Well, I guess I'll stick with using an intermediate flag. It's pretty silly that AB doesn't have either an inline NOT or a normally closed output.

 

[TConnolly]

The PLC/5 has one. The INV instruction inverts the rung state. I found it to be a very handy instruction in certain situations. For whatever reason, AB chose not to extend that instruction to the SLC and ControlLogix Ladder languages, but NOT is available in FB and ST languages.

 

[harryting]

Oh, I see. I don't remember much about the PLC5 days but I feel that's even more difficult to read to me.

Now if you want to talk about how AD handles numerical operations...

 

[Temper]

I did that once. Millwrights replaced a valve and either they installed it backwards or the wrong valve, but it was activated down instead of up. I just edited the output to a bit and the next line examined if the bit was off to fire the output. Worked fine.

 

[devo.xx]

It currently looks like the only way to do this is to make two rungs. One way is to set a flag with the logic in one rung and in the second use that flag with an XIO.

Yep.
Same thing with Rising and Falling pulses, they don't have an inline argument for a rising Bit, nor a rising Rung...
They have the inline NOT for FB and ST as TConnolly mentioned.

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