RSL5000 Coils in the middle?

DairyBoy

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Hi all. Gettin' ambitious now :whistle:

I'm trying to extract the status of the limit comparators (only) without half-duplicating the rung. When a limit comparator output is true, will the associated B2.n coil be enabled without affecting the final B21.n coil or will the B2.n coil pass logical continuity on to the B21.n coil irrespective of the state of the second comparator? Thanks.
 
First rung, 4 branches each with LIM instructions out to B2.x

Second rung, 4 branches each with B2.x contact in series with comparative box, then out to B1.21.

A net addition of 4 contacts and more readable.
 
I didn't think the rung would be accepted but it was. I really don't know. If the first output passes its TRUE state then the paralled comparison is nullified. I've never put an output except as a rightmost column entry.

I'll add, if the rung isn't obvious then break it up. Rungs are cheap.
 
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Unfortunately RSLogix5000 allows for more then one output instruction on a rung.

The GEQ and LES instruction on the first rung serves no purpose. If the limit instruction is true then both outputs will also be true.
 
That rung will indeed work in Logix5000. However It will be a lot more readable and understandable if you program it as five separate rungs. The extra rungs won't be any more overhead than the branches and it eliminates the "WTF!" factor from your program.
 
It started life as expressions in the PV+ "visibility" fields but it ended up reading like a novel! Hence the migration to the plc.
 
I acutally think the rung looks just fine except for the fact that the LESs and GEQs do nothing.

DairyBoy said:
. . . But does the pdf version work as I expected?
Click to expand...

Not if I understood the original post.

EDIT: Try it like this:

Branched_series_OTE.png
 
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So a B2.n will be set by the LIM function without the need for subsequent logical continuity via the associated comparator?
 
DairyBoy said:
So a B2.n will be set by the LIM function ...?
Click to expand...

Yes. The subsequent comparators will still determine the state of that last OTE instruction...do you still need it to work that way? I was under the impression you simply added branched OTEs to a rung that was already doing what you wanted for B1.21

To clarify, when true, the OTE instruction will pass logical continuity on to the next instruction to the right.
 
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So a B2.n will be set by the LIM function without the need for subsequent logical continuity via the associated comparator?
Click to expand...
huh? ...

I'm just guessing at what you mean – but ...

if the "rung condition in" to an OTE is TRUE, then the OTE will "go write a ONE" into its bit/box ... specifically, you do NOT need "continuity" AFTER the OTE in order for the OTE to work ...

in simplest terms, the rung is NOT really an electrical circuit that needs a "return path" in order for logic/current to flow ...

does that help – or hurt? ...

 
Ron Beaufort said:
does that help – or hurt? ...
Click to expand...


Yep, the coils in RSLogix5 and 500 were single voltage coils...one per branch or they would burn up. The new hi-tech coils in RSLogix5000 are of the infinitely variable voltage type so you can put them in series or parallel...
:)
 
It's ok, Ron. I'm aware of the risks when taking an analogy too far but the idea of coils being accepted in that position, let alone doing something (hence the question about their behaviour) is new to me so I was still angling for an answer to the questions: Do they turn on and off as though they were the last item on the right? Will a set coil in parallel with say, a comparator bypass that comparator's effect on the rung? My favourite so far is OkiePC's; quirky, but so is 5000. Edit: Just read OkiePC's "constant-current" example. Quick, Ron: Call the Analogy Police!!! ...and anyway, I did say logical continuity; wasn't that the original idea behind ladder logic?
 
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Adding to what Ron points out, ladder logic is a representation of logic which makes an analogy to electrical ladder wiring diagrams. But merely being an analogy it may or may not EXACTLY follow electrical methods. RSLogix 500 enforced a 'coils in the right column only' scenario while RSLogix 5000 chooses to allow multiple output symbols in series.

But, being that they still will be read by those with a more electrical understanding, I will choose to use a 'coils at the right hand side' restriction and use parallel branches when multiple outputs are to be energised. And it just reads more naturally to me. Maybe I'm just old.
 
I hear a LOT of misconceptions in my line of work ...

I've actually had students in my classes (some with several years of experience) who have pointed out that a PLC can't use a 120 VAC input (a switch in the field) to control a 24 VDC lamp in the field ...

the reason? ...

the 24 volt lamp bulb will "blow out" when the 120 volts from the switch flows through the rung ...

for many years now, people have been trying to "water down" ladder logic to make it digestible for "mere electricians" – and there are some really weird misconceptions floating around out there ...

we need to remember that there are a lot of other people reading over our shoulders as we write this – and this thread will be here for many years to come ... so while WE might perfectly understand what's going on, we really should make things as unambiguous as possible for those who'll pass this way in the future ...

party on ...
 
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