Crazy question, I know....

showshocka

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Mar 2011
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510
hey guys, this i s a real crazy question. i just got finished designing a circuit with ice cube relays, now that i'm back in PLC ladder i'm a little confused. in this print, when OTE B:3 13/4 receives a 1 does it stay latched in from it's own XIC instruction becoming a 1?

question.jpg
 
from the "overkill" department ...

please understand that the following is written with absolutely NO OFFENSE intended ... but you've asked a question – I'll assume that you desire an answer ...

to get the "right" answer, we need to break your question down ...

when OTE B:3 13/4 receives a 1

actually an OTE instruction NEVER receives a ONE ... what you should have said was: "when the OTE instruction receives TRUE logic" ...

going further, when the OTE instruction receives TRUE logic, the processor will go and write a ONE into bit/box B3:13/4 ...

does it stay latched in

a better way to express this operation is that the rung remains "sealed in" ...

the term "latched" should (ideally) be reserved for the retentive instructions OTL (Output Latch) and OTU (Output Unlatch) ... the reason is that a truly "latched" rung will RETAIN its ON status after a "processor-go-to-run" event ... a "sealed-in" rung (like the one you've shown) will automatically be turned OFF each time the processor starts up ...

from it's own XIC instruction becoming a 1?

the XIC instruction doesn't "become a 1" ... a better way of expressing this would be to say: "since the XIC instruction for B3:13/4 will be evaluated as TRUE" ...

and getting down-right nit-picky about it (again, with no offense intended), you've used the wrong syntax for the address of bit/box B3:13/4 ... and furthermore, your use of "it's" as a possessive is grammatically incorrect ... "its" is the proper form of a possessive pronoun ... "it's" is actually a contraction – for the two words "it is" ...

now back to your original "crazy" question:

when OTE B:3 13/4 receives a 1 does it stay latched in from it's own XIC instruction becoming a 1?

suppose that you had phrased the question this way instead:

when the OTE receives TRUE logic, does the rung stay "sealed in" since the XIC instruction for B3:13/4 will be evaluated as TRUE?

I respectfully submit, with absolutely NO offense intended, that the only reason your original question was "crazy" (that's your word, not mine) is because you do not know exactly how your Allen-Bradley processor operates "under the hood" ... trust me, you are NOT alone in that situation ...

so ... finally ...

the answer to the properly phrased question would be:

yes, the rung will stay sealed-in – until/unless something writes a ZERO into bit/box B3:13/4 ... or ... until the processor has a "go to run" event – in which case PRE-SCAN would execute the OTE instruction – and cause the processor to go write a ZERO into bit/box B3:13/4 – and so the rung would lose its "sealed-in" condition ...
 
In the study of Boolean logic, a "1" is often referred to as TRUE and a "0" is FALSE. In the Boolean world, the two concepts are equavalent, so I think we all know what Showshocka meant. In many spreadsheets, if you look at the value of Boolean logical TRUE, you can see that it is "1".

If you really want to get technical, internal to the PLC, both 0 and 1 are really voltage level ranges, Logic 0 is not exactly 0 volts, and Logic 1 is hardly ever 1 volt. The definition of logical 0 and 1 varies, so it does help to know the definition for the device you are working with.
 
Greetings Lancie1 ...

so I think we all know what Showshocka meant.

yes, you're correct ... and I assure you that I did indeed know EXACTLY what he meant ... I hear the same types of questions (often word-for-word) day in and day out ...

and ...

THAT is precisely the reason that I answered the question the way I did ...

specifically, because the OP – and many other readers - are confused by the ladder logic used in PLCs ... the reason for much (MOST?) of the confusion is the terminology that gets used (actually MISused) in teaching the basic concepts ...
 
please understand that the following is written with absolutely NO OFFENSE intended ... but you've asked a question – I'll assume that you desire an answer ...

to get the "right" answer, we need to break your question down ...



actually an OTE instruction NEVER receives a ONE ... what you should have said was: "when the OTE instruction receives TRUE logic" ...

going further, when the OTE instruction receives TRUE logic, the processor will go and write a ONE into bit/box B3:13/4 ...



a better way to express this operation is that the rung remains "sealed in" ...

the term "latched" should (ideally) be reserved for the retentive instructions OTL (Output Latch) and OTU (Output Unlatch) ... the reason is that a truly "latched" rung will RETAIN its ON status after a "processor-go-to-run" event ... a "sealed-in" rung (like the one you've shown) will automatically be turned OFF each time the processor starts up ...



the XIC instruction doesn't "become a 1" ... a better way of expressing this would be to say: "since the XIC instruction for B3:13/4 will be evaluated as TRUE" ...

and getting down-right nit-picky about it (again, with no offense intended), you've used the wrong syntax for the address of bit/box B3:13/4 ... and furthermore, your use of "it's" as a possessive is grammatically incorrect ... "its" is the proper form of a possessive pronoun ... "it's" is actually a contraction – for the two words "it is" ...

now back to your original "crazy" question:



suppose that you had phrased the question this way instead:



I respectfully submit, with absolutely NO offense intended, that the only reason your original question was "crazy" (that's your word, not mine) is because you do not know exactly how your Allen-Bradley processor operates "under the hood" ... trust me, you are NOT alone in that situation ...

so ... finally ...

the answer to the properly phrased question would be:

yes, the rung will stay sealed-in – until/unless something writes a ZERO into bit/box B3:13/4 ... or ... until the processor has a "go to run" event – in which case PRE-SCAN would execute the OTE instruction – and cause the processor to go write a ZERO into bit/box B3:13/4 – and so the rung would lose its "sealed-in" condition ...

WOW! You really gave it to me. With all due respect, that was a little discouraging from coming back for help. Is that not the reason why I'm here, to ask question's at "Live PLC Q&A"? Not trying to be sarcastic but that was really motivating, really, it was. With my use of "it's" is the product of typing on the fly with a lot of other things going on at work. Maybe I am totally lost.... No offense taking but once again but WOW. I hope you will still help me in future post.:geek:
 
Easy SS!! I assure you that Ron is the last one who would be condescending to anyone. What he WILL do is thoroughly explain to you in layman terms what you need to be proficient at these PLC things. He wasn't talking down to you and never will.

I think you might have misread his intent but don't misread his posts. They're gems in a world of coal.
 
I find this a bit too 'nit-picky'; it's in text, does not affect the understandability of the question and does not demonstrate a basic misunderstanding of the addressing. It's correct in the ladder.

and getting down-right nit-picky about it (again, with no offense intended), you've used the wrong syntax for the address of bit/box B3:13/4 ...

And this I find not needed at all. I'm sure most of us are good enough readers to skim over normal misspellings without coming to a screeching halt.

and furthermore, your use of "it's" as a possessive is grammatically incorrect ... "its" is the proper form of a possessive pronoun ... "it's" is actually a contraction – for the two words "it is" ...
 
all things must come to an end ...

I apologize ...

somehow I misunderstood ... I "THOUGHT" that the OP was asking for help ... I offered the best that I had ... apparently I offered too much ...

I can assure you that it will not happen again ...

so ...

it's been fun – but it's been done ...

I wish you all the best ...
 
I apologize ...

somehow I misunderstood ... I "THOUGHT" that the OP was asking for help ... I offered the best that I had ... apparently I offered too much ...

I can assure you that it will not happen again ...

so ...

it's been fun – but it's been done ...

I wish you all the best ...

I really hope that's not the case...
 
Ron, your posts and your schooling are treasured. But if a minor questioning of your post, which was a lengthy response to a two-sentence question, causes such a reaction then something is up. By the way, and no offense intended, you missed that his sentences didn't begin with a capital letter.
 
Ron:

As always your answers are appreciated. If Showshocka doesn't appreciate them, then it is his loss.

Showshocka:

Look at the number of Ron's Posts, almost all helping people, and look at your Posts, almost all asking for help over and over.

Perhaps you should rethink your response.

Stu....
 

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