New to PLCs - Ladder branch question.

I installed ControlLogix from AB. I need to learn PLCs for a better job. My first test project is to simulate the controls on my home furnace. This will be on the PC only.

The split rung is needed for the NO low water temp and NC high water temp to act as a seal to keep the output on (burner) until the high temp switch opens. I also wanted the burner to go on when the house t-stat calls for heat and the high temp switch has not been reached. Lastly I wanted a over temp switch to start the circulator pump in the event of extreme over temp to prevent boil over.

I can not seem to get the rung to start after a XIC and perform an output with out joining back to the rung it started on.

Any help would be most welcome. Thanks!

First, it is based to name your inputs based on the condition which causes the input to turn ON.

List each of your inputs. What condition is detected by an ON condition?

In terms of the now properly named inputs define the logic for the burner and for the circulator pump. Each can be their own rung, one terminating in the 'burner on' output, the other in the 'pump on' output.

Then we'll worry about drawing that using the rung editor in ControlLogix.

Greetings Factory guy ...

regarding:

I installed ControlLogix from AB.

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no offense, but you probably meant to say: "I installed RSLogix5000 from AB" ... ControlLogix is physical "hardware" ... on the other hand, RSLogix5000 is the "software" package that is used to program the ControlLogix hardware system ...

My first test project is to simulate the controls on my home furnace. This will be on the PC only.

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do you understand that if ALL you have available is RSLogix5000 loaded on your computer then you will not be able to "run" the program that you're writing – and so you won't be able to test its operation ... specifically, in order to run the program that you write, you'll need something else such as an "emulator" (additional software) or some type of physical hardware ... neither of these is likely to be "free" – as long as you stay with RSLogix5000 ...

just a suggestion: if this is your first experience with PLCs, you might want to consider downloading the free 15-day trial software at www.thelearningpit.com ... (I have no relationship, financial or otherwise, with that site) ... the best thing about going that way, at least in the beginning, is that you'll be able to test whatever you write ... many (most?) beginners start out that way ...

or ... tell us more about what resources (hardware, software, etc.) that you have available and we'll be glad to help you put something together that will help you along the way ...

we wish you the greatest success in your project ... and welcome to the forum ...

Yes I have the trial software and no real hardware, so I will not be able to provide an actual address for any firmware. My project is based on my oil furnace operation. It has an oil burner, water pump, low water temp switch (N.O.) and a high water temp switch (N.C.) The low temp starts the burner, then the high temp shuts it off. The burner can also be started when the t-stat calls for heat, provided the high temp switch has not kicked in (it opens at the set temp).

My inputs are 1. a home t-stat that closes when calling for heat. 2. a N.O low temp switch that closes when the burner should lite. 3. a N.C. high temp switch that opens when the burner should be shut off.

My outputs are 1. a oil burner, and 2. the water pump. I would like to latch the high/low and use the t-stat as a low temp trigger so the burner kicks on when the circulator pump dose.

I watched all the intro to the software. It is RSLogix 5000

Thank you.

Here is how I would approach any project. (Thanks to Ron for pointing out the major tip step 1 and for inspiration for my post.)

1. Define the inputs and outputs. As Ron said, use positive logic descriptions. For example if the home t-stat closes when calling for heat, define it as I_Tstat_Heat_Request or something as meaningful. I always use I_ and Q_ prefixes for discrete I-O tags so they are easy to spot in the program. For your oil burner I would choose Q_OilBurner_On.

2. With the I-O defined you then select hardware that will accomplish the project needs. This can be as simple as whatever is the cheapest solution to as complicated as customer specific requests for software/hardware.

3. At this point you have the I-O defined as well as the hardware platform which dictates the software platform. You are ready to program. At this point I don't program - I write a detailed sequence of operation. If you can say it - you can program it. This also gives you something to present to the customer and say: This is how I understand you want it to function - please speak now or forever hold your peace. That last bit usually is never stated, you understand.

4. With an agreed upon sequence of operation it all gets very simple. You just make the PLC program do what you agreed it would do. I find at this point the program pretty much writes itself since you have already worked out how it works in the sequence.

Factory guy said:

I can not seem to get the rung to start after a XIC and perform an output with out joining back to the rung it started on.

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If I understand you correctly, you seem to be confused by the fact that a branch begins and ends on the main rung line. This is normal. Just add your instructions to the branch.

You may also want to take a look at this post: http://www.plctalk.net/qanda/showpost.php?p=296358&postcount=4

And welcome to the forum.

so I will not be able to provide an actual address for any firmware.

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well, yes you WILL be able to provide addresses – because you can just insert "make believe" modules into the I/O Configuration area and then you'll be able to use the resulting addresses in your program ... (and no offense but the word "firmware" doesn't really fit in the statement that you made) ...

but ...

somehow I still don’t think that you fully understood the thrust of my earlier post ... the main idea is that WHATEVER program you write, it will only be a static "picture" of rungs and instructions on the computer screen ... specifically, you will NOT be able to see it "run" or "light up" or "execute" or "do anything" ... now if that's OK with you, then it's OK with us ... it's just that you're only going to be able to go "so far" up the learning curve – and it won't be nearly enough to meet your stated goals ...

disclaimer: I'm basing this on what you've posted so far ... you still haven't told us exactly what resources that you have available ... I'm assuming (gosh I hate that word) that you ONLY have RSLogix5000 loaded on your computer – and NOTHING else ...

important: please do NOT let anything I'm saying discourage you in any way ... that is NOT my intention ... it's just that we see a LOT of enthusiastic beginners around here who quickly drop by the wayside ... usually it's because they don't fully understand what it takes to put one of these "train sets" together – and so they often get discouraged and give up because nothing seems to work properly ... we can help with those types of problems, but you've got to tell us what sort of toys you have available to play with ... the more you tell us, the more detailed help we can offer ...

again, good luck with your project ...

finally a note to Paul B ... my distinguished colleague Bernie should get the credit for the excellent "how to list the I/O" tip ... I'm still stuck back in the starting gate worrying about how Factory Guy is going to learn anything really useful without being able to "test run" whatever program he eventually writes ... at this point I'm still afraid that he's washing and waxing a brand new car – that doesn't have an engine in it ... that's probably going to be very disappointing when he finally turns the key to take a drive around the block ...

then again – maybe I'm wrong ... that's happened before ...

Ron said:

well, yes you WILL be able to provide addresses – because you can just insert "make believe" modules into the I/O Configuration area and then you'll be able to use the resulting addresses in your program

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With the PLC (and RSL5000), just use some bit addresses as you need them, using "fake" IO, without a real input or output address. It's easy to check your logic without troubling your real world outputs or family. Toggle your bits for a while. You can always assign an alias to IO later when you are happy with what you have programmed.

I love ControlLogix/RS5000.

well, I'll admit that it's good advice - but it doesn't quite "fit" ...

Greetings tomalbright ...

no offense intended, but let's take Factory Guy's statement (below) at face value ...

Yes I have the trial software and no real hardware, so I will not be able to provide an actual address for any firmware.

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based on that "no real hardware" part, I've got a hunch that he might just become slightly confused by the advice that you've given him ...

It's easy to check your logic without troubling your real world outputs or family. Toggle your bits for a while.

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yes, he can certainly toggle the bits – but unfortunately it really is NOT going to be "easy to check his logic" because his program isn't going to execute and actually "do" anything ... notice that he (apparently) doesn't have access to either an "emulator" software package – or to a real processor ... (I'm betting that you simply missed that fact in the earlier posts – and so based on that, the advice that you offered was excellent – but it just doesn't fit the situation at hand) ...

With the PLC (and RSL5000), just use some bit addresses as you need them, using "fake" IO, without a real input or output address.

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again, this is excellent advice – but as far as I've been able to tell so far, Factory Guy doesn't HAVE access to a PLC ... let's consider that one thing that he does need to start learning about is how to decode ControlLogix addresses such as "Local:1:I.Data.0" and so forth ... I'm thinking that he'll stand a far better chance of learning that sort of stuff by inserting (imaginary) I/O modules into the I/O Configuration feature ... he can't do a LOT without a processor – but at least he can do THAT much ...

the reason that I'm taking such an interest in Factory Guy's problem is that nowadays I'm getting about three or four calls a week from folks who are in exactly the same boat that he's in ... they're all trying (bless their hearts) to learn as much about PLCs as they can with very limited resources ... I'm offering our original poster the same type of free, friendly advice that I routinely give out over the phone ...

I still stand by my original statement that it would be much more educational for these "low budget" beginners (no offense intended) to cut their teeth on the free exercises available from The Learning Pit – because at least there they can get instant feedback on whether their logic programs are working correctly or not ... once they've worked their way through that material, then (and ONLY then) would it be appropriate to move on to some type of (non-free) real-world hardware ...

anyway ... that's the best advice that I personally have to offer – and I'm sticking to it ...

(again, I have no connection, financial or otherwise, with The Learning Pit) ...

party on ...

[shameless plug]
Don't forget about the PLC simulator offered by the host of these forums.
[/shameless plug]

http://www.plcsimulator.net/

Its not as sophisticated as a full blown simulator, but its a good place to start.

I don't want to distract from the original processor software for ControlLogix. Since the ability to simulate has been mentioned in the original post, here is a link that discusses a processor that has simulation mode in the programming software.
Link:
http://www.plctalk.net/qanda/showthread.php?t=50078&highlight=pico

I didn't miss the original lack of PLC, just offering a suggestion... he will no doubt buy a PLC to try his logic out, and that's food for thought. However, you are correct, no simulator, no means of trying the logic NOW is a problem to deal with.

He mentioned not having IO - that's not a problem with ControlLogix. I assumed he was having difficulty assigning real world IO. At this stage, that doesn't matter.