Errors in Ladder program

Hello, I've been struggling to find out what is wrong with the attached program, but i'm not sure of my answer. Please help me find our the errors in the program.
My approach:
-I think there is an addressing problem i can't figure out
-The negated contact 1.02 could also be a possible problem

As you see i'm not sure of myself...

You need to provide A LOT more information than what you have.

How is anyone supposed to help you without knowing what you are trying to achieve?

There are no IO or rung comments, or description of what is the purpose of the code?

The negated contact 1.02 could also be a possible problem

Click to expand...

Could be, but then it depends on what its function is, but it is pointless having it as the 2nd contact, IMO.

The 0.00 rung segment has no effect on the outcome of the rung. The NC 1.02 disables the entire rung when 1.02 becomes true.

lostcontrol said:

You need to provide A LOT more information than what you have.

How is anyone supposed to help you without knowing what you are trying to achieve?

There are no IO or rung comments, or description of what is the purpose of the code?


Could be, but then it depends on what its function is, but it is pointless having it as the 2nd contact, IMO.

Click to expand...

The only thing i'm trying to achieve is a better understanding of ladder logic in preparation for an exam. This is simply a sample exam question.

what is wrong with the attached program?

Click to expand...

Is that the test question?

So we have at least two answers:

1. No Comments

2. Superfluous contacts

Thanks for your suggestions.
The exact test question is:

What is wrong with the attached program?

Nothing really wrong, it probably does what it's supposed to do. In any case, I'd have a closer look at the (NC O.00 AND NO 1.02) branch, as it seems to be redundant because of the NC 1.02.

The problem is that it's YOUR homework. We don't do YOUR homework for you.



What do you suspect the problem is?

What is the rest of the program? One rung does NOT make a program?

What is the context of that rung? It does exactly what it's programmed to do -- and we have no idea of its intent.

OZEE said:

The problem is that it's YOUR homework. We don't do YOUR homework for you.



What do you suspect the problem is?

What is the rest of the program? One rung does NOT make a program?

What is the context of that rung? It does exactly what it's programmed to do -- and we have no idea of its intent.

Click to expand...

I'm asking because i'm still learning, and i included my ideas in my original request:

" My approach:
-I think there is an addressing problem i can't figure out
-The negated contact 1.02 could also be a possible problem

As you see i'm not sure of myself... "

The biggest problem with the rung is that, without any context, it doesn't provide enough information to answer the question. That's saying essentially the same thing that Bernie noted in his first point. We don't know if the addresses assigned to the contacts represent inputs, outputs, or internals. We don't know what states or conditions they represent. Is the coil instruction addressed to a real-word output or an internal?

Without that context, about the only thing you can say is what you've already identified. The usage of address 1.02 looks a little suspect. The rung might do what it's supposed to or it might not, but the way it's constructed is awkward.

If you've been given this rung and nothing else and the question is "what's wrong with this rung", then best answer is probably "lack of documentation". If you do have more information about the system this rung is part of, then share that with us and maybe we can help you find a better answer.

I guess it depends on how you define "error"

That 1.02 won't fault the processor. It's just careless programming, perhaps even the result of a typo.

0.07 will still be triggered by the bottom branch.

But one rung out of context with no documentation still means absolutely nothing.