Programmer's mind? Multi Contact, multi Coil..

[CalG]

I persist with my efforts to "reverse engineer" the logic program for a vacuum process tool. This is a GE 90/30 application.

In study of the ladder logic , there are several instances where a single reference attached to a contact is used to control multiple coils, all on a single rung.

Then, in other sections of the program block, a single reference/contact is used to control multiple coil references, each on a separate rung.

What might be the "logic" to either of these approaches?

As I modify the program to add functionality of additional systems, I would like to understand the considerations and approach of the original programmer.

Your comments appreciated!

Cheers

Cal

 

[Lancie1]

...a single reference attached to a contact is used to control multiple coils, all on a single rung.

This is "parallel Outputs" where they all need to be switched on and off at the same time.

...a single reference/contact is used to control multiple coil references, each on a separate rung.

This case is usually when the coil outputs do not switch at the same time. Thye might go on at the same time but off at different times, or vice-versa. There should be some additional input logic that determines the differential control for the different coils.

On the other hand, I may have mis-understood what you are talking about. Two pictures would be worth 1000 words.

 

[CalG]

ascii graphics

Thank you for your response, I do not have the LM90 application on this Linux desk top, so screen prints are envolved, but this is what I am seeing in the ladder.


-]1M [--------------------------------------------------------(1Q)
-]1M [--------------------------------------------------------(2Q)
-]1M[---------------------------------------------------------(3Q)

vs

-]1M[--------------------------------------------------------(1Q)
L*---(2Q)
L*---(3Q)
*note "L"=vert link. For some reason, the spaces/tabs to the left do not carry through to the post. But these coils should be stacked on the right.

When 1M is true, 1Q, 2Q and 3Q are true,


At this moment, I do not see any difference in timing (certainly the first case the timing is not "exactly" simultaneous, but near enough for any purpose I can think of relative to event sequencing)



or I miss something

 

[ktmtragic]

No difference if 1M is the input in all cases. Just variations by the programmer

 

[kolyur]

There is no functional difference between the two scenarios you posted; it's just a matter of programming style. There should not be a timing difference either. With most PLCs, the output states are not updated until the end of the logic scan. Even if that weren't true, the difference would be on the order of microseconds.

 

[jrwb4gbm]

Here is a helpful hint that works for me. In your post #3, to preserve the spacing in ladder diagrams, do not "Preview" the post before posting (replying).

 

[Lancie1]

Yes, if the inputs on the left are the same, then there will be no difference in function or timing. Really, there is no reason to do the first case and split into 3 rungs, if all outputs are being controlled by the exact same device on the left. I thought there would be some difference on the left-hand side. Perhaps there was originally.

Warning: you really don't have a program that has two versions of the same 3 outputs (1Q, 2Q, and 3Q), do you? If so, only the last version would have any effect in most PLC programs. (I assume you just used those 3 as an example).

 

[CalG]

Lancie1

No duplications, just a quick example, references in the example are not taken from the ladder program.

But I did take a second look at the ladder listing. One thing noted is that in both cases all the coils are -(R)- resets.

a single reference %m0221 controls 128m.112m,116m,132m and 180m in sequential rungs. All are (R) references except 221m.

A different controlling reference is used on the same coil references in a different block.

The set coils for these same references are scattered in the ladder program.

Not sure if this means anything at all, hence my questions.

Thank you for your considerations

Cal

 

[jdbrandt]

I persist with my efforts to "reverse engineer" the logic program for a vacuum process tool. This is a GE 90/30 application.

In study of the ladder logic , there are several instances where a single reference attached to a contact is used to control multiple coils, all on a single rung.

Then, in other sections of the program block, a single reference/contact is used to control multiple coil references, each on a separate rung.

What might be the "logic" to either of these approaches?

As I modify the program to add functionality of additional systems, I would like to understand the considerations and approach of the original programmer.

Your comments appreciated!

Cheers

Cal

It may also be that the outputs are a different voltage than the inputs...or, are in remote locations.
In which case, there is no 'logic', per se, but the PLC is being used as a wiring multiplexer.

 

[CalG]

That may be true in cases

Jeffery

In this case, it's stuff like pneumatic valves, turning on / off additional electrical/electronic devices, starting timers etc.

 

[Mark-]

Hello,

A common occurance is the coils on each single line had other code at one time and it was removed. Easier/quicker to delete the unwanted code then delete all and replace.