Two OTE???

d21x · Aug 11, 2008

This might be a dumb question, but is it okay to use an OTE in two different places?

For example:

Rung 10 has OTE O:15/6
Rung 80 has OTE O:15/6

Reason I am doing this is because the original OTE rung has other outputs being energized, but I only want the one output to be energized. Please let me know if this makes sense? Thanks!

OkiePC · Aug 11, 2008

If this is a SLC, Micrologix or a PLC5 you are talking about, then RUNG 80 will solely determine the state of the actual output point (last rung wins since, after scanning logic, the data is sent to the output card).

It is a bad practice to use multiple OTE instructions with the same address. You should find a way to merge the logic so that all of the correct conditions turn on the output in one spot in the code.

robertmee · Aug 11, 2008

d21x said:
This might be a dumb question, but is it okay to use an OTE in two different places?

For example:

Rung 10 has OTE O:15/6
Rung 80 has OTE O:15/6

Reason I am doing this is because the original OTE rung has other outputs being energized, but I only want the one output to be energized. Please let me know if this makes sense? Thanks!

Bad idea...

To correct...

In Rung 10, replace OTE O:15/6 with OTE B3:0/0 (eg)
In Rung 80, replace OTE O:15/6 with OTE B3:0/1 (eg)

Make Rung 81 (XIC B3:0/1) || (XIC B3:0/0 * XIO B3:0/1)

|| = parallel branch
* = series

That will mimic what you have currently assuming that's the way you want it to operate.

d21x · Aug 11, 2008

Well, the way the program works is either Rung 10 will be on or Rung 80 will be on due to the conditioning before the OTE, not both. If I am thinking this way, would it still matter if i use the same address OTE in two different rungs? Not sure if this matters but its for a PLC5.

Otherwise I'll change the original OTE outputs to bits and have another rung for the OTE output.

OZEE · Aug 11, 2008

Yes, it will still matter. Even if Rung 10 is the only one that is "on", rung 80 is still being scanned and the output that will be active will be the result of rung 80 -- regardless of what happens in rung 10.

If you doubt this advice, just try it!

milldrone · Aug 11, 2008

OZEE, Robert, Paul,

I'm not an AB expert, but couldn't you put one OTE a subroutine and put the other OTE in another subroutine. Something like an "auto" sub routine and a "manual" subroutine. Only one subroutine could be active at a time. I know this works with GE

And unplug your telephone so you can get some sleep? I recognize it's still bad practice.

Tharon · Aug 11, 2008

Just some clarifications.

Outputs are only updated once per scan, and with what ever logical value they last had.

Don't forget the basics

Read Inputs.
Execute Program.
Write Outputs.

So at rung 10, it will "turn on" the output (but not really yet), but at rung 80, it will either "turn off" or "turn on". Then it reaches the end of the program and updates all the outputs. So the only one that really mattered was the last OTE executed, being Rung 80.

Of course, this sequence can be changed using other instructions, but that's not important right now.

allscott · Aug 11, 2008

The programming gods wil smack you down if you do this.

Not really but it is considered poor practice, the common way to handle this is what robertmee suggested. If one rung has the OTE energized and another has it denergized, the last one in the scan wins.

allscott · Aug 11, 2008

milldrone said:
OZEE, Robert, Paul,

I'm not an AB expert, but couldn't you put one OTE a subroutine and put the other OTE in another subroutine. Something like an "auto" sub routine and a "manual" subroutine. Only one subroutine could be active at a time. I know this works with GE

And unplug your telephone so you can get some sleep? I recognize it's still bad practice.

Yes this will work, I still don't like it though.

Steve Bailey · Aug 11, 2008

The fact that the original poster had to ask the question is reason enough to advise him against the idea. There are exceptions to just about every rule, but if you don't know why the rules exist in the first place, you're not ready to break them.

tomalbright · Aug 11, 2008

I'm really tempted to post a program I have had to maintain... It makes new light of this. Actually, look in topics. I'm gonna post it!

Craig Spinharney · Aug 11, 2008

Wouldn't recommend either.

I agree with what's been posted. I will sometimes program an OTU for that same output bit if the bit is being controlled by the OTE in a subroutine that I am no longer going to execute but want to reset.

Ken Moore · Aug 12, 2008

For the PLC-5's, I always have the ladder logic energize bits. Then I have a sub-routine called Outputs, in there all the bits are tied together to turn the outputs on or off as needed. It works well for trouble shooting later also. You have one place with all your outputs, and if you document fairly well, you know exactly what piece of code is controlling what output.

LJBMatt · Aug 12, 2008

d21x I agree with what everyone else has posted. what milldrone points out will work, but for anyone trying to debug or troubleshoot the program will turn into a nightmare rather quickly.

IMO the best thing to do for the easiest result would be to replace that output with 2 unique B bits and below rung 80 put those bits in parallel to turn on your output, which robertmee has pointed out.

Of course I "cringe" at the thought of 80+ rungs in a ladder but thats a philosophical debate for another thread.

Thomas · Aug 12, 2008

Only do this if you want to get a maintenance person fired for using excessive profanity and threats.

Two OTE???

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