help debugging Micrologix program

[milldrone]

Sparhawk,

This is the "Ron" robertmee is referring to. http://www.plctalk.net/qanda/showpost.php?p=303526&postcount=26

My comment about Ron is that he LOVES these discussions and has contributed to them at length over the years.

The one I linked to, was last week. Here are some more.
http://www.plctalk.net/qanda/showthread.php?t=33986&highlight=latch
http://www.plctalk.net/qanda/showthread.php?t=25873&highlight=latch

Does Ron not like these discussions? I don't know him, no biggie.

Like many of us, Ron has a self professed addiction to this site, so his solution is to not have internet access at home. He may showup on Monday although.

Oh! And welcome to the forum!

 

[dahnuguy]

a few thoughts

ROn is smart for not having the net at home.

I must begin with my recent thought change.

In the real world of physical relays, a latch will hold the output true with itself. So it is constantly re iterating the on condition. This is necessary due the "return to open" spring function in the relay. I have used relays that have 2 coils and they do not return . They are voltage to open and voltage to close. Bistable.

Now to my recent change in thought.

For some reason I had always considered a OTL to be a real latch but in reality it is like a dual coil relay. OTL to close OTU to open.

The OTE closely emulates a "regular" spring return relay. So if it is not held on it will return off.

So is the OTL a latch?

Why not? unless some force acts on it, it will stay on. Their is no need for a holding circuit as there is no spring return trying to turn it off as in the OTE.

I don't like the OTL , never have, I began to realize this dislike was because of a lack of understanding, then as I learn more and have focused on the OTL recently , I realize that I still don't like it.

It is not so difficult for me to hold an OTE on and then everyone can see what conditions are effecting the bit and any power down will clear the bit and thus unlatch it.

SOme of my dislike of the OTL is also from so much abuse by those who wrote programs I had to fix and patch.

At one point I HATED OTLs and the people who used them.

Of course now I understand this was the source of my imcome that week.

And the LAD programming symbols WERE made to resemble relay logic diagrams so that they would look like relays. This was intentional to help electricians and non programmers understand what was going on. And if you program simple circuits with comments this is true.

The FUNCTION of these parts however are much closer to boolean algebra.

I use the terms AND and AND NOT in place of NO and NC unless I am referring to an actual piece of hardware.

It also helps to read the line backwards starting at the OTE.

Motor is ON if.......AND S1, AND valve2, AND NOT level hi.

I have converted actual conversation directly from English into ladder on several occasions as the supervisor discribed what he wanted to happen.

It's easy if you tune your ear and train the answering party to answer your specific questions.

"Under what conditions does this motor need to be on?"

Then wait while he writes the code for you.

If it is just you talking to yourself, you call it anything you like, but when you interface the rest of the world someone has to define these terms and then we all have to agree on the meaning of the terms in order to avoid confusion.

If we both know what an ----] [ ----- does , I don't care what you call it.

The only damage is others who do not understand will pcik up the bad habit and spread the missunderstanding. Which is one of Ron's concerns.


Not sure if any of this will help or not.

 

[robertmee]

Thanks for the help so far everyone. So the recommendation seems to be that I should not latch the output coils. In this case, should I have a separate rung for each output coil, and use XIC in parallel for the bits that turn on each output? That way, if I needed to turn on an output in different stages of the program, I could do it that way? For example, the "fingers open" output needs to be held on thru a few stages, so should I just put XIC contacts in parallel for the bits for each stage the output needs to stay on for? This would also seem to solve the issue of having a coil for the same output used multiple times in the program.
Thanks!

Yes, that is a much safer and preferred way of manipulating your output addresses. You can certainly use the OTL/OTU instructions to step through your sequencing, but then use those sequence bits to turn on your Outputs with regular OTEs. Just be sure to include logic that on a fault or PLC mode change that you put your step logic to a safe known state, which will inherently turn off/on the outputs needed for that safe state.

 

[RH68]

Thanks for the help guys. I re-wrote the program using separate rungs for the outputs that aren't latched and didn't use any double coils. Everything seems to be working properly now.