Mike in Canada

First off, let me say that I appreciate the response.

 If  I was writing this in any procedural language then what you put above would make perfect sense.   It doesn't seem to make sense to me for ladder logic, but it might be reminiscent of one of my earlier trials where I had something like:

[I1]---[/Q2]----[/Q3]------------(M1)

[I2]---[/Q1]----[/Q3]------------(M2)

[I3]---[/Q1]----[/Q3]------------(M3)

M1--------------------------------(Q1)

M2--------------------------------(Q2)

M3--------------------------------(Q3)

The result was the same, but maybe adding /Qx and /Qy on the Qn lines would help... another layer of only-one-at-a-time...  I will try that.

The code you have put down will not work. There would have been a better chance if you were using /Mn instead of /Qn. The main trouble is that the coil in line 1 does not get its value by the time you read line 2. 

I did warn you to avoid using LAD on the LOGO! Please take my suggestion for building a sequencer more seriously. Better to rather use FBD.

Am I the only one getting constant "internal server error" issues when I access the forum?

Anyway, I think I have figured it out.

The code is NOT elegant, because I was adding all kinds of extra checks here and there... but it works.  The only thing you have to do to make the code work is it needs the three demand inputs to be off at the same time, then it starts working properly, and from there it seems perfect.

These constant "internal server error" issues are killing me.   This is my last attempt to upload.

I think I have figured it out.

I have been having a HECK of a time trying to access this forum.   Constant internal server errors.  Horrible.    I installed Chrome to use instead of Firefox and that seems to have fixed the problem.  I'm not sure what the deal was, there, but at least I can log in.

I solved my problem, so I'm going to upload it here so that the next person doesn't have to reinvent the wheel.

This version works, but it has two issues - you need to 'reset' it by having it start with no demand.  If it starts up with all of the demand inputs turned on it will freak out.   As long as it can reach a zero-demand state then it will get its bearings and it will be fine from there - even with demand on every input.

The other issue is just that it has a lot of double-checking going on.   It's not the leanest programming that I have done - that's for sure - but it works, and I haven't bothered going back to try to trim out what might not be needed.   Anyway, the working version is attached.