Logic Help

Hello,

I have been asked by the plant to evaluate a new product pattern. I have never seen the logic stepped through using the scan time before. I have also never used the masked fall thru before. The PLC is a PLC 5/30. I am only going to be in plant through tomorrow 7/7/2015 evening. If someone would be willing to look at the code and see point me in the right direction that would be wonderful!

There are only 400 lines of logic and most of those are simply different turners, stops etc. They are all timed off the same scan time logic and that is where I am missing something. I think there are probably only 10 critical lines of code if you know what your looking at.

Thank you!

Unfortunately, I don't feel that anyone on this site can actually help you. 1, you did not actually post your program, so it's literally impossible for us to look through it, and 2, the problem that you are having is stated very vaguely, to the point that I don't actually understand what your problem is.

Not so sure SandwichMagic....

A purchase order for flights and hotels and a good hourly rate to visit the plant and work in real time, might sway some of the programmers on here to work with daviper1996 and assist in the solution.......

I wish

I think that is a wonderful idea and is what I am doing!

I also can't post the code but could pass on a portion privately...

I have been working and staring at the code for a day now and am comfortable with about 90%.

What I am missing is how the code is moving a particular set of words. I THINK it is related to the SQO function but not entirely sure.

Quick explanation.

The program loads a pattern file from N21:XXX to N20.2 for X number of words depending on pattern. There is also a N31:XXX which moves to N30.2 for the same amount of words etc.

An SQO statement R6.1 moves N20.1 to N20.0. R6.2 moves N30.1 to N30.0 respectively. The sequencer is set to 100 but resets is position on transition between layers.

A bit further down in the logic there is a copy statement moving N20.0 into N25.823 and N30.0 into N35.823

The program uses the PLC scan time to move a set of words through N25:823 and moving toward N25:500. As bits of the words passed to N25 make their way up toward N25:500 various machine functions are timed off of the word position.

I can not figure out how the value that was placed in N25:823 is moving to N25:822 and then N25:821 etc.
..

http://www.plctalk.net/qanda/showthread.php?t=68881

Here is a previous thread that may help in the understanding of the SQO instruction.

Hope this helps,
Garry
http://www.accautomation.ca

I took a look at the thread and thank you, it clarified some of my questions. I still do not believe it explains how the words are being moved around inside of N25 and N35 respectively. Somehow once every scan N25:823 is moved to N25:822 and the next package word is placed into N25:823. On the next scan N25:822 moves into N25:821 and N25:823 is moved into N25:822 and the next package is placed into N25:823.

The new package always starts in N25:823 and then moves in order thru the file. When the word (in which each bit actuates a different part of the machine) gets to position defined in the ladder logic an output is made and sealed in until another package with an off bit for that piece of machinery.

Example:

I want to raise a stop at a predetermined time. I would add a subrung with this patterns enable bit followed by XIC (N25:725/10). If I want that stop to be up for 25 scans then I would add a subrung past the sealed in section of code with the patterns enable bit followed by XIO (N25:725/10)

But how is the word moving through N25:823... The SQO steps reads through a file but places the word it copies into the same location each time. The program then copies the word copied by the SQO into N25:823...


I do not see any FIFO statements etc. There is an STI statement which calls the other ladder file in the program. From what I can tell though that only handles a higher speed portion of the machine.

I could PM the code if it helps...

oops.. That second N25 should read N25:700/10

Are there any MOV instructions referencing these addresses? Sometimes a shift register is implemented by one or more MOVs. As in : MOV N25:822 N25:821 2. This would produce the effect you're describing.

Thank you!

Thank you for the help I certainly learned a few things following your pointers. What was staring me in the face was the COP statement immediately following the move statement....

1.) Move the pattern into #N20.2 for X number of words based on how many packages are on that layer.

2.) False to True transition takes an SQO statement and iterates through N20 starting at N20.1 with a target of N20.0

3.) False to True transition uses a MOV statement to take N20.0 and move it into N25:823

4.) A COP statement takes #N25:325 to #N25:324 for 500 words on every scan.


I kept overlooking the COP statement as I have never used it in this fashion. What are the advantages/disadvantages of the COP statement VS a Shift Register?

You've already discovered one disadvantage of the COP instruction. A shift register instruction probably would have given a person who didn't write the program a better idea of the original programmer's intent

COP moves words(16 bits), Shift register indexes bits (one bit at a time).

I see and the SQO statement only moves one word at a time so you would have to iterate through which would be inefficient as well as eat of scans which is how this whole thing works in the first place.

Thank you all again!