Simple Lader Logic Question! PLEASE HELP!!

[geniusintraining]

...just wondering ... how did you keep track of "five scans" for each of the systems? ... did you use the "single-step" method that I mentioned above? ... if not, any difference between the fixed and the modular systems might be a result of simply "miscounting" how many scans had been processed in each one of the systems ...

Ok the other Ron this time (Beaufort),

why did you ask about "five scans"?, I found the test single scan in the AD software (never used it before), when I run the program besides the first scan there would only be 2 scans 'images' ...correct?, is there a issue with my (scan)thinking?

Anyone have lab equipment that is capable of checking the differences?

The other scan was inverted, beside E

 

[Ron Beaufort]

Greetings geniusintraining ...

why did you ask about "five scans"?

because the original poster mentioned:

I need the values for A,B,C,D,E after 5 scans.

actually (as others have said) the pattern keeps repeating itself on alternate scans ... specifically, any odd number of scans will give the same results as any other odd number of scans ... and conversely, any even number of scans will give the same results as any other even number of scans ...



that’s assuming (gosh I hate that word) that I really understand the problem in the first place ... in any case, the code shown in my picture above is what I ran - and I started with all of the bits in a “0” state ... I guess that’s what the original poster intended ...



offline for tonight ... party on ...

 

[mvandyke]

With RS500 I got the result that I expected.
But I then tried it with the Zelio programmable relay and got the same result SID did with the Pico.

I even tried to trap A, but it never came "on".

edit:
I found the following in the Programming Rules for the Zelio;
"The R (Reset) actions of an automation function always take priority over S (Set) actions applied to the same function at the same moment"
No matter where the Reset is located in the scan,(above or below) the Set; "A" never comes "on".

 

[OZEE]

That's one reason why this homework question needs to be refined. Not all PLC's (or programmable relays) scan the logic in the same way. Whenever this homework question is posted here, one of the first questions that is asked is "What is your PLC?" This question cannot be answered generically!

 

[Jimmie_Ohio]

personally I'd have bet some serious money that both SLCs would work the same way ... I don't have a "fixed" to try this out with - but if I can possibly round one up from a friend, I'd love to see what causes any difference in operation ...

Several years ago, I was working with a customer who was standardized on SLC500 modular PLCs using the 5/03 processor. They had a smaller, but similar job for me to program. They chose to use the "new" MicroLogix.

I recall taking a "working" SLC500 program form another machine, changing the I/O to reflect the new processor, and downloading it. Nothing seemed to work quite right. We were using a lot of retentive timers with the reset rungs at various places throughout the ladder.

I solved the problem by putting all timer resets at the end of the program. Never spent the time that Ron et al spends tirelessly figuring all of this out. I simply attributed it to a different "scanning" method the different processor used.

 

[Ron Beaufort]

Never spent the time that Ron et al spends tirelessly figuring all of this out.

ahhh ... but you're missing the thrill of the chase ...