Simple question...need a simple answer

A lot comes down to personal preference. When I have a lot of bits turning on the same output (say more than 5 or 6) I like to use a binary word so I can keep the rung of code on the screen. You can also use a combination. ie set aside a file such as B33 and call it binary words. Use the bits only for this purpose, this gives you a choice of using the discrete bits for your control or if there are a lot of them you can drop back to the word. The bits are still descripted as what each one is, the word is descripted as what the word does and the file is descripted so hopefully no-one starts using the bits for other purposes.
Regards Alan Case
 
Alan Case said:
Now a question for the beginners. Why use NEQ instead of GRT
Regards Alan Case

I wrote an answer but you said beginners, I may be slightly past that point. I will say 2's though.
 
Hey remember me :) I was the one who asked for a the simple answer, not a debate on which was better. I tried the parallel bit thing but there is a timer also in that rung which is not allowing the parallel bits to continue. Thanks again.......
 
Hi Emesis. Sometimes we do get carried away, but we are trying to give you different ways to do a simple job. If you take it all in and then make up your own mind then I am sure you will benefit from the whole discussion.
Hi Ron, You are definitely past the beginner stage but I am not sure what you mean by 2's though.
Regards Alan Case
 
I will take a guess at what Ron is meaning, possibly 2's complement, not sure of the exact descripition, but if all bits are on, then the value of the word is -1, hence so if you use a GRT ( > ) in the PLC that I use, then the statement will not be true. The same will apply if you use >= ( greater than or equal to )

to make it easier for people who didn't program the machine to be able to troubleshoot it while the programmer is busy or on vacation.

If the code is well documented & commented ( perhaps the same thing ) then this should not be a major issue.

Perhaps if the electrician is willing, training could be given on PLC's, I am sure a there is a large percentage here that are electricians ( bubbas as they are sometimes referred to )that are very competent in PLC's.
 
Perhaps if the electrician is willing, training could be given on PLC's, I am sure a there is a large percentage here that are electricians ( bubbas as they are sometimes referred to )that are very competent in PLC's.


Sorry to post a little off topic again.

I didn't mean to imply that electricians weren't good with plc programming. My boss is a licensed Master Electrician, and he does all the RSLogix500 and 5000 programming between both plants at the factor I work. At least, until I got hiered. I have a BS in EE, and am currently an apprentice under him, and took over the programming at one of the two shops, to make it easier for him, and quicker so the people at one shop did not have to wait.

It's just that, while for some people (A lot of the veterans on this board maybe?) the basic ideas of Ladder Logic, and simple things they take for granted like Binary, knowing which way the bits are organized in a word, (MSB->LSB) are easy to understand, they just don't come easy to others. The 3rd electrician where I work is a Journeyman (was apprenticed under the boss as well) and has tried to learn and understand PLCs. He just has trouble grasping some of the actual boolean logic when represented in ladder form.

I guess this just shows how a lot of the stuff is on a case-by-case basis, but it's something to think about when you have multiple, sometimes inexperienced, programmers and troubleshooters.


Hey remember me I was the one who asked for a the simple answer, not a debate on which was better. I tried the parallel bit thing but there is a timer also in that rung which is not allowing the parallel bits to continue. Thanks again.......

Hmmm, I think it may be best to try and program it so that these Bits are only true when you want the action to be done. Right now it sounds like they are true when you want the action to start, and stay true long after they are done, probably until the cycle is finished.

If they were only true as long as the action needed to be done, the first bit would time the timer, then by the time the second bit came around the first would be off and the timer would have reset itself.

I really wish I had RSLogix500 at home so I could show you a really nice, very customizable method of programming sequencial machine cycles. I know the method probably has a name, but I don't know the name. It basically uses Bits for the "Do Step" and then once the step is complete, it disables the "Do Step" and holds a "Done Step" bit in until the cycle is finished out, at which time it resets itself and waits for another cycle. Maybe someone else here uses it, I'm sure there is at least one.

Edit: Also, the "Done Step" is also a permissive for the next "Do Step". I'm hoping someone around here uses this method or knows a name for it.
 
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EmesiS said:
I'm using a MicroLogix 1000 and I want to use the same output in different sections of my logix. Basically a timer triggers that output on and off then it goes to the next process. Then later on in the logix it needs to be triggered again in a repeat process. But because it is the same output it is not coming on. I can change it to a different output in the logix and the ladder works fine. I'm using different bits to trigger the output, but the output is cancelled out in the logix. There should be a way to do it without using subroutines or sequencers but I just can't seem to figure it out. So does anyone have any suggestions...thanx.

If you could post a snippet showing the timer logic, we can help you a lot easier. Does the output need to do the on/off routine each time?
 
EMESIS,

I sense from reading your first couple of posts that you may have a misunderstanding of the PLC scan cycle.

All of your logic will execute very quickly, many, many times per second. The Micro doesn't turn on the REAL outputs until the end of each scan. So, whatever you do to a single address during the program doesn't affect actual control until the end, so the output will take the last state that was updated by the ladder logic.

Have a look at the LEARN PLCS tab at the top of this page

especially the HOW IT WORKS link:
http://www.plcs.net/chapters/howworks4.htm

Good luck, and welcome to the forum.
 
Ok Ken here is a portion of what I'm trying to do. There is a gum arabic spray and then a powder coat, I need to repeat that process 3 times. Once again please understand I'm a newbie so I'm trying to do this as easy as possible. Everyone has to start somewhere, right? I welcome all ideas but have mercy on my brain cells, I only have 3 left. Sorry for the picture but I'm at work so I'm limited on the programs available, hope it can be read, if not I'll try to get a better one. Thanx to all.....


cdrum.jpg
 
If you're trying to get the spray gun to fire again for a set time, just add your other bits in parallel with B3:0/2, or add another timer and parallel the timer timing bit with your existing timer timing bit T4.2.TT

It would help if you could be more specific.
Such as when x happens then y does this, then when z happens y does this again for k seconds. Be as exact as possible, it's hard to decipher exactly what your doing from the information given so far.
 
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Let's try another method. With RSLogix you can print a report, you can go to www.pdf995.com and download software that will act as a printer but print to a pdf file. You can then upload that pdf file to this site where others can see what you are attempting to do and offer suggestions.
 
...here is a portion of what I'm trying to do. There is a gum arabic spray and then a powder coat, I need to repeat that process 3 times...


Try something like this:
EDIT: I FORGOT TO RESET THE FIRST TIMER EACH TIME THE COUNTER INCREMENTS. ADD XIO T4:3/DN AHEAD OF TON T4:1

3Cycle.JPG



Now, it doesn't provide a way to interrupt the process but it may give you an idea...
 
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OK thanx for all the suggestions....I had to go an a call for our Hayssen bagger. Came back to my office and had all these suggestions, you guys must live online, which is a good thing for me :) I'll download that file and post a .pdf next time. Thanx again.
 
Ok thanx OkiePc, I was just about to message you about that same thing. I will continue to test, and I sure appreciate you taking the time to help.
 

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