Anyone do any PLC stuff? How long did it take you to learn abouat the programming, the wiring, etc, to get a PLC to accomplish stuff you wanted it to? I'm just asking, beacuse that's one of the major thigns we're workign with this year...Alan Bradley PLCs...my group is having nothing but problems with the PLC we have. Apparently it needs to be reset.
PLCs...
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joec
Member
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- Lancaster, PA
Re: PLCs...
Are you using RSLogix as application software? Also, what PLCs are you working with...PLC 5, Contrologix...? Please provide some specifics about your applications.
Are you using RSLogix as application software? Also, what PLCs are you working with...PLC 5, Contrologix...? Please provide some specifics about your applications.
paul
Senior Member
- Location
- Snohomish, WA
Re: PLCs...
I programmed Allen Bradleys for an OEM before I went into the electrical trade. I learned how while trouble-shooting a program over the phone. After that, I started to write our programs and also programmed for air-logic machines. There are many different PLC's but the language is pretty much the same. Or at least it was 15 years ago.
I programmed Allen Bradleys for an OEM before I went into the electrical trade. I learned how while trouble-shooting a program over the phone. After that, I started to write our programs and also programmed for air-logic machines. There are many different PLC's but the language is pretty much the same. Or at least it was 15 years ago.
petersonra
Senior Member
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- Northern illinois
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- engineer
Re: PLCs...
I've been doing this for a living for over 20 years now. Its become second nature by now.
If you can give more specifics I might be able to help. PM if you want.
I've been doing this for a living for over 20 years now. Its become second nature by now.
If you can give more specifics I might be able to help. PM if you want.
Re: PLCs...
Well, I really didn't have any specifics in mind...but thanks for the offer of help--I'll keep it in mind. I was just more ranting, and curious to know about the learning curve of working with them. Beacuse as of now, I'm not feeling too confident that I could do anything too special...all we're doing right now is NC and NO switches for lights, then a selector switch, a drum controller...which, since our PLC is like malfunctioning, we have not got around to yet. Just piped in the lights and pulled some 110 to them so far. I guess I shouldn't stress about not knowing very much yet--we haven't been working with them that long. And I rememebr last year, when we did resedential stuff, I was lost at first, but then I caught on and excelled--so I would expect the same from the industrial/commercial stuff we are doing this year. I mean...like when I talk to our tacher about doing stuff, it's like WOW...but I just have to keep in mind that he's been doing this for a long time, and he has a ton of experience--so no wonder it comes to him so quickly and easily. So what have you guys all done with PLCs? How much experiecne you got? Any advice for someoen just starting. I've heard the programming is pretty much the same from PLC to PLC, which, thankfully, you guys have confirmed.
Well, I really didn't have any specifics in mind...but thanks for the offer of help--I'll keep it in mind.
I was just more ranting, and curious to know about the learning curve of working with them. Beacuse as of now, I'm not feeling too confident that I could do anything too special...all we're doing right now is NC and NO switches for lights, then a selector switch, a drum controller...which, since our PLC is like malfunctioning, we have not got around to yet. Just piped in the lights and pulled some 110 to them so far. I guess I shouldn't stress about not knowing very much yet--we haven't been working with them that long. And I rememebr last year, when we did resedential stuff, I was lost at first, but then I caught on and excelled--so I would expect the same from the industrial/commercial stuff we are doing this year. I mean...like when I talk to our tacher about doing stuff, it's like WOW...but I just have to keep in mind that he's been doing this for a long time, and he has a ton of experience--so no wonder it comes to him so quickly and easily. So what have you guys all done with PLCs? How much experiecne you got? Any advice for someoen just starting. I've heard the programming is pretty much the same from PLC to PLC, which, thankfully, you guys have confirmed. bphgravity
Senior Member
- Location
- Florida
Re: PLCs...
I would study a little on binary adressing, reading and writing ladder logic, BCD math, Boulon Logic, Communication links, analog to digital controls, basic cpu and I/O control functions, and a some concepts about memory.
I am a fan of Omron C-Series PLC's and components. I find them to be much more user friendly as compared to Alan Bradley systems.
I would study a little on binary adressing, reading and writing ladder logic, BCD math, Boulon Logic, Communication links, analog to digital controls, basic cpu and I/O control functions, and a some concepts about memory.
I am a fan of Omron C-Series PLC's and components. I find them to be much more user friendly as compared to Alan Bradley systems.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: PLCs...
BTW, there are many reasons why certain AB PLCs will shut themselves off. Depending on which model it is, often they will tell you why.
The older ones (like PLC2 and SLC100 models) do not have this capability but SLC5 and PLC5 units do.
If you have the programming software you can hook up to the CPU and it will tell you exactly what happened and usually allow you to restart the CPU. Sometimes this is not especially helpful, as some of the faults are rather obscure, and there is no way for you to fix the problem.
BTW, there are many reasons why certain AB PLCs will shut themselves off. Depending on which model it is, often they will tell you why.
The older ones (like PLC2 and SLC100 models) do not have this capability but SLC5 and PLC5 units do.
If you have the programming software you can hook up to the CPU and it will tell you exactly what happened and usually allow you to restart the CPU. Sometimes this is not especially helpful, as some of the faults are rather obscure, and there is no way for you to fix the problem.
Re: PLCs...
I have only programmed a few types of PLC's but I think the Allen Bradley is definately the Cadillac. It does math operations other PLC's can only dream about. And the Rockwell (AB's software division) programming software has some very advanced features. The ability to compare two different programs is one that comes to mind.
However, all these features make for a steeper learning curve. If your PLC doesn't seem to work, it may be:
1. The PLC is not working like you said. Try another PLC.
2. Something is wired wrong.
3. You just need to learn a little more about the PLC and software you are using.
For example, one PLC I programmed was connected to a relay. The relay would not turn on even though the light on the PLC indicated the output was on. Measuring the voltage at the PLC pin, I got 6V instead of the 12V I expected. I thought I had a bad PLC. Called Tech support and had them convinced it was a bad PLC. They tried my program on one of their PLC's, and decided they had a bad PLC. They even started taking about a manufacturing defect that may have caused a bad batch.
I finally found the problem. I had one rung that turned the output on on one scan, and another rung that turned the output off on the next scan. The output keep toggling from 0V to 12V and back (which explained the 6V reading). Although the ouptut light appeared to be on, it was really flashing too fast to see. I guess my point is that it often seems like the PLC is bad when it is really just something very simple (but very hard to find).
The only real problems I have had with AB PLC's involve communications to PC's. On one project, the programming software wouldn't update fast enough, and it keep showing outputs at the wrong state. Another project (with Rockwell's HMI software), it kept missing data the PLC would send to it.
Steve
I have only programmed a few types of PLC's but I think the Allen Bradley is definately the Cadillac. It does math operations other PLC's can only dream about. And the Rockwell (AB's software division) programming software has some very advanced features. The ability to compare two different programs is one that comes to mind.
However, all these features make for a steeper learning curve. If your PLC doesn't seem to work, it may be:
1. The PLC is not working like you said. Try another PLC.
2. Something is wired wrong.
3. You just need to learn a little more about the PLC and software you are using.
For example, one PLC I programmed was connected to a relay. The relay would not turn on even though the light on the PLC indicated the output was on. Measuring the voltage at the PLC pin, I got 6V instead of the 12V I expected. I thought I had a bad PLC. Called Tech support and had them convinced it was a bad PLC. They tried my program on one of their PLC's, and decided they had a bad PLC. They even started taking about a manufacturing defect that may have caused a bad batch.
I finally found the problem. I had one rung that turned the output on on one scan, and another rung that turned the output off on the next scan. The output keep toggling from 0V to 12V and back (which explained the 6V reading). Although the ouptut light appeared to be on, it was really flashing too fast to see. I guess my point is that it often seems like the PLC is bad when it is really just something very simple (but very hard to find).
The only real problems I have had with AB PLC's involve communications to PC's. On one project, the programming software wouldn't update fast enough, and it keep showing outputs at the wrong state. Another project (with Rockwell's HMI software), it kept missing data the PLC would send to it.
Steve
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: PLCs...
You have not lived until you open up a couple thousand rung program someone else wrote and its full of latches, unlatches, and one shots.
You tend to see this where the guy that wrote it is a hack, and its not so awful when its a few hundred rungs. But when the printout is 6 inches thick and the whole program is written this way I just want to cry.
I am amazed they ever get this style of code to work, but I guess the trial and error appraoch to programming eventually works. Its just a nightmare to maintain and change.
You have not lived until you open up a couple thousand rung program someone else wrote and its full of latches, unlatches, and one shots.
You tend to see this where the guy that wrote it is a hack, and its not so awful when its a few hundred rungs. But when the printout is 6 inches thick and the whole program is written this way I just want to cry.
I am amazed they ever get this style of code to work, but I guess the trial and error appraoch to programming eventually works. Its just a nightmare to maintain and change.
B
bthielen
Guest
Re: PLCs...
For the past 15 years I've worked with just about any PLC one could imagine as well as writing logic and troubleshooting mine as well as others' programming and hardwiring. Mostly the latter. The program structure continues to change all the time from simple ladder logic, to statement list logic, to sequential function chart logic, to ...
One thing to keep in mind. Give 20 different designers the same task and you'll get 20 different programming styles and methods. They all work and they all are functional. No one method is better than another.
We tend to think so because we each analyse situations in our own unique way. As a result, we may think another design is a poor design when in reality it may be better than our own. To best understand someone else's programming requires an ability to get into their head and think like they did.
So to answer the first question of this thread, "How long did it take?" You never stop learning. Practice...practice...practice...
Bob
For the past 15 years I've worked with just about any PLC one could imagine as well as writing logic and troubleshooting mine as well as others' programming and hardwiring. Mostly the latter. The program structure continues to change all the time from simple ladder logic, to statement list logic, to sequential function chart logic, to ...
One thing to keep in mind. Give 20 different designers the same task and you'll get 20 different programming styles and methods. They all work and they all are functional. No one method is better than another.
We tend to think so because we each analyse situations in our own unique way. As a result, we may think another design is a poor design when in reality it may be better than our own. To best understand someone else's programming requires an ability to get into their head and think like they did.
So to answer the first question of this thread, "How long did it take?" You never stop learning. Practice...practice...practice...
Bob
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: PLCs...
Its no different than if you went out to look at some electrical work and none of the conduit was straight or plumb. It still works but its the sign of someone who is not very good or just does not care.
I beg to differ. Just because something eventually works does not make it a well thought out or well executed piece of code. There are certain things I often see in programs written by others that instantly mark them as hacks. Use of lots of oneshots, latches, and unlatches to get rid of scan races is one sure sign the programmer is a hack.
Its no different than if you went out to look at some electrical work and none of the conduit was straight or plumb. It still works but its the sign of someone who is not very good or just does not care.
Re: PLCs...
I don't necessarily consider one-shots and latches a bad thing. But since you brought up bad programming, I once opened the program for an AB PLC that was on a piece of industrial machinery (so many of these were sold with the exact same program). The program was about 1000 subroutines. Each subroutine had at most 2 rungs (usually a latch and unlatch). Some rungs had the same contact both NO and NC on the same rung (so the output was never on or always on). I'm still not sure if that was the worst program I have ever seen, or the best.
Steve
I don't necessarily consider one-shots and latches a bad thing. But since you brought up bad programming, I once opened the program for an AB PLC that was on a piece of industrial machinery (so many of these were sold with the exact same program). The program was about 1000 subroutines. Each subroutine had at most 2 rungs (usually a latch and unlatch). Some rungs had the same contact both NO and NC on the same rung (so the output was never on or always on). I'm still not sure if that was the worst program I have ever seen, or the best.
Steve
B
bthielen
Guest
Re: PLCs...
I understand your point, petersonra, but I also agree with Steve that one-shots, latches, etc., are not always bad. Each serves its purpose.
I wrote my comments a little hasty without much forethought. Programming can become very confusing and hard to follow if not laid out well, just as you related it to poorly designed or installed hardwiring. Imagine troubleshooting an electrical circuit that zig-zags its way unnecessarily through a dozen j-boxes and terminations in different rooms before reaching its destination only a few feet away. Functional does not necessarily mean quality design.
I have a hard time however when someone labels another simply because their method differs and the individual disagrees. There is more than one good way to a solution and I'd like to meet the individual that has the one and only perfect way.
Humbly, Bob
I understand your point, petersonra, but I also agree with Steve that one-shots, latches, etc., are not always bad. Each serves its purpose.
I wrote my comments a little hasty without much forethought. Programming can become very confusing and hard to follow if not laid out well, just as you related it to poorly designed or installed hardwiring. Imagine troubleshooting an electrical circuit that zig-zags its way unnecessarily through a dozen j-boxes and terminations in different rooms before reaching its destination only a few feet away. Functional does not necessarily mean quality design.
I have a hard time however when someone labels another simply because their method differs and the individual disagrees. There is more than one good way to a solution and I'd like to meet the individual that has the one and only perfect way.
Humbly, Bob
Re: PLCs...
New Jersey is installing a Alan Bradley PLC 5 system on a bridge rehab there doing. I've been to two classes on them so far. There training classes great and instructors are very knowledgeable.. Further more the material they give you is great, easy to use flow charts, everything is well spelled out. Much easier than the SQ D symax system the state has now.
New Jersey is installing a Alan Bradley PLC 5 system on a bridge rehab there doing. I've been to two classes on them so far. There training classes great and instructors are very knowledgeable.. Further more the material they give you is great, easy to use flow charts, everything is well spelled out. Much easier than the SQ D symax system the state has now.
Re: PLCs...
A oneshot is a thing in a PLC program that will Go on for only on program scan once the rung it's in goes true(energized).
A latch is went you have a switch that would turn on that load , however you need another switch to de energize that load
oneshot rung might look like this
----/--------------(O)-----------
where the / would be a switch and the (O) is the bit your making true
Latches
-------/-----------(L)-------- 1
-------/-----------(U)-------- 2
turning switch on in 1 would turn that latch on and it stays on until switch in 2 is turned on and then the (U) unlatch bit would turn off the load
By the way in PLC programming remember the last rung wins, that is if one rung is telling the plc to run something and another rung further along is tell it no the plc goes by the last one.
A oneshot is a thing in a PLC program that will Go on for only on program scan once the rung it's in goes true(energized).
A latch is went you have a switch that would turn on that load , however you need another switch to de energize that load
oneshot rung might look like this
----/--------------(O)-----------
where the / would be a switch and the (O) is the bit your making true
Latches
-------/-----------(L)-------- 1
-------/-----------(U)-------- 2
turning switch on in 1 would turn that latch on and it stays on until switch in 2 is turned on and then the (U) unlatch bit would turn off the load
By the way in PLC programming remember the last rung wins, that is if one rung is telling the plc to run something and another rung further along is tell it no the plc goes by the last one.
Re: PLCs...
I cut my teeth on those circuits decades ago. In its most basic form, the one-shot switches on for a predetermined time after it is triggered, then it switches off automatically.
A latch is a circuit which stays in one state until it is set or reset by external triggers. It is something like a latching relay in function.
Now in PLCs, the use of the terms is probably a bit different. I know how PLCs work but have never programmed one. So bear in mind that I am giving you the most basic examples of these circuits.
I cut my teeth on those circuits decades ago. In its most basic form, the one-shot switches on for a predetermined time after it is triggered, then it switches off automatically.
A latch is a circuit which stays in one state until it is set or reset by external triggers. It is something like a latching relay in function.
Now in PLCs, the use of the terms is probably a bit different. I know how PLCs work but have never programmed one. So bear in mind that I am giving you the most basic examples of these circuits.
shocker3218
Senior Member
Re: PLCs...
sometimes I wonder if a history lesson and learning to program old plc's such as the 184 modicons that only allowed 4 elements/rung and used thumbwheels to pull up the rungs, would be beneficial to those that are learning to program. Start with the basic, then work your way up.
Yes, Ive seen a lot of OLD plc's. German model Allen Bradleys, modems that you put the phone handset into, core memories that failed often, and others.
I really appreciate the benefits and advantages of the newer ones, after going through some of those.
sometimes I wonder if a history lesson and learning to program old plc's such as the 184 modicons that only allowed 4 elements/rung and used thumbwheels to pull up the rungs, would be beneficial to those that are learning to program. Start with the basic, then work your way up.
Yes, Ive seen a lot of OLD plc's. German model Allen Bradleys, modems that you put the phone handset into, core memories that failed often, and others.
I really appreciate the benefits and advantages of the newer ones, after going through some of those.
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