Next Step... PLC's
Paul Strohman
Posts: 4
My students are using the Boe-Bot· for the PLTW curriculum. We perform the activities in the curriculum and I typically give each student additional projects and a·final project based on their abilities(differentiated instruction and testing). I want to take what I see as the next step, PLC's. What has been your experience implementing PLC training? I have 30 years of 'old school' electronics experience but, no PLC experience. Obviously I need some training and that has been arranged. What do I 'need' with regards to hardware and what kind of 'lab' projects are there out there to choose from?·I have 12 students and 6 Allen Bradley MicroLogix 1500 PLCs. I am open to aquireing some of the Parallax Stamp PLCs to further augment instruction.
Comments
I deal with AB PLC's every day at work. Just to get a little background from you... What exactly are you trying to get them learn? Put another way, are you teaching about automation in general, or doing the more industrial approach or this simply a logic/tech class? Are you trying to tie in what you have learned with the Stamp with what you are about to teach with the PLC's?
I tend to go with your idea of going with the Stamp PLC then transition to AB products. You are comparing apples to baseballs really. Programming and RLL are two different beast that (for me at least) use two different parts of my brain (basic logic aside). It still takes a second or two for me to jump out of microcontroller programming world into PLC RLL world. I would go with the fundamentals and teach (with stamps) what can be accomplished in logic type scenarios within industry.
I have quite a few resources for AB PLC's and know what it is like to make the transition from micro controllers to PLC's first hand. Let me know what direction you are taking and I might be able to hook you up with some resources.
PS: I hope you got all the software with those PLC's. That can be one of the most demanding and expensive parts... not to mention the learning curve with the programming environment in general. I took an entire class on just using their software... did not even get to the logic...
PSS: I just reread your post and caught the sentence about taking the next step... PLC's. IMHO, PLC's are pushed a little to hard in the fact that I see every day some one putting in a $800 micrologix to flash a light bulb or start a motor. Though it is industry standard, it makes me kind of sick when something takes 500 lines of ladder logic that could have been done with 20 lines of code... If I had to start a campaign it would be to bring microcontrollers into more mainstream industry. PLC's have a good perfect place in the world... but so do new faster micro controllers. The interface and packaging is why PLC's are still controlling almost every thing in industry. (Sorry for the rant... guess I had some built up PLC issues to get out.)
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Alex Burke
"Beware of computer programmers that carry screwdrivers." -Leonard Brandwein
This is a logic/tech class. I aim to tie in what the students learn using the Stamp to compare and contrast the capabilities and limitations of PLCs. I like the idea, as you wrote; "teach (with stamps) what can be accomplished in logic type scenarios within industry." I got these 1500s, free and would hate to not use them but, I could spring for some Stamp PLCs if that would help with the connections. I believe I have all the software and if not, I have a contact who can 'hook me up.' I understand your hesitance of using PLCs to make lights blink but truthfully, that is about all I can do right now with the resources I have available. I do have a Fischertekniks project incorporating limit switches.
I am currently teaching Digital Electronics using the Project Lead The Way curriculum and hope to some day add an additional PLTW course titled Computer Integrated Manufacturing™. Certainly, PLCs will be more applicable to that class but I would like to give the student (and myself) a little flavor of the world of automation.
For now, I'm talking blinking lights, starting/stopping motors, and limit switches. In the near future, process control.
First off, you are right, I would hate to not use the 1500's either. And keeping it simple with lights and small motors is GREAT for learning. In fact making any thing difficult would only discourage.
Second, instead of really putting out a lot of money for the stamp plc, (which very nicely incorporates every thing in a slick case with terminals (and i think opto isolators)... you could pretty much make one yourself unless you need it rail mounted. Save the money and buy 20 more Stamps.
Lastly, just a random thing that sounded neat to me to teach, would be to make a 'fake' assembly line or conveyor belt. You could constantly build on the assembly by starting out with starting and stopping the belt. Then 'if object' turn on lite... then 'count so many objects then turn belt off' etc. This starts out really simple and can get as complex as you want without a whole lot of money. Each student could have their own project on it depending on how well they grasp the concept. You can then use PLC's and/or stamps and compare the logic. In theory you really don't even have to have a big working monstrosity... maybe a small miniature unit would do. I think that would teach some great logic for the industrial world.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Alex Burke
"Beware of computer programmers that carry screwdrivers." -Leonard Brandwein
I also use Stamps and PLC's in an industreial setting.
The biggest diffrence (Besides $$$)·is thinking one line at a time (Stamps) and all at once (PLC's).
Ladder Logic·scans (exicutes) all the rungs (lines of code)·at once, and the Stamp does one line at a time following the program.
With ladder logic you need to keep track of the bottom portion of the ladder along with the top.
RLL programming helps (this allows turning on and off chunks of the ladder), but all active rungs exicute at the same time.
It was hard for me to picture Ladder Logic after spending·almost 40 years programing in·Basic.
The learning curve was intense. But I also figured it out, and I never had the oppurtunity to take any classes.
PLC's are widely used in industry, and AB is the top dog.
Some of the low end stuff while being overkill, sometimes is cheaper than the equivelent circuitry.
I have used a $99 'Brick' PLC to blink a light (E-Stop). It cost 1/2 the price of the 2 time delay relays and sockets I used to use.
(I use Automation Direct PLC Hardware. It is much less pricey than AB Stuff.)
The 'Brick has 8 inputs and 6 outputs and at under $100 is a steal.
For 1 of a kind projects it is great.
Now for the Stamp..With all the praise for the PLC I like the Stamp Better.
If you have a small number of I/O, but it is mixed voltages, and/or AC/DC the Stamp excells.
With a PLC the Brick, and I think the Micrologix is the same, all the I's and O's are the same...All AC or All DC, sometimes relays, 24 volts or 120/230 volts, and the I' and O's are fixed.
To get mixed I/O you need a Rack type system with I/O modules rated for each type of Voltage.
With a Stamp connected to Solid State Relay modules you can mix and match as your needs demand.
If you need 15 I's and 1 O, or 8 and 8 you can assign them as you wish.
I have been using Stamps on industrial machines longer than I hae been using PLC's (15 years vs 9 for PLC's)
I have never had a Stamp failure in the field (I have fried a bunch on the bench tho)
So in typical ham radio fasion (Making a short story long), teaching both has many advantages and few disadvantages. Apples and Baseballs!
I would be willing to donate one of my Stamp Industrial Control Boards to your class. You will need to supply the type of Stamp and the I/O Modules.
It uses Grayhill 70m type of Modules ( available from Digikey and others.)
Contact me if your interested.
I have attached a picture of one in use in Massachusetts.
Good Luck
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Alan Bradford ·N1YMQ
Plasma Technologies
Canaan NH 03741
www.plasmatechnologies.com
If I am not mistaken doesn't some one sell some kind of Ladder Logic software specifically for stamp? Have you tried it before? The only thing I really remember about it is that it was expensive. However that might be a good way of teaching both worlds. Have them do the same exercise in both basic and Ladder Logic to see the different viewpoints. They could then understand which style of programming fits different applications better and what it takes to accomplish the same task.
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Alex Burke
"Beware of computer programmers that carry screwdrivers." -Leonard Brandwein
I also use PLC's in industrial control and automation applications. Regarding programming, I have to differ regarding Alan's point that Ladder Logic will execute all rungs at once. I've been specifically taught that RLL(Relay Ladder Logic) executes from left-to-right and from top-to-bottom. Granted, the execution is pretty fast, but it is happening one step at a time. All documentation I have supports this as well and my instructor specifically taught us to plan around it. No offense or argument intended, I'm just reporting my experiences.
All the best,
Tim
I teach a microcontroller and PLC course for my industrial clients.
We usually start out with the Stamp based controllers to show the Basic language concepts then move to a commercial PLC. The Stamp PLC is a fine product but does not move your students to the ladder logic and deterministic programming of an industrial PLC.
In my opinion, you'll get significantly bigger bang for the buck using the Automation Direct "CLICK" plc and software. The hardware is only about $70 and the full-featured software is free.
PM me and I'll send you some pics of the PLC trainers I built for the courses.
Cheers,
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Tom Sisk
http://www.siskconsult.com
·
You are technically correct in that the PLC exicutes one line at a time. And it is very fast.
But the program·acts like an electrical circuit and each rung reacts based on its own contents and not waiting for the rung above it to finish before exicution.
The Ladder Logic mimics the relays that were used on the old control boards of the 30's to 60's. That is why the ladder symbols resemble relay contacts and coils.
Each PLC rung looks like the relay circuit it replaces.
I am no expert in PLC Programming, and have been doing it for less than 10 years, no offense taken. I can still learn a two or thing. (And cant spell worth a D--n)
Some things are easier in Stamp and some in PLC.
Alex,
I have seen somewhere about a PLC language for the stamp, but never explored it. Ands the suggestion of learning to acomplish the same task using both is a good idea.
Thanks,
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Alan Bradford ·N1YMQ
Plasma Technologies
Canaan NH 03741
www.plasmatechnologies.com
I have not used the Click stuff, but with the extreme noise of the Plasma Cutters, I will stick to the Bricks and 205's when using a PLC.
A plasma cutter starts with a small lightning bolt and the possible problems with PLC failure out weigh the small cost savings.
As for a teaching tool you cannot beat the Click for price. I forgot the programming suite was free.
thanks,
▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
Alan Bradford ·N1YMQ
Plasma Technologies
Canaan NH 03741
www.plasmatechnologies.com
No offense taken this direction either, this is just good (and appreciated) discussion. I'm a little bit punchy because things are so easily taken the wrong way in a forum environment when they are not meant in an offensive manner. I'll be the first to admit that I'm no PLC expert either... I've had the good fortune of the opportunity to study hard and to design some machinery and control systems on my own. The hope is that we all keep learning as we go. For what it's worth, I can't spell worth a D--m either... if it weren't for spell check, I couldn't make a first impression for my life.
Thanks,
Tim
Edit: P.S. I have not used the 'Click' line from Automation Direct yet either, but I do love their gear and support. I'm a Big fan of the Stage version of RLL programming too.
Post Edited (Tim-M) : 12/22/2009 9:20:21 PM GMT