I want to teach others.

Hi all,
I am in the process of really learning PLCs and understanding everything about them so I can teach others about them at work. I was answering coworker’s questions about an Allen Bradley Slc500. They were asking a lot of questions about inputs and outputs. I told them that a bit is either on or off (1 or 0). A nibble is 4 bits, a byte is 8 bits and a word can be 16 bits, 32 bits or 64 bits. They had a blank look on their faces, when I told them about how a word is used and how it can be moved. I would have told them to look on line or get a book to look this information up, but my boss wants me to teach him and some other workers on my crew about PLCs. He is a good supervisor but knows very little about PLCs. My question is; what is an easy way to explain to him and other workers on my crew what a word is and how it works in a PLC? Any easy explanations would be greatly appreciated. Thank you all for your help in advance.

Sincerely:
Maintenance Man.

I want to teach others

Also I was talking to them about input and output modules with 8 bit, 16 bit etc. Maybe I over explain things, so a simple example for teaching this would also be greatly appreciated. Thank you all.

Sincerely:
Maintenance Man:

I started off with the information at the top of this web page.

Dan Bentler

Keep it simple at first. Just tell them that a word is where a value gets stored.

Point to a switch/button and explain that when the switch is toggled a single bit is shows up as either a 1 or a 0. Point to an indicator light and explain that when the PLC sends a 1 or a 0 the light turns on and off.

Then point to a potentiometer and explain that we need more than just a single bit for this since it is a variable input. Instead we need somewhere to store a value (or number). When the pot is cranked all the way down the value is very small and when the pot is cranked all the way up the value is very large.

That is a relatively easy starting point.

OG

Thank you Operaghost

Thank you Operaghost, that is a very easy way to explain it to them. I should have made my explanation easy like that. I guess I tried to use too much detail when I should have used K.I.S.S.

If you have a running SLC or micrologix show them view of the data table for integers (N7)or binary files (b3)
View it in binary and decimal (if not sure ask here) Then as you change bits or values have a look at the opposite view change. MAKE SURE IT IS NOT A WORD IN USE IN THE PROGRAM.
Regards Alan Case

Greetings Maintenance Man ...

let's take a look at what you started off with ...

I told them that a bit is either on or off (1 or 0). A nibble is 4 bits, a byte is 8 bits and a word can be 16 bits, 32 bits or 64 bits.

Click to expand...

let's assume for the moment that everything quoted above is absolutely correct ... the question I'd like to ask is this:

how much of that material does a maintenance technician actually need to know in order to troubleshoot a PLC-controlled system? ...

here's my point ... the "Boot Camp" classes that I teach are targeted directly at what a technician needs to know in order to troubleshoot a malfunctioning PLC-controlled system – and to get the system back in operation again ... I assume that your teaching objectives are along the same lines ... with that in mind, here's what your statement above boils down to:

I told them that a bit is either 1 or 0.

Click to expand...

now THAT part is solid useful information ... the rest could easily be considered "fluff" or "filler" ... here's where I'm going with this:

more than 99% of my students have already been to "someone else's" PLC training ... the only reason that they come to me is that they didn't get what they needed in those earlier classes ... that's because a LOT (if not MOST) of the material covered in those other classes boils down to just "fluff" or "filler" ... for example: the four students in last week's class were amazed that we didn't start out with the traditional HEX/binary/octal numbering system conversions that had been crammed down their throats in all of their earlier classes ... instead of killing a day or two with stuff like that, my students begin working "hands-on" entering a sample program within ten minutes of the class starting time ... the boring numbering conversions (and other similar subjects) are on a "need to know" basis in my classes ... specifically, we're not going to mention that material until we NEED that material ... and then we're not going to spend half of a mind-numbing day covering it ... instead I'll just spend 60 seconds or so explaining how to use the "scientific view" of the Windows Calculator to make the conversions automatically ... (for Pete's sake, folks - we're sitting in front of a COMPUTER here ... how on Earth can you justify spending HOURS of classroom time on learning how to manually convert from HEX to binary?) ...

some other examples of "filler" and "fluff" are the model numbers of the Motorola or Zenith chips used in the processor ... who the heck cares? ... that type of material has NOTHING/ZERO/ZIP/NADA to do with what a maintenance technician needs to know in order to get the pump running again ... yet when my students show me the textbooks they used in their previous classes, there's usually page after page of totally useless information in there – and the instructors took a LOT of time covering it ... (so how much time was left for the GOOD stuff?) ...

so here's my recommendation ...

first go through the stuff that you KNOW – and pick out the pieces that are NEEDED ... then cover that stuff first ... later (once a solid USEFUL foundation has been laid) IF (that's a big IF) you want cover other things, by all means do so ...

let me make sure that I've made my point ... the key is to not start out by filling up the students' heads with "raw information" – but instead to give them a SOLUTION to a specific PROBLEM ... if you'll do it this way, then the students will see the "connection" (here's a PROBLEM – here's the SOLUTION to that problem) and they'll appreciate its significance – and (most important) they'll REMEMBER the material when they need it in the future ... that's the way that the human mind is "wired" ... it's amazing to me that more instructors never seem to "get" that particular point ...

although I hate to say it, in many ways teaching PLCs is a lot like teaching a teenage girl how to drive a car ... for the first lesson (usually on the far side of a K-Mart parking lot) the little sweetheart has only TWO questions in her mind: (1) how do I make it go where I want? and (2) how do I make it go faster? ... so ... the ONLY "first day" topics you'll have any lasting success with are (1) "steering wheel" and (2) "gas pedal" ... topics like "turn signals" and "blind spots" and even "brake pedal" just get filtered out ...

key point: YOU (the instructor) might know what's important, but unless the STUDENT thinks it's important, then there's little or no chance of making the material "stick" ... the key to success is making the student realize the importance of each new piece of material ... that's where my PROBLEM/SOLUTION approach comes in ... I recommend that you try something along those lines – it works VERY WELL for me ...

now then, if you haven't already seen the YouTube video lessons on the "Sample Lessons" page of my website, I'd recommend that you watch them (ALL of them) IN ORDER and see if that helps you nail down the basics ... but please realize that those 11 videos are just PREVIEW of some of the material that I cover on Monday morning of a five-day class ... in other words, it's just a "start" – but it's a very important start ... the main point brought out in those videos is that MOST people who work with (and who teach) PLCs have quite a few misconceptions and misunderstandings about what actually goes on under the hood – and about how to interpret the indications on the computer screen ...

so ... make sure that you KNOW your material, and that you can absolutely PROVE that what you're teaching is correct ... my own personal rule is this: if I can't PROVE it, then I don't teach it ...

if you're interested in more about my personal teaching approach, there's a LOT of detailed information available for free on my website ... the "Boot Camp Experience" page is a good place to start ...

I hope that this helps ...

It is a noble desire to teach but, particularly with regard to automation, you ought to figure on working in the field for 10 years and getting accomplished there before attempting to teach. Real teaching is more about the exceptions than it is about the rules and I know of no other way to gain that knowledge.

DickDV is absolutely right – but I've got a hunch that Maintenance Man isn't really planning to hang out his shingle for a business in PLC training ... (at least no time soon) ... instead I think that he's mostly interested in how to answer basic "how-did-you-do-that?" type questions from his coworkers ... my post above was written along those lines - and hopefully it will give some useful guidance ...

Maintenance Man said:

Thank you leitmotif for your reply. I also started with the information at the top of this website. I wish others I work with would do the same to learn about PLCs. I just need to be simpler in explaining PLCs to others who are starting out.

Click to expand...

I agree with both Ron and Dick DV. The basic thrust of in house training for industrial electricians would be how to get the machine controlled by PLC running again. As an example most (?) industry will not let electricians do any program writing and in worst case one where I worked did not have the computer support much less manuals.

So why teach them all about bytes hex and all the programming stuff if you never let them into the program?

I also think that you will have them self select for two catagories - those who want to know just enough to get machine running again ie which fuse to replace or if a little more advanced which input light correlates to which safety switch.
For the basic guys a list of which lites correlate to what switch is invaluable - same idea for outputs. A basic ladder diagram of logic for them may be helpful. This should get them thru 50 to 60% (??) of the troubleshooting needs.

For the hot runner guys that basic knowledge coupled with letting them see what the computer program looks like will be appropriate as the next step.

For the really hot runners a laptop in the shop a PLC and a bunch of sensors and lite bulbs should keep them occupied especially if you let them write their own programs and make things run under test conditions.

Dan Bentler

Thank you all.

Thank you all for the great help. Ron is correct about me not wanting to be an instructor; I am just trying to help the other 4 people including my supervisor learn something about PLCs. I agree with you all that I do not need to let them know the workings of the PLC unless they understand how to get a machine running by understanding inputs and outputs. I enjoy working with PLCs and have spent many hours working with the Logix Pro from the learning pit and going over the books from this web site. I have also attended some PLC classes from Allen Bradley. This August I will be taking the Mechtronics Engineering course for automation. All I can do is pass the PLC ball to my coworkers and it is up to them to drop it or run with it. I will show them the important things to get a machine going then if they show interest, I will teach them more. I appreciate you all taking time from your busy schedule to answer my post. Again thank you all very much.
Sincerely:
Maintenance Man.