My knowledge base is in electro-mechanical devices and hence I currently providing training to Industry in the areas of Pneumatics, Hydraulics, PLC's and associated technologies.
I am thinking of branching out my training services into other related areas and so I am setting about doing a little research as to what devices or kinds of technology are now the most popular & indeed as to what devices are going to be the up and coming norms in technology for the future. Perhaps devices like variable speed drives or proportional hydraulics?
I am wondering has anybody got an opinion on what is or will be in demand in this area of electro-mechanical engineering. I'm particularly interested in packages like PLC's, Logic Blocks, Variable Speed Drives etc as they are small and relatively cheap and simple to make related training devices and accompanying notes etc.
Dear Declan, PLCs are not considered electromechanical devices, but computers of industrial strength.A very interesting apllication of hydraulics is the german diesel-hydraulic train locomotive.Also, a very common electromechanical device is the old-fashioned timer of washing machines and dishwashers.Most devices now tend to be electronic, timers, washing-machine timers.The only thing that will stay e-m is the relay, there is no substitute for it.Variable speed control drives are also electronic, AFAIK they have no moving parts except perhaps a fan.
-- Tzortzakakis Dimitrios major in electrical engineering, freelance electrician FH von Iraklion-Kreta, freiberuflicher Elektriker dimtzort AT otenet DOT gr Ï "Declan McEvoy" Ýãñáøå óôï ìÞíõìá news:bti2e.50537$ snipped-for-privacy@news.indigo.ie...
On Sat, 09 Jul 2005 06:10:31 -0500, Steve Cothran proclaimed to the world:
And I agree that there is a place for contacts. I would not think of eliminating a circuit breaker or contactor as a safety device in a circuit, but......think of all the applications where the triac has replace the poor overworked contactor or even made possible high speed switching. Don't read more into what I said than I did. Triac and transistors are the solid state equilivelent of the E-M switch. Both have their pluses and minuses. There are applications where I would much rather have ten relays in my design if it would eliminate the need for a PLC and I have done this. At the same time there are application where I would be hard pressed to do what was needed without a PLC. I've seen logic written that takes 20 pages that I rewrote in two lines because the guy writing it appeared to have very little imagination and I have seen code that blew me away. The key to good engineering is to use all that is available, not just what is new and sexy.
Be well,
HoP
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Your initial remark implied that you would. When statements like that are allowed to pass unchallenged, onlookers may be deceived. I'm probably overly sensitive about that.
I can only guess what that sentence means. When a sentence is unambiguous, I assume it's either a joke or you mean what you write.
On Sat, 09 Jul 2005 18:00:42 -0400, Jerry Avins proclaimed to the world:
I find it is very difficult not to be ambiguous without putting in more effort that I am willing for each sentence. I try but never reach that goal. I apologize.
I am also new here and am used to being on a support group where people are talking about things that are indeed muddy. Mental health is not cut and dried. Again I will try to make the transition as smooth as possible.
Be well,
HoP
The preceding message represents personal opinions and/or advice that may prove incorrect or harmful. But then maybe not. Feel free to disregard.
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Me too. Except you can now buy a plc for about what 10 relays and sockets cost and it has the relays (or triacs/xistors) in them already.
I've seen logic written that takes 20 pages that I
Naw, he was programming using TIP. (To Impress Peons). I'm with you, I see it every day.
On the other hand, I once got called into an engineer's office for using "un-needed complex programming" on a project. I had used a shift register to keep track of parts on a rotary table.
The day I learned to program with ladder diagrams, I had gotten called in by the mechanical group (I was part of an instrumentation and circuit-design shop that acted as consultants) to design a hardware shift register that could be set, advanced, and read by a TI PLC controlling a turntable bearing parts. It was only a package of flip-flops and another of gates, and I had it running in under an hour. When I brought it over, I asked why it wasn't programmed in the PLC. They told me that, according to the TI field engineer and confirmed by his boss, a shift register couldn't be built in ladder logic. The mantra was "You can do everything, and only those things, that you can do with relays."* I borrowed a small PLC with manual that people used for getting familiar, and learned how it worked. The rungs of the ladder were evaluated sequentially, so proper organization can make a race impossible. I programmed the shift register by the time the mech boys got back from lunch and gave it to them. The next month, the circuit was in TI's application magazine without attribution or thanks.
Jerry _______________________________________________
I can build a shift register with relays, but only by cheating; slower relays here, faster ones there; otherwise, race. A parlor trick not suited for production.
On Sat, 09 Jul 2005 21:29:11 -0400, Jerry Avins proclaimed to the world:
Jerry, the first true PLC I worked with was an Atcom. I don't think they make PLC now at all, but the idea of programming in ladder logic was not really though of then. Ladder logic programming came about because the things didn't sell because nobody knew how to program using their assembler which was very similar to basic except it overcame the problems of real time execution. I had been playing with basic programming for years on first the Apple II and then the first PCs. You could do just about anything. Ladder logic was something pretty strange to me. At that time I had not designed anything in ladder logic, but used others drawings to troubleshoot existing pre-PLC machines. I ate up the Atcom unit. I could do anything with it. No one else could though and in a year or two the Atcom 64 was history and Ladder Logic was selling like the next great thing. It wasn't great. It was an assembly program that forced the constraints of the old world of putting relays together to for basic logic functions and it came about because there was an established world of engineers that understood how to write this stuff. I was a salesman/tech rep then and I could sell the idea of using PLCs to the engineers with ladder logic. The guys that taught in school could understand ladder logic and the transition for them to teach PLC programming became a reasonable task.
The last I worked with AB, they had started the Advanced Programming Software which was in essence going back to what Atcom had to start out with. The differences is that AB is in essence now trying to use the free form basic programming style to write logic, then convert it back into the highly structured ladder logic of old. It does not work well. Square pegs, round holes.
Now my version of things is about five years dated. I hope things have changed for the better, but from what I can tell so far it has not. What I saw from the times that I was asked to teach courses back then, it was very rare for any student to be able to make the leap beyond the strictures of ladder logic programming but then the generation of guys that had experience in computer programming had not gotten into the schools. I was either considered a wizards wizard or a kook by most controls teachers. There just were not very many people around that knew both computers and controls. Now I feel like a fossil. I have to commend you for making the leap beyond the false strictures of RLL.
What Tim does with embedded controls is a step beyond this and works the basic area that I feel everyone should be at, but this will never be because things get designed and built so that the most people can use them. That means building on top of what was and that is never the most compact and efficient way to do things.
I'm not for sure why I wrote all this. It is good to have someone to tell this to that understands for one. It has always been an irritant to me that things are not perfect. I am an idealist and that is my downfall most of the time. I insist on trying to make the world do things the way I see as the right way and it never does.
Be well,
HoP
The preceding message represents personal opinions and/or advice that may prove incorrect or harmful. But then maybe not. Feel free to disregard.
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Your version of things is more like 25 years dated! I went through the same thing you did in about 1978!!
You are correct, ladder logic was designed so that PLCs could be used and understood by people who don't have formal training in programming, and that is exactly why PLCs are successful today. Now, people with formal programming experience look askance at ladder logic, and tell me how much easier everything is in C++, until I ask them to make edits in a running processor, or change data values change as the machine runs, etc.etc.
You are also correct that ladder logic has its limitations, and that is why all except lowest end PLCs now offer multiple programming languages. AB currently offers ladder, sequential function chart, function block and structured text (a kissing cousin of PASCAL.) If ladder logic doesn't work for you, there are other choices. In the specific case of the AB product, these are true languages, they are not pretty faces put in front of ladder logic.
And really, what is so terrible about ladder? All it is is Visual Boolean! For fiddling with individual bits, why not?
However, and this is probably your real point, and awful lot of people learn a little bit of ladder and never go any further. It is true that you can do almost anything in ladder, but unless you are willing to learn past the point of timers and counters it is usually the most difficult possible way. Yes, you can do a shift register with coils and contacts, but why not LEARN the shift instructions!
What is happening in the PLC industry today is interesting. Basically, the worlds of the PC, the PLC and the DCS are coming together, and the new products combine important features of each. Communications and networking is now the BASIS of PLC architecture, rather than an afterthought. User-defined data structures and techniques have replaced the old data table designs. Use of OPC data servers has made PLCs interoperable with PCs.
Point is, if you want to do anything important with PLCs today, ladder logic is just a tiny part of the picture, rather than the WHOLE picture as it was
25-30 years ago. If you understand modern PC programming and architecture the new PLCs will be very easy for you. If you understand nothing past coils and contacts you will NEVER get anywhere with the new generation of PLCs.
On Sun, 10 Jul 2005 11:10:18 -0400, "BFoelsch" proclaimed to the world:
I mean that the end of the story dates back five years because I have not worked in that long because of sickness. The tale does start 25 years ago indeed.
Changing during a run is a big plus.
Well I think you have not caught the reason why I am here, taking the time to share and learn. I have been out of the field for five years mostly and want to learn where the industry has moved too. I would have to check but I think that the version of APS I have from AB is the original. You are answering questions I have about where they have good without me having to buy a new version and finding out, only to be disappointed.
Nothing, but it has it's limits and when that was all there was and this did not have to be true, that was terrible. For some basic stuff it is great. I once needed to do something quick and cheap for a pump station. The designers had forgotten to include any pump logic like alternations and turning the damn things on and off according to pressure. They supplied the sensors, but nothing else. I had been hired to commission the station and it was way back in the sticks. I happened to have a relay block with an embedded controller that I was able to program on site that day that did everything I needed. It only had four outputs and two inputs, but that is all I needed. For this ladder works just fine.
Yes it is, and when I got sick it was just starting. In the past I have spent a lot of time being frustrated at waiting for the industry to adopt what I thought should have been obvious. The large majority of my business has been taking care of something someone else designed. My business is in a rural area too. I don't choose which PLC I work on. I got really tired of seeing all my profit go towards buying the programmers and software necessary to work on all the different manufactures versions of the same thing. I was really frustrated trying to integrated two different systems. Or five. I was frustrated having to be the one to here the end users complain about these same things. I was bitching about the stupid idea of putting all the controls into one box at a wastewater plant and watching that box fry in the middle of the night as the entire plant goes down and goes into flood mode. DCS you say? I was screaming about this at the seminars back before the term was coined.
And I do understand the whole picture. My point is that it should have started out that way. It was obvious to me then. It was obvious to me back when each programmer was writing his own bubble sort sub that it should be done right with the minimal amount of code and then set as the standard. It was obvious that the OS on PCs need not take 552 megs of memory. It was also obvious that Microsoft was making it's customers pay for sloppy programming.
But then I am, as I said, an idealist at heart and have to work hard to be pragmatic in a less than ideal world. It is rare that I get to say the things I am saying now to someone that understands the first bit. I'm not knocking individuals but I do have a problem with some of the industries short sightedness. I can't change what has happened. I can talk about it and maybe things will change some in the future. It's said that history repeats itself. I've seen this many times. Coming up the way I have in the industry I get to see what a lot of controls designers do not. I see the problems maintaining the systems after the plant is built and commissioned. I'm the guy that is hired to straighten out the mess that is left after a lot of engineering firms are fired from the job. I'm also the guy that get's screwed out of being paid because the customer then wants that engineering firm to pay for me fixing there shortsightedness. It's seldom that this happens. I get stuck in the middle.
I also am tired of seeing a lot work on my part go for nothing because I had to go back and learn something like ladder logic versions of programming PLCs that I thought was backward thinking to start out with, then only to see that abandoned for the "new" way which is actually a poorer version of what I was advocating in the first place. [insert big sigh here]
Intellectually I understand these things and know that to do well I have to work with the way things are and find a way to make that work in my favor. This is why I am excited about finding sci.engr.control. I see this place as a way for me to better understand what is happening and take control of that knowledge. I really do not know enough of the history of this place. That will come. I can see that there are people here that know more about certain areas of the industry than I do. Hooray! I am opinionated but that opinion changes and I'm hoping that you will be a part of changing it. I also hope that I will add something to the knowledge and opinion of everyone here. If that happens then we all gain.
I'll be doing my part of learning about what is new and improved in the controls industry since I dropped out. Your reply has helped me towards that goal and I thank you. I really do not disagree with anything you said other than perhaps you are reading more into what I said that was there.
Be well,
HoP
The preceding message represents personal opinions and/or advice that may prove incorrect or harmful. But then maybe not. Feel free to disregard.
------- Words have no Warranty ------ ------- No View without Merit ------
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