And...that is why, in 20 years, I have yet to do any project with a PC based control system. As a supervisory system yes, but not as the actual controller. Its either a PLC or a design specific controller (the one I developed was a machine controller, human interface with 4 buttons, 2x20LCD, 6 AC inputs, 6 relay outputs, based on the '877 chip) for anything that needs a robust system. >From: llile@SALTONUSA.COM >Reply-To: pic microcontroller discussion list >To: PICLIST@MITVMA.MIT.EDU >Subject: Re: PLC help >Date: Tue, 28 Jan 2003 10:40:16 -0600 > > > But as mentioned >before, its the software interface that makes it ladder logic, so that the >old timers can still program and debug I guess. Some packages are doing >it >more graphical, and then again the nextGen PLC's called SoftPLC that >simply >run on a standard PC with a bunch of I/O cards can be programmed in C. > >AARRGH. Taking a heavy duty industrial strength PLC program, >and making it run on a standard PC with internal interface cards, (IMHO) >is like taking a go-cart to the indy 500. Yeah, it will run around the >track, and when it works a PC will also run as fast as a PLC. But what >about when it hangs? Can it run in a 35C plant floor? At 98% humidity? >With dirty power, say an arc welder running next to it? With dust and >dirt flying around? When the power blinks out, will it reboot under >control? Yes you can solve all these issues, and by the time you have >spent the money and time to solve them, you could have bought a "real" PLC >and just bolted it to the wall. > >I keep having nightmares about projects where we shoehorned industrial >control or A/D equipment into PCs. THe end of the project is always this: > >1. Get the industrial controls and A/D outside of the PC box. All those >internal cards are nothing but headaches. That's what serial comms or >ethernet are for. > >2. Get something more reliable than a standard windows PC to run critical >processes. Even a refrigerator is a critical process. > >3. Think about embedded control, PLC or some other dedicated item that has >nothing to do except pay attention to our process. > >4. THEN port the output data to a PC so the operator can look at pretty >pictures of what was going on while his PC was down or paying attention to >something else. > >Just my 2c worth. > > >-- Lawrence Lile > > > > > >Micro Eng >Sent by: pic microcontroller discussion list >01/28/2003 09:45 AM >Please respond to pic microcontroller discussion list > > > To: PICLIST@MITVMA.MIT.EDU > cc: > Subject: Re: PLC help > > >whew...good. I was hoping you aren't just trying to make a better >mousetrap. > >I look at how a PLC works in the fashion that its an interprative >language, >in that each 'rung' is analyzed one at a time, so as the program grow, the >scan time begins to take effect. In other words, if you have a critical >function such as a sensor that must react immidiatly then you have to put >it >in several times thru the ladder rungs to ensure you capture the event. It >will simply scan from the first rung to the last rung and then start over. >A microcontroller can do something similar, in that you just run it in a >loop and each set of lines in the code could represent a rung, setting >flags >and turning on outputs. Timers could be in the ISR. But as mentioned >before, its the software interface that makes it ladder logic, so that the >old timers can still program and debug I guess. Some packages are doing >it >more graphical, and then again the nextGen PLC's called SoftPLC that >simply >run on a standard PC with a bunch of I/O cards can be programmed in C. > > > > > > > > >From: Orbit Communications > >Reply-To: pic microcontroller discussion list > >To: PICLIST@MITVMA.MIT.EDU > >Subject: Re: PLC help > >Date: Tue, 28 Jan 2003 07:03:22 +1100 > > > >I appreciate your comments but we are not wanting to develop a PLC. We >are > >developing a specific product that will enhance our Wireless connectivity > >products. It will incorporate many functions not available in a PLC. > > > >We are interested in the mechanics of how PLC logic is presented to the > >controller in a typical PLC but have no intention of reinventing an > >existing > >product. > > > >Kind Regards > > > >David Huisman (CEO) > >----------------------------------------------------------------------- > >ORBIT COMMUNICATIONS - Wireless Solutions that Work > >(Telemetry, Control, Monitoring, Security, HVAC ...) > > > >Website : http://www.orbitcoms.com > >PO Box 4474 Lakehaven > >NSW 2259, AUSTRALIA > >Phone: 61-2-4393-3627 > >Fax : 61-2-4393-3685 > >Mobile: 61-413-715-986 > >----- Original Message ----- > >From: "Micro Eng" > >To: > >Sent: Tuesday, January 28, 2003 1:07 AM > >Subject: Re: PLC help > > > > > > > First off...I've been doing PLC and ladder logic stuff for about 20 > >years. > > > Unless you have a buring desire to do this for fun, the product for a > >small > > > market might not be worth it, when you can buy all the pieces for what > >it > > > might cost to develop your own. For a specific use controller, which >is > > > what PIC's are great for, then it makes sense to build a board, etc >but > > > write the code in C or assembly since it is for target use. > > > > > > Now, for PLC applications, the only reason to write ladder logic is > >legacy. > > > In other words, thats the way its always been done, and the control > > > engineers understand it (maybe some don't relize its a throwback to >real > > > ladder logic of using relays and timers) so why mess with it? To get > >back > > > to the subject at hand, there is a company called Direct Automation >that > > > sells the stuff pretty darn cheap, because its thier brand, albiet it >it > > > probably a japanese remark, but you aren't paying the price for a > >Siemens > >or > > > AB unit. Of course, some outfits demand an AB unit, because of the >name > > > associated with it. I've developed using AB software, Rockwell, GE, > > > Siemens, TI and a few other off brand things, and they are all about >the > > > same. > > > > > > Just my .02 worth > > > > > > > > > > > > _________________________________________________________________ > > > Add photos to your messages with MSN 8. Get 2 months FREE*. > > > http://join.msn.com/?page=features/featuredemail > > > > > > -- > > > http://www.piclist.com hint: PICList Posts must start with ONE topic: > > > [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > > > > > > > > >-- > >http://www.piclist.com hint: PICList Posts must start with ONE topic: > >[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > >_________________________________________________________________ >The new MSN 8: advanced junk mail protection and 2 months FREE* >http://join.msn.com/?page=features/junkmail > >-- >http://www.piclist.com hint: The list server can filter out subtopics >(like ads or off topics) for you. See http://www.piclist.com/#topics > > > >-- >http://www.piclist.com hint: The list server can filter out subtopics >(like ads or off topics) for you. See http://www.piclist.com/#topics _________________________________________________________________ Help STOP SPAM with the new MSN 8 and get 2 months FREE* http://join.msn.com/?page=features/junkmail -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.