Post by thread:[EE] Industrial Hardened I/Os on PLCs

> What additional circuitry is on a PLC input that makes it "hardened" and > thereby more suitable for use in an industrial environment than a bare > microcontroller? Circuits vary, but some of the things they have are: Low impedance to prevent false triggering, plus good filtering. Over voltage and reverse voltage protection. Often optocoupling for isolation and decoupling of electrical noise. Defined threshold voltages. Also not to be overlooked - good debounce software in the micro. -- Brent Brown, Electronic Design Solutions 16 English Street, St Andrews, Hamilton 3200, New Zealand Ph: +64 7 849 0069 Fax: +64 7 849 0071 Cell: +64 27 433 4069 eMail: spam_OUTbrent.brownTakeThisOuTclear.net.nz

It's a long shot but ........ Has anyone seen interface cards/circuits for sale to provide this protection to a microcontroller? I'm thinking of a small multi-port add-in board that would provide a level of protection similar to what a typical PLC has. --Jeff Brent Brown wrote: > Circuits vary, but some of the things they have are: Low impedance to prevent false > triggering, plus good filtering. Over voltage and reverse voltage protection. Often > optocoupling for isolation and decoupling of electrical noise. Defined threshold > voltages. Also not to be overlooked - good debounce software in the micro. >

On 4 Feb 2008 at 20:44, Jeff Latta wrote: > It's a long shot but ........ > > Has anyone seen interface cards/circuits for sale to provide this > protection to a microcontroller? > I'm thinking of a small multi-port add-in board that would provide a > level of protection similar to what a typical PLC has. Opto 2 is a company that does modules like that I think. Pretty sure you can build a system using their I/O blocks with your own processor (or theirs). http://www.opto22.com/ -- Brent Brown, Electronic Design Solutions 16 English Street, St Andrews, Hamilton 3200, New Zealand Ph: +64 7 849 0069 Fax: +64 7 849 0071 Cell: +64 27 433 4069 eMail: .....brent.brownKILLspam@spam@clear.net.nz

On Feb 5, 2008 12:11 PM, Brent Brown <brent.brownKILLspamclear.net.nz> wrote: > On 4 Feb 2008 at 20:44, Jeff Latta wrote: > > It's a long shot but ........ > > > > Has anyone seen interface cards/circuits for sale to provide this > > protection to a microcontroller? > > I'm thinking of a small multi-port add-in board that would provide a > > level of protection similar to what a typical PLC has. > > Opto 22 is a company that does modules like that I think. Pretty sure > you can build a system using their I/O blocks with your own processor > (or theirs). > > http://www.opto22.com/ > Somehow it seems that in the end it will be cheaper and more reliable to buy a small PLC which include the I/O than to buy a separate I/O and then develop your own system. Xiaofan

Xiaofan Chen wrote: > Somehow it seems that in the end it will be cheaper and more reliable > to buy a small PLC which include the I/O than to buy a separate I/O > and then develop your own system. > > Xiaofan > Yeah, I might end up doing that. I've already invested a lot of time learning how to use microcontrollers with C . I was trying to avoid learning yet another programming language/environment, but if that's the way to go, so be it. The other option is to roll my own interface circuits. If I keep this up I'll be an EE soon. --Jeff

On Feb 5, 2008 2:19 PM, Jeff Latta <.....jlattaKILLspam.....alphasystems.ca> wrote: > Xiaofan Chen wrote: > > Somehow it seems that in the end it will be cheaper and more reliable > > to buy a small PLC which include the I/O than to buy a separate I/O > > and then develop your own system. > > > Yeah, I might end up doing that. I've already invested a lot of time > learning how to use microcontrollers with C . I was trying to avoid > learning yet another programming language/environment, but if that's the > way to go, so be it. The other option is to roll my own interface > circuits. If I keep this up I'll be an EE soon. Discrete input on the PLC is really not that difficult. Here is a good introduction book. So you can try to roll your own. For dedicated small system, it is justified to roll your own system if the quantity is high enough. http://www.eod.gvsu.edu/~jackh/books/plcs/ On the other hand, to learn the ladder program for PLC might give you some advantages as an EE as well. I learned ladder a long time ago on a small Omron PLC and somehow I need to use it again after so long. Xiaofan

> > Somehow it seems that in the end it will be cheaper and more reliable > to buy a small PLC which include the I/O than to buy a separate I/O > and then develop your own system. > > Xiaofan I needed relay outputs from a program running on a PC. After some discussions we ended up using a small, cheap PLC with RS232 interface and a simple ASCII protocol. As soon as the PLC gets a message from the PC it updates its ports. When no message is received within a certain time, all outputs are set to off (watchdog). The PC repeatedly sends the port status in the background. The program in the PLC was very short and simple. Much because the RS232 protocol could be set up very easy in the development environment for the PLC. /Ruben ============================== Ruben Jönsson AB Liros Electronic Box 9124, 200 39 Malmö, Sweden TEL INT +46 40142078 FAX INT +46 40947388 EraseMErubenspam_OUTTakeThisOuTpp.sbbs.se ==============================

The OPTO 22 family, and there are numerous other manufacturer's that make exact drop-in equivalents are available in many combinations of inputs including TTL, but I think one of the main advantages is, one of the weaker links is the interface to the outside world, i.e. the actual piece like motor that you are controlling, and the quick drop in a new piece without having to pull a whole board or unit with a whole bunch of connections. The nice little rectangular Opto's can be arranged in a nice grid, identified and make troubleshooting easy. They are very reliable, even used in jet aircraft by the dozens. I have a couple of times troubleshot the landing gear circuits on a friend's Mooney single engine, and then soldering in a replacement relay where an Opto could be replaced quickly with a screwdriver, and probably would have replaced the unit before even getting a meter out, or maybe wouldn't have even got the call for help. :) Xiaofan Chen wrote: {Quote hidden}> On Feb 5, 2008 12:11 PM, Brent Brown <brent.brownspam_OUTclear.net.nz> wrote: >> On 4 Feb 2008 at 20:44, Jeff Latta wrote: >>> It's a long shot but ........ >>> >>> Has anyone seen interface cards/circuits for sale to provide this >>> protection to a microcontroller? >>> I'm thinking of a small multi-port add-in board that would provide a >>> level of protection similar to what a typical PLC has. >> Opto 22 is a company that does modules like that I think. Pretty sure >> you can build a system using their I/O blocks with your own processor >> (or theirs). >> >> http://www.opto22.com/ >> > > Somehow it seems that in the end it will be cheaper and more reliable > to buy a small PLC which include the I/O than to buy a separate I/O > and then develop your own system. > > Xiaofan

> I have a couple of times troubleshot the landing gear > circuits on a friend's Mooney single > engine, and then soldering in a replacement relay Scary stuff. If they have failing relays 'several times" in the landing gear, whcih is bad enough, where else do they use them ? :-) :-(. Why do they fail? Why do they use relays? How many people have in-the-air problems with these? Does anyone die? Russell

What I remember it was the gear up circuit, the relay probably should have been rated a little higher amperage,but on airplanes you measure weight in ounces. Hadn't heard of getting gear down issues, and even if it wouldn't come down electrically, there was a manual backup, and then if not down, 99% of the time was a costly belly slide, which most of the time caused by pilot error. Apptech wrote: {Quote hidden}>> I have a couple of times troubleshot the landing gear >> circuits on a friend's Mooney single >> engine, and then soldering in a replacement relay > > Scary stuff. If they have failing relays 'several times" in > the landing gear, whcih is bad enough, where else do they > use them ? :-) :-(. > > Why do they fail? > Why do they use relays? > How many people have in-the-air problems with these? > Does anyone die? > > > > Russell >