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| Mon, 28 Jul 97 10:57:45 -0400 |
| < Barry Ezell bce4k@virginia.edu> |
Could someone please explain the difference between how these two acronyms are used. In the literature and on the mail list, I have seen them both referred to for remote sites. Is there a difference in the level of 'intelligence' of a remote terminal unit and a programmed language controller? Is there a difference in the level of 'intelligence' between a programmed language controller and a PC at a remote site? I apologize if these questions seem elementary, but I have tried to follow comments back and forth over the past week and seem to be thouroughly confused. Thank you for your help. Also, thanks for all the input to the Scada model. My next task is to develop policies that speak to each of the identified points of risk. Afterwards, we will develop some multi objective optimization and determinew the best courses of action for Scada systems. Barry
| Mon, 28 Jul 1997 21:41:28 +0200 |
| < steinhoff@steinhoff.de> |
Yes, the programmed language controller can run application oriented different programs ... the RTU runs specialized firmware just for the IO job of the RTU. Well, the PC is much more flexible and 'intelligent' ;-) ... these are the best questions :-)
| Tue, 29 Jul 1997 08:26:29 +0800 |
| < John Bailey jbailey@cygnus.uwa.edu.au> |
PLCs
Again there is a difference in origin. The Programmable Logic Controller (PLC), sometimes called a Programmable Controller (PC), originated in the automotive industry in the late 1970s. They were a replacement for the relay logic used to control machinery. Their advantage over the relay logic were that they were programmable and that the program could be relatively easily changed; relay logic is hard wired, takes up a lot of space and is not easily changed. The ladder logic language which is still popular in PLC is the same as the ladder logic drawings use for relay logic wiring and hence is well understood by electricians.
PLC's were originally very large, expensive and were only suitable for large manufacturing plants. They were only capable of binary logic, no analogue, and were aimed a machine control. Early PLC's had minimal communications functionality beyond providing a port to plug in the programming terminal (no Personal Computers back then!). The operator interface was mostly provided by switches and lights hard wired to PLC I/O.
Eventually PLC's sprouted communications ports to allow allow them to talk to one another and to computer based operator interfaces. MODBUS
| Tue, 29 Jul 1997 10:27:14 +1000 |
| < ELEC_1 jeff.lloyd@mkysugar.com.au> |
No Message
| Tue, 29 Jul 1997 11:51:19 +0200 |
| < steinhoff@steinhoff.de> |
On Tue, 29 Jul 1997, ELEC_1 jeff.lloyd@mkysugar.com.au wrote: Oh yes ... don't leave out the PROFIBUS home page http://www.profibus.com for information about dumb RTUs. Information about the concept of intelligent RTUs are available at http://www.echelon.com. Armin Steinhoff http://www.steinhoff.de