PLC's control nuclear reactors. True, there are probably a ton of redundancy systems in a nuclear reactor, and there are many safety sub-systems that are in play, but they all tie in with PLC's. Mickey, I am trying to visualize a circumstance where a PLC is not "safe"...a situation where the program will not protect against fire. Thus far, every single circumstance that I can foresee can be handled by redundancy programmed into the PLC.
(1) sensors faulting (prevented by periodic automatic sensor tests)
(2) PLC shut down (make an alarm happen if PLC faults)
(3) Suppression actuators not functioning (monthly actuator checks, this may not seem ideal, but that's the same way the dedicated fire safety system works...there is no way to "test" them without physically turning them on and making sure water is coming out)
...you get the picture. I can't see a damaging event or failure that cannot be solved by redundancy. The fire system that we have is rebuilt, so it should be operational and "safe", but I didn't build the thing, so I can't work on it. Plus, electronic components fail. PLC, if you adhere to the ISA-88 standard, can be worked on by any competent ladder logic programmer. True, years of R&D went into these fire safety systems, but you have to think, they make a **** ton of money on these systems, for something that performs a relatively simple task. If they switched to PLC systems, and I can see why they would not want to do so, they wouldn't make NEARLY as much money. And money, my friend, is the whole reason they are in business. Code and licenses aside, I want something that WORKS, is PRACTICAL, and SERVICEABLE. I am cautious with this project, as you are the second person to tell me that this is not a job for a PLC (the other person was an engineer at the company that manufactures the spark detection sensors so I keep in mind he wants me to buy into his system) but so far no one has given me any reason why not. The PLC seems far superior in every way than a bunch of hardware that can fail at any point just as easily as the PLC. That being said I very much welcome and value ANYTHING anyone has to say on the subject. Perhaps I should start a new thread...