SGPIGLF wrote:Hi to all,
I am new to Raspberry Pi ,control engineering and PLC System. I thought as long as the system is able to perform the function design for it will be good enough. Why is there a need to get Raspberry Pi to becomes PLC System?
Do understand from the discussion above on Safety which I agree but in many situations there are external circuits connected to raspberry pi that can be designed to incorporate the safety requirement I guess..... Correct me if I am wrong or enlighten me on it.
Hope to learn more about all the experts here. Thanks.
Hmm... An interesting question. I bet everyone will have their own answer to it
If you're asking as long as the Pi can turn on and sense digital signals and measure and source analog signals (which is 95% of what a PLC does) then why do we need to make it a full blown PLC since it's already doing everything a PLC does.
For me safety is a non-issue. There are great SCADA applications for the Raspberry pi without trying to turn it into an industrial PLC. By the time I make a Raspberry Pi into an industrial safe PLC device I would have been better off purchasing a cheap PLC off eBay. Instead, I think the real benefit for making a PLC Raspberry pi is for the educational aspects. To be able to take the Pi plus a digital and analog I/O card and be able to control that card not with java or python or C, but to be able to control it with PLC logic would be an amazingly beneficial thing.
For example, I just purchased an old Allen-Bradley SLC 5/02 off eBay, the PLC plus the power supply, the rack to hold it, a DC input card, DC output card, AC input card, AC output card, and an analog input card all cost me about $200. That's not too bad, but then I realized that the only way to communicate with it is to purchase a very expensive Allen-Bradley converter to talk on Datahighway, and then I can't edit the program online, or use floating point math. To get those features would cost me another $100. So for $300 I could have outdated technology that required a serial port to program (though in its defense, it would give me 32 digital inputs, 32 digital outputs and 4 analog inputs plus a more or less real time clock).
That's just WAY too expensive to use in a class room environment. I can't even get my company, a PLC programming company, to purchase a training PLC for new employees to learn on for that price! But a $50 solution that used the Pi and gave just a handful of electically isolated I/O and maybe an ADC with a could analog inputs? It wouldn't be much but it would be more than enough to teach new employees the basics and would be almost 3 times less than the last useless college book I bought!