PLC TYPES

[Guest dipankar555]

I am new to PLC things. Please enlighten me about difference(s) among various types of PLCs available like Single Processor, Dual redundant, TMR, QMR etc? Regards.

[Guest]

Greetings dipankar555, I have been working with PLCs for about 15 years ... to be honest with you, I have no idea how to define the terms you are using ... are these taken from some book or website that you’ve been reading? ... or are they assignments in a PLC course that you’re taking? ... can you give us some more information and tell us in what context the terms were used? ... maybe then we could help ... and yes, I know that sounds backwards ... after all you came to us for answers ... all I’m giving you is more questions ... I’m sorry ... and maybe someone else will come along with the answers later ... in the meantime ... you said that you are new to PLCs ... my suggestion is that you start by studying basic topics such as how to interpret ladder logic programs ... and understanding I/O wiring ... and then work on communications, etc. ... along the way you’ll undoubtedly learn more and more about how to write PLC programs (assuming that you’re interested in that field) ... sorry that I couldn’t be more help ... hopefully someone else will know more ... and welcome to the forum ... best regards, Ron

[Steve Bailey 118]

Just learning PLCs and you're starting out on redundant systems. You've got your work cut out for you. The systems you mentioned are different versions of redundancy strategies. Redundant control vastly increases the cost and complexity of a control system. It's justified in applications where the cost of downtime is high enough to warrant that additional overhead. When I say "cost of downtime", I'm not just talking about money. The cost is also measured in terms of the impact on human health and safety or environmental impact.

[Chris Elston 79]

To touch on this point more, applications would include things like roller coasters. The Raptor Roller Coaster at Cedar Point has four Allen Bradley PLC5 systems. Two PLCs monitor safety circuits in a redunant fashion, the other two PLCs monitor train position and location on the track in a redunant fashion. Quite interesting and a very well applied application for redunant PLCs.

[Crossbow 296]

I've seen a few roller coasters with redundant Modicon Quantum PLCs.... not that this has any bearing on anything....

[santiago 0]

for someone just starting with PLC's you will have to consider just the important things , today all major brand PLC's are for saying the least very good , I usually work with most of them , even some new cheap brands surprise me for how good they are and how good their software is. The important things to consider are : 1. if you program for clients , what brand most clients will prefer , in Europe most will use Siemens , mostly because factory standards , thats the PLC that most technicians know, so you have to supply with what they prefer, or maybe they have a net and SCADA to connect to. 2. do you prefer Ladder programming or function block? most people that grow on either are not so comfortable with the other. 3. Do you have a good supplier of parts , cards , CPU's , would you get them today? This is very important , in Industry downtime is expensive 4. price , for most applications the cheap ones will do too, this days reliability is on most , I have found out that some Korean or Taiwan PLC's are as reliable as Siemens , Omron , Modicon, and sometime with very surprising exellent softwares and capabilities, and I am talking about systems of 200 I/O +.