PLC Characteristics

[kernal_rob]

I just wanted to know the difference between Unitary, Modular and Rack Mounted PLC'S. Cheers

 

[Steve Bailey]

And so does every other HNC wannabee. But people in the real world who actually use PLCs as components in working control systems don't care about such semantic silliness.

 

[PLucas]

I just wanted to know the difference between Unitary, Modular and Rack Mounted PLC'S. Cheers

The infamous HNC question. This question comes up every year, do a search of this site and I am sure you will find an answer to your question.

Paul

 

[jimbo3123]

HNC?

 

[Steve Bailey]

HNC is Higher National Certification, or similar words. It's a British standard. That particular question has been on the test for several years, and we can always count on some student to post it here fairly regularly.

[soapbox]
For those who might think that standardized tests are a panacea for all that ails the educational system here in the USA, let this serve as a cautionary note. Who gets to decide what questions are asked on the test?
[/soapbox]

 

[93lt1]

That particular question has been on the test for several years, and we can always count on some student to post it here fairly regularly.

As well as:

1. The carwash program
2. The parking lot/garage gates program
3. The One-button toggle program
4. The stoplight program

There are many others, and variations of these, that really show up on the board, in full force, about this time of year.

 

[kernal_rob]

Just a note to all those people who said that this HNC question comes up every at this time all this people who can judge somebody who asks one question. Im not even doing my HNC as i have already done it years ago and i didnt take the PLCS unit. I have justed started learning PLCS and it was something i heard and i was curious as to what it was. So this is a message to all those JUDGEMENTAL People.

 

[Steve Bailey]

Well kernal_rob, don't think of us as being judgemental of YOU. Think of it as being judgemental of the people who seem to think that this information is so vital to understanding PLCs that they see fit to keep it on the test year after year.

 

[jimtech67]

Can you help me

I have to program my carwash that exits into a plc programmed parking lot with a single button operation gate to a traffic light to exits the lot.


Just kidding

GO JETS
As you see I have to laugh about something

 

[kernal_rob]

Message To Steve Bailey appology's to you Steve if you werent being judgemental. I kind of understand if the same question is asked quiet frequantly it must get annoying.

 

[rsdoran]

I am going to answer the question

What was it again?

OH what is Unitary...that is for me an term that WAS NEVER used but applies to FIXED ( what some of us call "bricks") PLC..like an AB SLC 500 L40. Siemens S7-200. AD DL05 etc

Modular: That is a system that is in between fixed (brick/unitary) and rack type. It uses a rack type system but CPU and housing is built in..Allen Bradley SLC 5/01, some GE Fanuc 90/30, etc.

Rack: That is a system that use uses a RACK that power supplies, CPU's, I/O and remote adapters are used in.

Each system has its use, Modular usually offers more options than unitary...rack usually offers more options than modular.Options like number of I/O count, analog, and communication etc.

BTW....I dont buy the guilt trip attempt by reversing the scenario. This was a blatant HNC question which obtained blatant answers...and by some that have done HNC. Its my belief that a skilled person investigating any subject will find answers to scholastic questions on their own...even if its just doing a search on a site like this.

 

[plc.doctor]

I know this is a little late in the thread to post this BUT here goes.
There is a search function on this message board that allows one to search for multiple terms. I did a search for "unitary modular rack" and got 7 hits including this one. The best answer to the question is in this thread because it uses visual aids with the answer. This message board has a wealth of information and has been a valuable source of tips.

 

[Vetteboy]

Actually...

I don't know if this specific to Allen-Bradley but, a rack and a chassis are two different things. Depending upon the type of addressing you are using (PLC5), you can have more than one "rack" in a Chassis.

See page 4-8 if you want more detail:

http://www.ab.com/manuals/cp/17856512.pdf

 

[Rick Densing]

The Unitary term is what seemed the giveaway. The only time most of us has seen the term is when an HNC student posts it. It seems to be a term made up by acedemics and is not used in the real world.

BTW, being judgmental is not always a bad thing...