PLC to PLC Communications

I am studying instrumentation at college, and am in the first year of my HNC. I have a PLC assignment from college and have found myself pretty stuck with one of the questions. After a quick google I found this page and from the post I've been reading its full of useful knowledge and hopefuly someone who will be able to help me with my question.

The question is:

'Consider two types of communications links with PLCs. PLC to PLC and PLC to LAN. Draw a scretch with relevant modules from manufacturers how they would be implimented on network systems.'

I am unsure if my problem with the question is just the basic comprehension of it but I am hoping that someone on this forum will be able to help me out or point me in the right idea.

Any reaplies will be greatly appreciated.

Thanks

s7-300 <---Profibus---> s7-300
CP343-1
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L
A
N
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PCs

I hope you ment this

Thanks very much for the quick reply. But the means very little to me. I am a total novice to PLCs. It would be hugely appreciated if you could maybe explain it simply in lamer terms please? It would be a real help

Also does the above apply generically to most PLCs?

The main idea is that PLCs should communicate together on industrial level and they should communicate on a plant level ( to make charts graphs etc ).
How many communication ports PLC has, so many communications can be established.
So communication on level PLC - PLC is usally used for machines consisting of more parts, where one part is waiting when the second part will be ready to reiceve a product for further processes.Communication protocols (the language of communication) depends on producer of the PLC. Siemens (MPI,Profibus),AB(sercos,devicenet) ... or free Modbus, Canopen.

The other level is to transfer data upper ( number of produced parts, errors etc ... ) Its PLC - PC communication (because PC can make a graph, export to excel or save it on the CD )

So if your PLC is Siemens it usualy has Profibus connector for Profibus communication. So you have 2 PLCs = 2 ports and "simsalabim" you can connect it together. For the necht communication is neccesary to have another port for communication. This one will be different because you are trying to connect to LAN. So you will buy Ethernet card CP343-1 from Siemens, include it to the machine and plug Ethernet cable to PLC and to computer ...

Thanks very much! Much appreciated, think Ive got it now.

But also any other posts / more info will be appreciated too!

from PLC to LAN usually requires some form of ethernet. The rub come in when trying to "decode" the data. That is when soemthing called OPC comes in. Goggle OPC for more info.

PLC to PLC has lots and lots of flavors. Different with every PLC manufacter. Google Key words DeviceNet, Controlnet, Profibus, Profinet, Modbus The Devicenet and Controlnet are Allen Bradley protocals, Profibus, Profinet are Siemens. Modbus is the gandpa of them all and is generally what is called an open protocal.

Important thing to understand and is probably what your teacher is looking for is that hardware is only part of design. Lots of times you have to understand how the data is transfered to really understand they system.

To create a PLC to PC network, first pick what brand and model of PLC you want to use. Note I said brand and model. Inside of each manufactor of PLC's there are different models. Each model allows only certain communication protocals to be used.
So everything has to match.

A PLC to PC network starts the same way. Figure out which brand/model PLC you want to use. The PC does not have to be brand specific but be able to run the OPC software you select. The OPC does the translation of the PLC data for you.

Just for the record nothing can bring a control system to its knees faster than a poorly designed network. You have a really good project to work on there.