How to verify PLC networks.

ivannn · Jul 31, 2014

So I have no experience with PLCs and am currently doing an internship in a manufacturing facility where they are highly used. My current task is to verify networks and learn how the machines communicate with each other. I have no clue how to get started. I have RSLogix 5000 installed and can see all the programs and PLC's. Any suggestions of how to get started? I need make a diagram of how all machines communicate with one another through the PLCs. I appreciate all the help I can get. Thanks!

Dravik · Jul 31, 2014

Have someone help you grab the system prints.
There *should* be an interconnection diagram for each system.

From inside of Rs5000, you can look at each rack and find the communication modules(ie, things like 1756-ENBT, 1756-DHRIO, etc) and see what child/parent relationships they have.

You could also open up any SCADA/HMI programs and look for how they are setup to communicate to the PLCs. Directly? Through a gateway of some sort? Etc.

ivannn · Jul 31, 2014

Thanks Dravik. I will start there. Can you explain what you mean by child/parent relationships?

widelto · Jul 31, 2014

Child/Parent is the same as master/salve, one commands the others receive orders.

ivannn · Jul 31, 2014

yeah...that was a dumb question.

THANKS!

Dravik · Jul 31, 2014

^ Yeah same difference really.

In Rs5000 you'll have a backplane listed under your I/O config.

For each communication module, you should be able to 'drill down' using the +- signs to the left of the module. This will show you what devices the PLC is setup to talk to.
If you are doing a MSG instruction for example, The PLC executing the MSG instruction should have the target listed in its I/O config somewhere.(Note the 'should', You can hardcode addresses in some MSG instructions)

Dravik · Jul 31, 2014

In the Rs5000 help, you'll want to lookup
MSG instructions
Produced/Consumed Tags

You could also be dealing w/ Profibus, Modbus, DH+, RS232/RS485, etc.

and keep in mind, SCADAs and HMIs won't be listed in the PLC program necessarly. You'll have to verify those seperately.

ivannn · Jul 31, 2014

Is the Who Active tree diagram the only thing that shows which modules are connected to which? How can you tell which module is receiving and which is sending info/commands?

Dravik · Jul 31, 2014

Who Active only shows what your computer is configured to talk to/see.(It is using the local RsLinx service to do this)

Inside of each PLC program, You'll need to make a list of the communication modules and what they are configured as.

List out all the children then cross-reference the addresses between each system.

Search for the aforementioned MSG instructions, and in the tags list, filter out any produced/consumed tags.

ivannn · Jul 31, 2014

can you explain what filtering out produced/consumed tags does please?

Dravik · Jul 31, 2014

Lets you see if there are any on a given system.

You can then check the the tag to see what PLC(s) it is talking too.

How to verify PLC networks.

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