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Old April 24th, 2018, 09:54 PM   #1

santanacasas is offline
Join Date: Jul 2012
Location: REYNOSA
Posts: 3
PLC receiving data from external devices (AB PLCs)

Hello everyone!

This is my first post, I am currently working as a control engineer in an automotive plant (4 months ago) that has all the PLCs communicating to a SCADA system.

Well, what I want to ask is how do I know if some data in my data table address is being received from an external device.

For example, there is some data that the SCADA system sends to N241:0 to N241:10 but I know that because someone told me, but how would I have known otherwise? How to trace the device that is send me the data from my program?

Best Regards
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Old April 25th, 2018, 12:28 AM   #2

mdim is offline
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Join Date: Jan 2013
Location: Sofia
Posts: 219
Ask the same guy!

Other than this is first to know what exactly is the type of your SCADA and have the development software for it and also have the knowledge how to search the desired information in this software.
Other way is if someone had created a datamap or mapping table or something like this during making the SCADA, so there in a spreadsheet you would have all this data.
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Old April 30th, 2018, 07:14 PM   #3
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Ravioli is offline
Join Date: Dec 2015
Location: United States
Posts: 51
As far as best practice, If I'm doing a message write to a PLC, on the destination PLC I always make sure the Data file / tag descriptors make it obvious which device the data originated from.

"New Recipe<-SCADA"
"Start Transfer <-XFERSLC"
"Start Motor <-PV"

Likewise if I'm preparing values for a message read, on the source PLC I will have descriptors like

"Ready for Transfer ->XFERPLC"
"Motor Running ->PV"

As far as trying to figure it out, on DH+ you can use something like FrontLine NetDecoder and try to figure out the source node

On Ethernet you can use something like Wireshark.

You can also tell if a Find and Cross reference show no indication of the value being modified locally, but they change, then something is changing it (a remote PLC or SCADA, or HMI), but you can't tell what one without some hunting.
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