Using IP Addresses to show order in a "daisy chain" on Citect

[cjthemack]

Hi Everyone

Im looking at networking a set of machines that can have their order
swapped or even totally removed.

They are all physically in a daisy chain.
Im looking at buying some AB ETAP devices which have set IP Addresses.

With this data I was hoping to somehow program with the Scada to be able
to not only read the PLC in each machine but be able to show what order they are in...

So I was hoping somehow i could setup Citect to be able to read the and use like a tracert command to show the order.

Or if anyone would have any other ideas???

 

[robertkjonesjr]

At layer 2, i.e. through Ethernet switches, it may be possible to get the order. You will need to take a statistical approach to this by measuring multiple <somethings>, like ping response, or ModbusTCP response time, or whatever, and then you might be able to tell which order they are in. If you can get the resolution you need out of the OS you are on (assuming Windows).

If you look up switch latency for a packet, I think you will find it is VERY fast, generally, especially on typical Industrial Control Networks that are over-provisioned and therefore lightly loaded.

Try here:

https://w3.siemens.com/mcms/industrial-communication/en/rugged-communication/Documents/AN8.pdf

You will be looking for timing differences on the order of microseconds. I have done this with ModbusTCP response times for a customer ex post facto (i.e. he gave me a packet trace) and could prove his drives were not hooked up in the order he thought they were. I could detect, with many transactions, the statistical shift in the mean response time for each switch hop on the order of microseconds.

By the way, with this latency, not sure it really matters much in the grand scheme exactly what order they are in as far as regular performance is concerned.

Not exactly sure how to do it with SCADA. Suggest doing it by hand a couple of times to see what it really takes and see if it is worth the effort. Switches that support LLDP would be preferable here - you just ask them with SNMP who it's neighbors are and it would tell you. No idea if your devices support this.