Architecture for discrete data collection

I was reading through the forum looking at possible ways to get discrete data out of a DH+ network of around 15-20 SLCs and PLCs, but couldn't really find a good answer.

1) One approach seems to be to use a ControlLogix to gather all the data through Message instructions. But if I have to track events in the range of 3000-4000, this doesn't look as a good solution to track discrete events.
2) What's your opinion on setting up an OPC server (Kepware?) to get data out of these PLCs directly instead of using a CLX concentrator?

The most straightforward method would be to use a 1784-PKTX card to connect your data collection PC directly to the DH+ network and use RSLinx as your OPC server. RSLinx would periodically poll each controller you need data from and serve that data to your PC application.

If your discrete data points are all grouped into arrays of data Words in the controller data tables, then 4000 points distills down to 250 Words, which divided up among 15 controllers would be about 16 Words per controller. Now it doesn't sound so bad !

You could collect all of that from one RSLinx station on the DH+ if you don't need data very quickly, or you might consider segmenting the DH+ network up with DHRIO modules and ENET modules in a ControlLogix 1756 rack so that each DH+ contains fewer nodes.

If you need "as fast as possible" updates of your PC applications when events occur in the controllers, then we are looking at an "Unsolicited Topic" in RSLinx and MSG instructions in each controller.

Tell us more !

Ken Roach said:

The most straightforward method would be to use a 1784-PKTX card to connect your data collection PC directly to the DH+ network and use RSLinx as your OPC server. RSLinx would periodically poll each controller you need data from and serve that data to your PC application.

Click to expand...

This is what I thought the best solution would be.

If your discrete data points are all grouped into arrays of data Words in the controller data tables, then 4000 points distills down to 250 Words, which divided up among 15 controllers would be about 16 Words per controller. Now it doesn't sound so bad !

Click to expand...

Yes the events are in Words and the events are not in the milli second range. Polling the data points every few seconds (4-5) would be fine. I just happened to come aross a system that was using around 200 Message instructions to poll the SLCs and PLCs. And the ControlLogix PLC was just used to collect this data. I just wondered if it would have been more economical and efficient to just use an OPC server to poll the PLCs.

Thanks!