Thread Starter


I want to "see" data from an Allen Bradley RsLogix5550 processor over ethernet using a SIMPLE VB app. I have RSLinx Pro and VB6 Pro. I can paste OPC link from RSLinx into Excell and see data updating much faster than it was with DDE. How do I do the same with VB? Thanks.
Thanks for the info, especially the first article. I need OPC to work. I am monitoring fuel schedule on a gas fired turbine and I need to see data FAST. I was hoping to trend data for about 5 minutes on around 10 analogs and about 20
discretes. I need update to be at 50ms or less. I tried using RSLogix 5000 trends, but am limited to 8 items so I had to use three laptops and it seemed to bog my ethernet down. Thanks again.

Steve Myres, PE

If you have trouble sustaining that data rate, would it be practical to buffer the data in the PLC, until after the test? Or the data can start to be read during the sample interval, but will not necessarily have to be synchronous to the test, because of the buffer. Your application will need to buffer about 1 MB of data, and you can get plenty of memory for that in the ControlLogix, depending on the volume of your code and other data.
Sorry, been busy! How do you do this? This sounds like a good scenario to review data after the initial light off. Thanks, Brad.
We've switched from using RSLinx as an OPC server in our VB projects to an ActiveX control we found at "wwww.automatedsolutions.com":http://wwww.automatedsolutions.com . (Mainly because of performance issues using RSLinx) We've had some very encouranging results from this control where I'm sure you can get down to your required 50ms read cycle or better. It has the capability of reading Logix5000 User Define Types (UDTs) directly, which we've used extensively.

I would highly recommend buffering data (or UDTs) within the PLC. In practice we move new PLC data into a PLC UDT array ( the next available position) then flick a ToBeProcessed bit for that new data. (Each buffer UDT array element has a ToBeProcessed bit). The VB app would read the entire buffer array and check which entries have the ToBeProcessed bit on. The VB app would extract the new data and write back to the PLC 0s to the extracted ToBeProcessed bit entries. ( The PLC checks this bit before it overwrites with new data to ensure it was processed) This ensures your PLC will continue logging if you VB app is delayed or down.

Good Luck
Fil Rossi