Question about RSLinx OPC server polled messages rate...

TConnolly

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Does anyone know how fast the RSLinx OPC server polled message rate can update 350 tags over Ethernet for high speed data logging?
 
Hmmm I just tried to read an array of 320 DINTs from a Compactlogix into Excel using RSLinx OPC and I get "#NAME?" even with the polling set for 2000msec.

I went to copy a new link with fewere elements and RSLinx crashed...
 
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Well, with a block size of 100 elements I can set the rate as low as I want, but I am not sure it's really getting it done that fast...Excel is probably not the right way to test this...

EDIT: Well the biggest block size I could get to work in Excel was 122, so I not have 4 OPC links to get 350 REALs from a CompactLogix.

I changed the polling rate to 20msec and added a rung to simply increment one of them every scan. To my naked eye, it looks like its doing it at least as fast as Windoze can repaint the screen...
 
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Hello,

Maybe I am not seeing the forest for the trees but why use polling? Why not use the deadband setting and exception reporting? I would assume the logging functions are separate from the data collection functions.

Of course, I could be totally wrong.

Regards,

Mark
http://peakhmi.com/
 
Well, with a block size of 100 elements I can set the rate as low as I want, but I am not sure it's really getting it done that fast...Excel is probably not the right way to test this...

EDIT: Well the biggest block size I could get to work in Excel was 122, so I not have 4 OPC links to get 350 REALs from a CompactLogix.

I changed the polling rate to 20msec and added a rung to simply increment one of them every scan. To my naked eye, it looks like its doing it at least as fast as Windoze can repaint the screen...

Paul:

I have run into this before when we were trying to extract Data from a ControlLogix. Allen Bradley says that the maximum packet size is 480 Bytes, or 120 DINTS. So, I am surprised you managed to squeeze in 122. Knowledgebase article 60718.

Stu.....
 
Yeah, I knew there was a packet size limit but I thought RSLinx would take care of that (break the blocks up for me). Not sure why it worked with 122 and failed with 123...If I left it long enough I may have seen errors with 122, but I only left it running for a minute or two while I played with the polling rate.
 
Yeah, I knew there was a packet size limit but I thought RSLinx would take care of that (break the blocks up for me). Not sure why it worked with 122 and failed with 123...If I left it long enough I may have seen errors with 122, but I only left it running for a minute or two while I played with the polling rate.

I also would have expected RSLinx to take care of splitting the Data up to proper sized Packets. Apparently AB didn't make it that smart. I would also have expected RSLinx to generate an error as soon as you tried to read anything more than 120 DINTS or REALS.

Stu.....
 
I also would have expected RSLinx to take care of splitting the Data up to proper sized Packets. Apparently AB didn't make it that smart. I would also have expected RSLinx to generate an error as soon as you tried to read anything more than 120 DINTS or REALS.

Stu.....

Hmmm... Today, it will do 121, but not 122.
Looking at OPC group Diagnostics I see nothing which tells me that it's using DDE, not OPC.

I have two columns in excel, one with a block size of 121 which shows up under RSLinx DDE Client diagnostics, and a 2nd column with 122 which doesn't show up in RSLinx at all, it just shows "#NAME?" in excel.

The active topic list shows the working one, and the optimized packets lists shows it with an item count of 1, and it's doing about 187 to 191 packets per second with the polling rate set to 5msec.

I am whistle-bit again, so I'll let you do the math to see how much data is really being moved there...:)

Paul

Reading an array of DINTs, by the way...

RSLinx_Speed_Test.jpg
 
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Does anyone know how fast the RSLinx OPC server polled message rate can update 350 tags over Ethernet for high speed data logging?
My tests ended up with a polling speed of slightly faster than 10msec. This was using a Compactlogix, reading an array of REALs (not DINTS as I said earlier...same number of bits though) into Excel. Since the max size I could read in each block was 121, I used three links to break the data into small enough pieces to keep Excel from erroring.

This was a lot faster than I expected it to work. In my Topic config, any Polled Message rate setting less than about 8 msec yielded the same results.

RSLinx_Speed_Test_001.jpg
 
FYI, 512 bytes is a standard connection and 4096 bytes is a large connection. The PLCs often have a buffer limit of 4096 bytes.
The OPC will also split packets into chunks, so using a bigger block of data doesn't necessarily mean you will read/write it in a single packet. The PLC drivers that the OPC software uses will ultimately determine how it gets broken into chunks.
 

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