OPC topic of rslinx controllogix

[wilsonzhu]

Hi all,

I have a question about OPC topic of Rockwell RSlinx, we use opc client in HMI to read the data in controllogix via Rslinx OPC topic. In the controllogix, we creat an array To_HMI[2000](real), and each tag to hmi(for example Pit_1103_hmi) we alias to To_HMI[index]element. In the HMI, OPC client will read individal tags in PLC such as Pit_1103_HMI, My question: does it increase the read speed for opc client to create To_HMI[2000] array? Thanks,

 

[Mark-]

Hello,

Most OPC clients do not normally issue reads, async or sync. They might to refresh the data but normally they setup a callback (OnChange) and wait for the server to notify the client that a tag has changed.

I guess you only want the values in the array and not other items of the OPC item. OPC has a lot of overhead to marshal the data back and forth.

IMHO it would be faster to execute one read of 2000 real values against 2000 reads of 1 real because of all the overhead. That applies to most protocols I have implemented.

Back to the first paragraph, if your client/server setup is not using callbacks, why not?

Good luck,

Mark
http://www.peakhmi.com/

 

[sthompson]

Hi all,

I have a question about OPC topic of Rockwell RSlinx, we use opc client in HMI to read the data in controllogix via Rslinx OPC topic. In the controllogix, we creat an array To_HMI[2000](real), and each tag to hmi(for example Pit_1103_hmi) we alias to To_HMI[index]element. In the HMI, OPC client will read individal tags in PLC such as Pit_1103_HMI, My question: does it increase the read speed for opc client to create To_HMI[2000] array? Thanks,

Allen Bradley says that the maximum packet size is 480 Bytes, or 120 DINTS. So, I would keep my Data Fetches that size or smaller. Knowledgebase article 60718.

Stu.....

 

[Steve Wiebe]

I'd second both of the above.
I'd do block reads of a reasonable size like so:
To_HMI[0],L50
To_HMI[50],L50
To_HMI[100],L50
and so on.
I'd probably use synchonous reads for this much data too.

Steve.

 

[wilsonzhu]

In My OPC client, I issue 2000 read of 1 read, but this 2000 data is in the same array in Controllogix, does it make difference if this 2000 data is not in the same array in PLC.

I'd second both of the above.
I'd do block reads of a reasonable size like so:
To_HMI[0],L50
To_HMI[50],L50
To_HMI[100],L50
and so on.
I'd probably use synchonous reads for this much data too.

Steve.