LabVIEW DSC 2011 / OPC Client IO Server / Can I write to the OPC Server using OPC Groups?

Question

Hi
I am using LabVIEW DSC module as a OPC client. My Shared Variables are binded to automation system OPC Server via "OPC Client IO Server".
On the OPC Server side it seems that the every write commands comes like one item at time, not like grouped.
Now I have tested this with the NI OPC Server as server and KepServer and LabVIEW DSC IO Server as OPC Clients.
When I use the NI OPC Server : OPC Diagnostics there are different events messages when the update request comes from KepServer or LabVIEW DSC.
There are log files on attachements for both write events.
Attachments:
Data from the KepServer.txt ‏6 KB
Data from the LabVIEW DSC OPC Client.txt ‏18 KB

Answer 1

Hello Pentsi,
I have received confirmation (from the PSE in the US) that DSC doesn't support group writes
There however work-arounds that might provide a solution:
- The first solution I had in mind was like this. Update the 50 OPC items as fast as possible.
Then use a 51st item as synchronization OPC item to check/indicate if new data has arrived/has been set/is available.
So LabVIEW sets 50 OPC values as fast as possible. The 51st value becomes goes from false to true when the first 50 values are written.
When this (51st) value is true on the OPC server you can read out the first 50 values (from the non-LabVIEW side). When you've read out these values, then you can set the 51st value back to false (from the non-LabVIEW side).
In the meanwhile at the LabVIEW side you wait until the 51st value goes back from true to false.
When it becomes false, then you write again those 50 values and afterwards set the 51st synchronization value from false to true.
And this keeps on going...
Note: Keep in mind that you only have to monitor one event at the side of the Automation System OPC Server in this case (the 51st) and based on an event occuring over there you can just do a group read of the 50 others. Also keep in mind that the maximum rate (6500 updates per second) from inside LabVIEW with the DSC Module OPC client I/O server was also mentioned in this document (http://digital.ni.com/public.nsf/allkb/63C043359F1​E12538625726E005BCD0C?OpenDocument).
Could this be a possible solution for your problem?
If you're using one of the OPC servers in this list (http://zone.ni.com/devzone/cda/tut/p/id/6417#toc19), then you can also use NI OPC Servers to update tags instead, which supports a faster update rate.
Kind Regards,
Thierry C - Applications Engineering Specialist Northern European Region - National Instruments
CLD, CTA
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