NI OPC Server Slow to update

[Tony_Dean]

Hi,

I am reading data from a compact DAQ 9184 chassis containing the following 3 modules: 9203, 9219 and 9213 via OPC but the fastest update rate I seem to be getting is about 0.7Hz even though the OPC client is requesting at a 2Hz rate. This only appears to happen with the compact DAQ OPC server (National Instruments.Variable Engine). I have several compact fieldpoint devices on the same network (using the National Instruments OPCFieldpoint server) and they update at the correct rate. I have set the 9213 module to high speed (rather than high precision) in case this was slowing things down but this has no effect. Is there a setting somewhere that I have missed?

[SarahLF]

Hi Tony_Dean, 

How many variables are you reading? If it is a large number, perhaps you could experiment with reducing data transport, like increasing the deadband for the updata or adjusting the requested rate for the OPC Client. 

Additionally, are you using LabVIEW?

If so then please see the following two articles which refer more to the shared variables themselves and how to troubleshoot them. 

Troubleshooting Network-Published Shared Variables

http://digital.ni.com/public.nsf/allkb/6E37AC5435E44F9F862570D2005FEF25

Why Is Accessing I/O Variables Through The Shared Variable Interface So Slow?

http://digital.ni.com/public.nsf/allkb/F18AEE4BE7C9496B86257614000C43DF

In particular ensure you are only opening and closing the references to the shared variables once if possible. Because of the polling nature of the server/client communication, it will be considerably slowed down if references are repeatedly opened/closed.

Regards, 

Sarah Flanagan

Applications Engineer

National Instruments UK and Ireland

[Tony_Dean]

Hi,

Thanks for the reply. I have approximately 60 channels in total. Unfortunately I am not using Labview, I am using a third party data logger which is connecting using OPC. It appears to be something to do with the OPC server (a National Instruments product) so I have no control over how it connects to the shared variables.

[SarahLF]

Hi Tony_Dean, 

It may be the number of channels that is causing the slow transfer speed. Is the first time you've experienced this issue? 

Can I ask, in what way does it appear obvious to be the Server? As in, are there other elements of the system that are possibly slowing the transfer rates also? For example, the 3rd party data logger? 

Unfortunately issues like this are relatively difficult to diagnose remotely. I would suggest mitigating any network communication from the network that isn't essential, to help reduce traffic.

Kind Regards, 

Sarah Flanagan

Applications Engineer

National Instruments 

[Tony_Dean]

Hi,

There are 28 channels in total on each remote network point, so 56 channels in total on the OPC server. It seems to be the server that is limiting the speed for the following reasons: Firstly, the OPC client (data logger) is connected to other OPC servers and is able to receive update much faster than the 0.7Hz rate that we experience with the 'National Instruments.Variable Engine' server. Secondly, If I connect to the server using another client instead of the data logger e.g. National Instruments OPC Explorer, this also updates at 0.7Hz irrespective of the update rate selected. Although there is other data on the same network, it is nowhere near its maximum bandwidth.