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Default Execution Rate 15Hz of Communication Send Loop

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Hi NIVS experts!

 

From the link understand VS engine, the default execution rate of communication loop is set to 15 Hz.  I didn't find out how to change this default value in VS.  Since this Communication Send Loop transmits the channel values to the VeriStand Gateway, from which the Workspace gets the channel tables.  The data flow I understood look likes this:

 

                                                                 Data Channels                                             Data Channels

Communication Send Loop (15Hz)  --------------------->   VeriStand GateWay   -------------------------->  Workspace  (Data Logging Control (100Hz))

 

My question is: if the execution rate of communication loop is only 15Hz, does it make sense for the data logging control on the workspace to log data at a much high rate (say 100Hz target rate)?   Or how can I change the default execution rate of commnunication loop?

 

Thanks,

 

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Hi,

 

I guess you could find some information on this thread: http://forums.ni.com/t5/NI-VeriStand/Gateway-channel-caching/m-p/2602087#M3250

 

If I'm right, I'm quite sure this rate is not related to the data streaming used for data loggin or trend display.

 

Regards,

 

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Hi thumble,

 

Thanks for the thread, from which I learned how to change the default execution rate via labview API.   After I looked into the system definition file, I think maybe it is more straightforward to edit the .nivssdf file, which is essensially an XML file, by text editors.  There is an element: 

 

<Property Name = "Data Rate">

        <Double>15</Double>

</Property>

 

I assume changing the value from 15 to others will do the job.  That's only my guessing right now, I will do some experiments later. 

 

The point of my question is:  if the Data Logging Control  tool on the Workspace does read data from the Gateway, and the logging rate is higher than the default 15Hz, it will get repeated data (as you confirmed in your thread by scanning every 15ms (~67Hz)).  It's a little bit confusing if the end-user doesn't aware she/he gets the data throught the Gateway.

 

Thanks again!

 

 

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Accepted by topic author xhuang2

Re,

 

We have used both the "recording" and "streaming" API from VeriStand, and I can confirm that the data rate is equal to the one of the real-time data loop. The 15 Kz data source is used for providing quite slow data to the "read channel" API.

 

I guess that the Data Logging Control  uses the "recording" API, so it's not subject to the 15 Hz caching.

 

++

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Hi thumble,

 

Could you please be more specific on the "recording" and "streaming" API, i.e. what are methods you are using in the .NET framework? Or just show me a few lines of codes to call those methods?   I am new to NIVS, just got lost in the large Help files.

 

Thanks

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Re,

 

If you plan to use .NET you should look at the IWorkspace2 from NationalInstruments.VeriStand.ClientAPI assembly. If you use LabVIEW there is dedicated VeriStand palette. I think you can find samples in the API reference (part of the VeriStand help) or on the National Instruments web site.

Regards.

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Thanks.  It is crystal clear now 🙂

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