Missing CompactDAQ data

[Cabman]

I'm using the 9205 Analog Input module to capture a waveform on a CompactDAQ system. I'm simply creating a task then using the "Analog Wfm 1Chan NSamp" form of the "DAQmx Read" VI. No other tasks for the other modules are created, and I'm only using one channel on the module.

The problem is that after every 120 samples there is missing data. I have a 100 Hz sine wave connected to the input. Here is the data displayed as a waveform:

Also, the sample rate seems to be about 13000KS/s instead of the expected 200000KS/S. I've tried changing the sample rate and sample mode with the "DAQmx Timing.vi", but nothing changes. In the above example I specified 250 Samples per channel.

I'm using TestStand to call a create Task VI, then passing the task to the Read VI. I don't think that has anything to do with the problem but I thought I'd mention it.

Any ideas?

TestStand V3.1

LabVIEW V7.1

[Sandra_T]

Hello Cabman,

I see that you are using the NI 9205 to acquire an analog finite acquisition. I was unable to see the picture that you posted. Please re-post it as an attachement.

In your code:

1) Are you trying to do continuous acquisition or finite acquisition?
2) How are you programming you task? (screen shoot of your code would be useful). Do you have everything in a while loop or do you have only the read in while loop (this is what you want to have)?

I would start with one of our shipping example to test this issue. In LabVIEW, Help>>Find Example to open up NI Example Finder. In the browse tab, Hardware Input and Output>>DAQmx>>Analog Measurement>>Voltage. There are a bunch of examples here that you can take a look at. Make sure to check your device is listed in the Requirements window (lower right hand corner). This means your device is supported by the example. The ones that start with Cont usually means continuous acquisition.

Test these example to see if you are seeing the same behaviour with your code.

Regards,
  Sandra T.

Application Engineer | National Instruments

[Cabman]

Thanks Sandra,

Looking at the examples I realized I had my Timing VI before the Config Channel VI which is why it had no effect. Doh!

It working correctly now.

Dave