simulated device inputs

[acgrama]

Hello all,

I am reading samples (from C++, via the nidaqmx library) with values between 0 and 10000 from the input channel of a simulated device (NI-USB 9229) generating a sinusoid with min/max -60/60V!
Is this normal? Or have I just misunderstood something? (This page seems to imply that I should get values from the sinusoid)

Thanks a lot!
--Cristina.

Message Edited by acgrama on 03-29-2010 11:13 AM

[acgrama]

I am working in Differential mode, if that helps (it's the only mode available for NI USB 9229 if I understood correctly).

[John_P1]

Hi Cristina,

Which instance of DAQmx Read are you calling?

The DAQmxReadAnalogF64 (highlighted above) will scale the binary data into an actual voltage using the scaling coefficients from your device (set when the device is calibrated).  I suspect you might be reading back binary data which is the 16-bit code that the device is returning before scaling is applied.

Best Regards,

[acgrama]

Hi John,

thanks for the feedback, this seems like a valid explanation! Indeed, I am using the DAQmxReadAnalogF64.

Unfortunately, we have received the card from our clients, so I have no idea how it was calibrated.

Can I control this scaling step in another way? Or what can I do to obtain values within the expected range?

Thank you!

[John_P1]

Hi acgrama,

Another possibility is that you might be using a custom scale as part of your task.  Could you try the following:

1.  Acquire voltage using a Test Panel in Measurement and Automation Explorer. 

2.  Try running an Analog Input shipping example, such as ContAcq-IntClk.

If the above two tests show the same problem, could you try reading back the calibration coefficients from your device with the following function:

Best Regards,

[John_P1]

Oh I just noticed you are on a simulated device so calibration doesn't really apply to you.  Nonetheless could you try running the shipping example and test panel?

Best Regards,

[acgrama]

Thank you for the suggestion. I had forgotten about the shipping examples -- when it returned correct values, I realised I had forgotten a normalisation step in our app that modified the values: that was the culprit!

I'm sorry for having wasted your time! However, it was your suggestion that made me see the forest again instead of the trees, as it were 😄 (And I also learned about the calibration coefficients methods, which might prove useful to know in our project)

Message Edited by acgrama on 03-30-2010 04:04 PM

Message Edited by acgrama on 03-30-2010 04:05 PM