zero values at start of buffer

[simply amazing]

Hi, I'm trying to read waveform data from a DAQ board using AI Read. My problem is that the initial values for each buffer always start from zero, regardless of the value at the end of the previous buffer. Why is this and how do I fix it? PCI-6035E and LabVIEW 6 if that matters.
-Paul

[SMeserve]

Paul,

I'm not sure that I understand your question.  What sort of behavior do you desire?  What do you mean by initial values?  With a little clarification, I think we can get this taken care of.

Thanks,

[simply amazing]

Ok, I'm reading in pressure and flow data from transducers and writing the waveform data to file. This data is recorded at 500 frames per second. Originally I had the buffer size set to 2000 samples, so every 4 seconds, the waveforms written to file would originate from zero. This is what I mean by initila values. The first sample data points in each set of 200 (ie- 1, 2001, 4001...) are zero, even though the transducers are not near that level.

[Sandra_T]

Hello Paul,

I see that you are using a PCI-6035E and programming in the LabVIEW 6 environment. I am assuming you are using the Traditional DAQ Legacy driver, since you are programming in LabVIEW 6. Is this correct? I understand you are trying to do an analog input task. Are  the pressure and flow data that you are collecting measured as voltages from your transducers?
What sort of acquisition are you making, continuous or finite? What did you set as your scan rate and scans to read?
Try adjusting the scans to read, does lowering this number make a difference?
What vis are you using to log the data?

The issue that you are seeing, is every 2000 samples measurement you are reading a zero as the first value.
Do you see these jumps on an chart indicator showing the data?
How have you programmed your applicaiton? Perhaps you can try running an shipping example that does a simple analog read to see if you see the same behaviour.

I am trying to understand your issue. Give my suggestions a try and please reply with some additional information.

Regards,
  Sandra T.

Applications Engineer | National Instruments