Fast Voltage Data Acquisition and Logging

[DePeppers]

I have been experimenting with Labview to create a VI that can record and log voltages for several analog in channels.  I am using a DAQ 9171 with a NI 9223 module to record with my VI at a sample rate of 500 samples a second.  My problem is I acquire the data at inconsistent intervals and not the intervals of my sample rate.  If anyone has some knowledge or an example, they can dole upon me it would be much appreciated.

[Jay14159265]

You don't need to do timing in your loop, your samples are already timed by the sample clock. 

[Jay14159265]

Try this and the dt is built into the reading: 

[DePeppers]

I can get the dt component of the waveform but I cannot get the right elapsed time in my .csv right.  It only writes a value of 1 for every time value in the column.

 

[DePeppers]

Here is the VI

[Jay14159265]

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@DePeppers wrote:

I can get the dt component of the waveform but I cannot get the right elapsed time in my .csv right.  It only writes a value of 1 for every time value in the column.

 

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dt is a fixed value (time between samples). You have the start time(t0), dt and n samples so to get your sample time you must do <t0> + <dt>*<n>

[mcduff]

There is a lot to be desired with that VI.

• You are downloading a single point at a time
• You have ever growing arrays
• You never stop or clear the task

Here is a quick rewrite, you could still improve it.

[mcduff · Accepted solution]

Should have tested first. See mod, need a sequence structure with dialog.

[DePeppers]

Thank you for the enlightening information.  I was hoping there was a simpler way to display elapsed time next to the recorded data to confirm the sample rate and dt.  As you explain it for my VI Jay, we need to take a component and compute parallel to the data acquisition.  And the sample rate is used to compute the dt and makes no errors, so it is perfectly fine to use it to calculate elapsed time and dt.

[Jay14159265]

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@DePeppers wrote:

 I was hoping there was a simpler way to display elapsed time next to the recorded data to confirm the sample rate and dt. 

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There is a simple way to do this, wire the waveform data type wire directly to a waveform chart and set to show elapsed time.