Write to Measurement file at different Sampling Rates

[GasperB]

Hello Experts,

I am new to LabView beyond the basic use. I am measuring data at two different sampling rates (1000 Hz and 200 000 Hz). I would like to write data to a measurment file (or files) and I need to make sure the data is synhronized. 

I have a cDAQ NI9185 with a NI 9203 (reading flowrate and temperature of a process continiously at 1000 Hz) and a NI 9222 reading from a fast pressure sensor at 200 000 Hz. How can I write this data and keep the times synhronized. example: Every 200 samples, one sample of the slower card is read, keeping everything in sync. 

Thank you!

[GerdW]

Hi Gasper,

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@GasperB wrote:

How can I write this data and keep the times synhronized. example: Every 200 samples, one sample of the slower card is read, keeping everything in sync. 

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Several suggestions:

• Don't use ExpressVIs, the will make your code more complicated in the end.
• Learn basic DAQmx functions, as explained here and in all those example VIs in the example finder!
• Read waveforms with DAQmxRead, so your measurement data automatically come with a timestamp (and dt).
• Save all the data to a TDMS file (maybe even to different channel groups), so you got them in a compact data format.
• As you write waveforms to the file you will ALWAYS have timestamps for each sample in post-processing!

How well do you need to "synchronize" your data?

[dsb@NI]

Because your 9185 automatically selects the chassis backplane clock as the master timebase, your code (just) needs to share a start trigger for synchronized measurements.
Try code like this (I modified a shipping DAQmx example):

And I will echo some of Gerd's suggestions (emphasis mine):

• Read waveforms with DAQmxRead, so your measurement data automatically come with a timestamp (and dt).
• Save all the data to a TDMS file (maybe even to different channel groups), so you got them in a compact data format.
• As you write waveforms to the file you will ALWAYS have timestamps for each sample in post-processing!