High-speed aquisition time stamp

Question

I am using traditional NI-DAQ with a 6071E board and acquiring data at very high rates using AquireWaveforms.VI I want to save this data in a text file with either a column of time first or even a column of time before each channel (anywhere from 1-64 channels). Because I am acquiring at such high rates, I suppose I want to be able to extract timing data from the Hardware since I'm not looping and any software timing wouldn't be accurate. Also, if at all possible I want to be able to have the time for each measurement from each channel so I can include the phase shift that comes with multiplexing. Is any of this possible? I really need resolution much better than 1 second. at least to the millisecond, but I am looking for even bette
r than this.
Thanks so much,
Rick

Answer 1

The waveform carries a DT (delta Time) component.
Use the GET WAVEFORM COMPONENTS function to extract the DT. That should be the actual dT used, not necessarily the rate you asked for.
If you have a DT number, you create the array with a FOR loop:
For I = 0 to NSamples-1
Time[i] = i * DT
As far as the inter-channel time, the minimum value is a property of the card, but it's also controlled by software: LV can extend it.
I don't know about the express VIs: I never use them. But the original AI CLOCK CONFIG, has an input where you can specify it.
If that doesn't work, and you have access to some test equipment, you can find it out for yourself:
Set up a ramp generator for 0.0 - 1.0 V at 1000 Hz.
This means the voltage is
changing 1 volt per mSec.
This means the voltage is changing 1 mV per uSec.
Wire the ramp generator to channels 0, and 10.
Perform a DAQ operation, with all channels 0-10 active.
Pick out a portion of the waveform, where the voltage is increasing on all channels (exclude the drop at cycle's end). Ignore channels 1-9.
Subtract the channel 10 array from the channel 0 array.
Average the result array and divide the average by 10.
The average value, in mV, is the channel delay time, in uSec.
By comparing channels 0 and 10, you're measuring 10 intervals, not one, so you're more accurate.
Steve Bird
Culverson Software - Elegant software that is a pleasure to use.
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