AI Sample Channel VI or AI Acquire Waveform VI

[labview1958]

I am a building a simple voltmeter.vi using NI-DAQ 6025E card and LV 6.0. I am a bit confused. Shall I use the AI Sample Channel VI or the AI Acquire Waveform VI? What's the difference? Both should give me a voltage reading.

[Dennis_Knutson]

Use whichever one you want. One returns a single sample and the other returns a waveform. Again, this sort of simple stuff can be found in the on-line help.

[Conseils]

It depends what you want to measure: -

If its a D.C. (unchanging) signal or very nearly D.C. then a single point measurement will suffice, its easy to implement saves bandwidth and processing.

If its A.C. and RMS measurement then you will need a cycle of data at whatever frequency the signal is at for a measurement, possibly more to allow for filtering and higher frequencys, more bandwidth required and higher programming overhead. The waveform aquire process samples continously for a set number of samples to ensure consitency of sampling interval.

[Dynamik]

Hi LabVIEW1958,

      Even if it's "DC" you're measuring, you may want to collect multiple points (a waveform) and calculate an average.  For instance, if you're collecting thermocouple data, the random per-measurement error might be a "large" precentage of the measurement (like several mV on a 50mV measurement).  Averaging, say 1000 points, @5KHz could help lots!

[FreshPresh]

Hi, I'm trying to run a Labview programme someone sent me but it is missing the AI Acquire Waveform VI. Could you send me the AI Acquire Waveform VI. Thanks

[GerdW]

Hi FreshPresh,

it doesn't make sense to ask in a 12 year old thread…

Those functions mentioned in these very old posts doesn't exist anymore. They were used in the "Traditional DAQ" driver, but now we use the DAQmx driver. See this appnote to learn about the functions to use…