DAQ dynamic data

[Xiao@Gemini]

Hello everyone, I'm acquiring voltage signal using NI 9239 with rate 100Hz, samples to read 500 and continuous samples mode. I probe the output dynamic data please see the picture attached, the dt is always 0.00062, 1613Hz, I would like to save the data at maybe 40Hz or 60Hz, is there any way that I can change this to a specific value. Thanks very much.

[Bob_Schor]

Sigh.  You are using the Dreaded DAQ Assistant and its evil Twin, the Dynamic Data Wire.  How you get a dt of 0.00062 I cannot (yet) figure out, but something certainly is wrong here.

I recommend you make a simple VI with (if you must) the DDA (Dreaded DAQ Assistant), take one sample (no loops) and save directly to an indicator.  Do not wire an input to the Rate, but set it in the DDA.  See if you get the correct dt value.  If yes, start expanding "what works", checking every step of the way.  If no, then something is wrong with your DAQ, with your LabVIEW installation, or your PC ...

Bob Schor

[RavensFan]

That is the minimum data rate for a 9239 module.  Read pages 5-6 of the datasheet.  http://www.ni.com/pdf/manuals/375939b_02.pdf

If you want a lower rate, you'll need to read at the higher rate and downsample it.