Sample speed slower with a new DAQ

[Mrhighsky40]

Equipment:

    NI 9189 cDAQ directly connected by Ethernet cable

    NI 9209 Analog Input Module

    NI 9264 Analog Output Module

    Strain Gage

    USB X Series DAQ

Issue: 

    Previously my setup worked for collecting data at a frequency greater than what is needed, but this was using a USB X Series DAQ. I have moved the setup over to the system listed above and the frequency of data collection is around 2 Hz max, the values are as expected, but at a much lower resolution than I desire.

    The full program has 7 AI channels which should give ~60 S/s/channel and the AO seems to work fine. Also, when deleting all but one task and channel in the Labview file the frequency less than doubles (most likely due to a decrease in latency) so I don't think my Labview file is the problem.

    This leads me to believe it is some kind of user error, but I am not sure what I need to change in order to have the data collected properly and I haven't seen anyone else with a similar problem. Any advice would be greatly appreciated.

[Kevin_Price · Accepted solution]

The spec sheet for the 9209 shows 2 modes -- high resolution and high speed.

High resolution mode needs 52 msec per channel, high speed needs 2 msec per channel.

Apparently, high res mode must be default and your 7 channels will require 364 msec to convert.  So that'd max you out at under 3 Hz.

High speed mode would get you to 14 msec for 7 channels, which would slightly exceed your desired 60 Samples/sec/channel.

I haven't used the device, but I'd guess there's a DAQmx Timing property node you can configure to set high speed rather than high res mode.

-Kevin P

[Mrhighsky40]

Thank you so much Kevin! Changing it to high speed using the DAQmx channel property AI.ADCTimingMode tripled the frequency. So it was more than just that, but your solution helped me find this thread:

https://forums.ni.com/t5/LabVIEW/NI-9209-DAQmx-sampling-rate/td-p/3338730

That thread led me to the voltage - continuous input example in Labview.

From there I changed the code from collecting a single sample at a time and plotting it to plotting a group of samples at once and voila! It is running at a much more respectable frequency.