DAQ Assist Continuos High Speed Display

[Cholst]

I am using the DAQ Assist to read in voltage data and display it as a scrolling chart. When I set it to take "N Samples" it works well, but wont display that data until the N samples have been collected. When I switch it to a continuos mode and set it to take 1 sample buffer at the same rate (20kHz) it actually samples much slower. Any suggestions about how to get a continuous chart that still shows the the data at full speed?

Thanks

[caunchman]

Well a couple of things

   What DAQ are you using, is it a USB interface, and are you using a USB 2.0 or 1.1, can run out of bandwith fast with 1.1, also what else do you have going on in the background can your computer handle the 20Khz?

    Also using the DAQ assistant is the best thing to sue when reading continous samples.  Some times its better just to set up a task to perform this operation.

    How many samples are you actually reading? When I record at 6000 Hz I ussually only read 1000 samples and write 6000 to file.

Hope this helps.

Chris

[Cholst]

Im using the USB-6210. I know that the computer can handle the data because if I tell it to take N samples then it does, but it wont display them on a chart until all of the samples are collected. If for example I tell it to take samples 15k samples at 15kHz then it outputs data to the chart every second, and has a gap of about 1/20 of a second.

What I am looking for is getting the same output graph when I ask it for 150k samples at 15k (updating every 10 seconds) as when I ask it to run continuously at 15kHz and see the graph scroll at real time.

thanks,

[RavensFan]

The DAQ assistant, while it is great for getting a quick and dirty DAQ task up and running, isn't really designed for high speed data acquisition with precise control.  You will likely need to use the lower level DAQmx functions.  Start a task, acquire chunks of data in a loop, end the task.  You may need to pass the data off to a parallel loop for data processing, display, or logging using a producer/consumer design architecture.  Take a look at the DAQmx examples in the example finder.

If you right click on your DAQ assistant and select Open Front Panel, it will turn the Express VI into a subVI that you can open and see how the underlying DAQmx code works.

It may even be a matter of selecting continuous samples in your DAQ assistant, a small number of samples to read, have it in a loop that iterates enough times until you have collected your larger number of samples.

[caunchman]

There are also numerous exapmles of gathering that data you can get from just using the help section.  I'll try to upload a VI later on.