sample rate using USB6211

[BOX]

The programmer who working with me is making LabView software for my experiments.   I'm using USB6211 and Window XP with two CPUs.

I want to get 10K samples per second from three channels and display the signal in graph continuously while the measurements keep going.

It may be huge size of data but I'm doing it only for several seconds.    The progrmmer told me, however, that the data can not be show continuously. 

Instead, the data is shown after the measurement is done.  The whole data collected during certain period of time is shown at once.

That is not what I want.  I want to monitor the signal during the measurement.   But he said, the USB is slow and cannot work with Labview that fast.

If I lower down the sample rate such as 10, it may work, he said.     Is there a way that I can collect data with 10k and show them in graph continuously?

Thanks.

[Dennis_Knutson]

Depending on what your sample rate is, it should be pretty straight forward to acquire and display 10k samples. For example, if your sample rate is 10ks/s and you request 10k samples, you can update your graph every second. If your sample rate is 20ks/s and you request 10k samples, you can update your graph every 500msec. On the other hand, if your sample rate is 5ks/s and you request 10k samples, you will get an update every 2 seconds.

I'm not sure your programmer is very experienced with DAQ or LabVIEW or there is a lot of other information being left out. Other processing and file writes could slow things down but there are advanced techniques that can be used. Best place to start is with the shipping examples.

[BOX]

I can see how it works now.  Thanks.    The LabView reads the data using while loop.  The programmer said that the while loop can not update as much as sampling rate such as 10ks/s.    Is it true?  Then, how fast it can be update?  He said it is related to Window or USB things.  Then is it possible to read and show the graph in 50 ms at 10ks/s ?

Thanks in advance.

[Steve_B]

Hi BOX,

The DAQmx Read will return data into LabVIEW memory each time it is called. You will have to be sure that you call this function often enough in order to avoid overflowing the buffer that will hold the data. You can configure the DAQmx Read VI to return a large number of data points at each call so that you do not have to call the DAQmx Read at 10kHz, but at a fraction of that. The rate that the loop can iterate is system dependent and on a Windows OS can be on the order of several milliseconds. You can graph the data as it is returned by updating the graph indicator in the while loop. If you are set up to sample 1 channel at 10kS/s and you set your DAQmx Read VI to return 5000 samples, you only need your loop to update at 2Hz.