use timing source temrinal to trigger a timed-loop to control sampling rate of analog signal

[scoombes]

Hello?

I am having a problem with setting the sampling rate of an analog signal that is being streamed into a PCI-6220 DAQ card. i am using Labview 8.0.

I need to display the data in real time for segements of varying lengths. I am using the DAQmx read function within a timed loop (with the "use built in timing source"), allowing me to sample at 1000Hz which works flawlessly.  The problem is that I need to increase the sampling rate, and therefore configure the loop to use the "timing source terminal"?.

I figure there is a clock on my DAQ card, but I cannot seem to accurately find/access/configure this clock to send a pulse to the timed loop to control the sampling rate.

I think I am confused because it seems the sampling rate can be controlled at the level of the DAQ card, and also within Labview via the timed-loop? or maybe at both points?

Basically I want to be able to see the data (via a chart) as it is streaming in while also making sure that the data is accuratley sampled at a specified frequency (>1000Hz). The analogue waveform I see does not need to be sampled so accurately, but i need to know tha the data file I have saved after each segment is accurate in terms of the number of data points within the specified time period. I have been able to achieve this with the  "use built in timing source" but that restricts me to sampling rates of 1000Hz.

Not sure if this all makes sense, but any help would certainly be useful. I feel that it should be quite straight forward to achieve, I just dont have the brain power to figure it:) and caffiene has yet to act as a viable substitute.

thanks in advance!

cheers

steve

[gwd]

Since you are using a timed loop you are doing a software-timed acquisition and you are pretty much at the upper limit of the possible sampling rates. Even now you may have some random variation in the exact sampling time.

You should start with some of the examples that use the on-board buffer and hardware timing. A good place to start might be Acq&Graph Voltage-Int Clk-HW Trig Restarts.vi, or perhaps simpler Acq&Graph Voltage-Int Clk.vi.