How do I acquire data from a single DAQ channel for a specified length of time?

[Stewart]

How do I collect data from a single DAQ channel for a specified length of time (approx. 20 seconds) and plot this data versus the time required to obtain it? I would also like for the graph to update as the data is acquired if that is possible. Thanks.

[timy]

The easiest way is that specify the number of data. because, you may specify the sampling rate.
The best way is that synchronize with counter.
Good luck~

[Filipe A.]

Stewart;

The best way for you to achieve that would be by modifing the Continuous Acquisition and Chart(buffered).vi (shipped with Labview) to stop the while loop after the number of points which will represent the 20 seconds of acquisition is reached. As you know the sample rate, and the time you need the acquisition to run, you can figure out the number of point to be acquired by multipling the sample rate by the 20 seconds.
Hope this helps.
Filipe Altoe
Applications Engineer
National Instruments

[Stagnok]

Just for some clarification. If you sample rate is 1000 samples a second and you specify a buffer of 5000. You would have 5 seconds of data. You could manipulate these numbers to acquire the correct amount of data. However you would still need to write code around this in order to be able to reacquire whenever you want to.

[Ram2003]

Simplest way to update data will be to use a waveform chart and update chart single point at a time. You may use finite buffered acquisition (specify sample rate and number of samples) and update chart may be once in 500 ms.