Sampling frequency

[MartinBioeng]

I am using Labview, simulating a signal through an external system (ie resistor) and recording the subsequent voltage. To do this I am using "Simulate Signal" which is connected to a voltage out via "DAQ assistant" and the subsequent recording is through Voltage in via another "DAQ assistant". All signals travel via a BNC 2110 interconnector.
My problem is that I want to record signals for longer than 10 seconds. For current recordings I have set the "Timing" to 1000 Hz and "Number of Samples" to 10000 (from the Simulate Signal). The "Clock Settings" for the voltage in and voltage out "DAQ assistant" are also set at 10000 samples to "read and write" and 1000 Hz. This works fine but if I attempt to change the Number of Samples to 100000 (to increase the sampling duration) an error comes up as follows: Error - 200284 occurred at DAQmx Read (Analog ID wfm NChan NSamp).vi. Under "Possible Reasons" it suggests that some or all of the samples requested have not been acquired. Its suggests increasing the sample rate. No trigger is used in the analysis.
Basically, all I want to do is record signals at a high sampling rate over a few minutes. If anyone can shine any light on this problem it would be appreciated.

thanks,

Martin

[Conseils]

Although not familiar with the exact software, I suspect that you are chaging the sampling rate or the buffer size (or both). Basically I suspect that you have a memeory overflow.

What you need to do is copy the aquired data and handle it yourself.

[Tristan_J]

Hi Martin,

The problem that you are seeing is due to a timeout occurring on your read, the solution depends on how you want your application to function:

1. Simply wire a value into the timeout input on the DAQ assistant equivalent to the length of your acquisition. - However this will cause your application to "hang" while reading the data.
2. A better solution will be to implement continuous acquisition (configuration option in the DAQ assistant), this allows you to perform multiple reads of blocks of samples continuously, inside a while loop or for loop (Finite number of reads).

Hope this helps

Kind Regards

Tristan
Applications Engineer
National Instruments UK & Ireland