回复： How to read data from NI 9239 in lower sample frequency with cDAQ 9178 slot.

[rayyang]

Hi

The NI 9239 user guide said the lowest sample freq is ~1.6kHz.

And I need to log the data to PC's HD for more than 5hours.

When I start the .vi, buffer overflow error occurs.

Wondering  is there any method to reduce the sample freq or use some soft timer to trigger the 9239 in ~10Hz.

I only have the cDAQ slot, no cRIO slot.

Any suggestion would be helpfull.

Thank you.

[Cece-Zheng]

The main reason for this problem is that the sampling speed does not match the speed of data read. That is to say you do not read the data in time to cause a buffer overflow.You can set up the speed of data read in the program.

[Henrik_Volkers]

If you read at 1.6 kHz and only need data @ 10Hz   you can

-only record every 160 value and ignore the rest

-or take the mean of 160 values  ..   and store that value (in signal processing you find resample / decimation vis that do the job)

the PC will be bored anyway with such low samplerates 😄

[Cece-Zheng]

Is not your problem overflowing the cache? The reason why the cache will overflow is that you do not read the data in time, and the sampling rate is actually have no relationship.