6608 Period or Frequency sample rate limit

[Swimmer]

I'm using a 6608 counter/timer card and want to measure the period of a variable frequency square wave signal.

I need the period of each rising edge as this same rising edge is used to externally clock my analog DAQ cards.

In this way I know the period of time between individual position measurements.

I used the example VI Meas Dig Frequency-Low Freq 1 ctr.vi and added the appropriate code to make it read continuously.

I'm using a function generator to test the hardware and it seems to work well up to 100KHz.  After that the 200141: Data was overwritten before it could be read - error occures.

This error occures at exactly the same number of pulses every time I try running at a given frequency.

I have been unable to find any information that would clue me in to a limit to the frequency of a period measurement on this card.

Has anybody else had a similar experience and is this a limitation or is there a setting I'm missing?

Thanks

[Aaron_W. · Accepted solution]

DVS,

Thank you for posting on the NI Forums. This buffer overflow error that you are seeing is because our counter/timer boards have a two-sample FIFO buffer for counter measurements. What you are running up against is the fact that you are taking measurements faster than your computer can DMA transfer these measurements off of the buffer. I would suggest trying to use the other counter measurements such as 'two counter - wide range' to see if this would help you take higher frequency readings. 

Our documentation on the FIFO is found here. I hope this clarifies the issue somewhat, thanks!