Is there a lower limit to sampling rate in DAQ card USB 6251

[Monica_Agarwal]

I am using a triangular ramp with 2049 points in each ramp. When I am sampling from 101S/sec to 100KS/sec the DAQ follows the triangular ramp, But as soon as I move to 100S/sec or lower, the DAQ gives only downramps (like a inverted saw tooth) twice instead of upramp followed by downramp in an ideal case. Is there a lower limit to sampling rates??

[Brad_K]

Hi,

By default, M Series AO uses a 20 MHz timebase with a 32 bit counter to generate the sample clock. 20e6 ticks/sec / (2^32 - 1) ticks = about 0.0047 Hz. There are ways to get even lower rates, but that's not your problem. The behavior you described makes me think this might be due to the combination of AO regeneration and USB buffering. What does your code look like?

Brad

[mikeporter]

The only lower limit to sampling rate are those imposed by Mr. Nyquist. What is the repetition rate of the ramp signal?

Mike...

[Monica_Agarwal]

hi here is how the code looks like. ALso attached are the ramp signals at 200Samples/sec and 100Samples/sec

[Monica_Agarwal]

The repitition speed of ramp is 24.4Hzwhen operated at 50K samples/sec for 2049 samples. The ramp is a continous signal