What is the timing resolution in M series DAQ device specification?

[jay99]

HI, All~

please, Anyone who tell me about timing resolution~ I don`t understand means of 'timing resoution' in M series DAQ device specification.

At NI 625X specification sheet,

timing accuracy..................50 ppm of sample rate 

timing resolution.................50 ns

I'm waiting for your help~

thanks~

[MRothman]

Timing accuracy of 50 ppm means that the sample rate error can be up to (50/1,000,000)*DesiredSampleRate.

For example, if you choose a sample rate of 1khz, then the sample rate error is 50/1,000,000*1,000=0.05 Hz. Which means that the actual sample rate that will be used is (1,000 +/- 0.05) Hz.

- Mike

usb daq boards 

[John_P1]

Hi Jay,

To answer the other half of your question, timing resolution of 50 ns means that you can choose sample clock periods with a resolution of 50 ns.  For example, you may select a sample rate of 1 MHz (1000 ns sample period), but if you were to select a sample rate of 900 kHz (~1111 ns period), this would be coerced up to ~909.09 kHz (1100 ns period).

Another way to think of it is that the sample clock is a divide down from a 20 MHz timebase.  So, you can only choose rates that are integer divisors of 20 MHz.  For example, 20 MHz / 22 = ~909.09 kHz. Sample rates coerce up for input tasks in DAQmx and are rounded to the nearest value for output tasks. 

One of the improvements we have made on our new X series boards (e.g. 6351) is a timing resolution of 10 ns.  This means that the X series boards use a 100 MHz timebase.  The X series boards are priced comparably to the equivalent M series board, so if you are purchasing new hardware and PCIe or PXIe is an option, I recommend you take a look at our 635x.

-John

Message Edited by John P on 08-27-2009 10:29 AM