PCI-6070E sampling rate

[skim2]

Datasheet for PCI-6070E only specifies the max sampling rate.What is the resolution for sampling rate? For example, I am trying to set the sampling rate to 750Hz, but I believe it returns the actual sampling rate different from 750Hz. Are there some discrete frequencies that the card accepts for samling rate?

Thx

[Mcdan]

Skim2,

Your E-Series device divides down a 20 MHz clock to produce the sample clock.  The driver should pick the first integer divisor of the 20 MHz clock which results in a clock rate greater than or equal to the sample rate you specify.  In this case, I would expect that the drive would pick a divisor of 26666, which would produce a sample rate of 750.01875... Hz.  You can read back the rate the driver chooses by reading the DAQmx Timing Property Node -> Sample Clock -> Rate.

I hope this helps,

Dan

[skim2]

Thanks Dan for your rapid response. Now I have a good understanding of how the sample rate is generated.

Question -  2^14=16384 & 2^15=32768. How did you come up with the divisor, 26666?

Sang

[Mcdan]

Sang,

The divisor does not need to be a power of two.  It can be any integer from 2 (though this is invalid for rates that the 6070 can support) to 2^24.  This gives a possible sample rates from 10 MHz to 1.19 Hz at any integer divisor between these two numbers.  For acquisitions slower than 1.19 Hz, the device can also devide down a 100 kHz clock to produce a sample clock.  Again, the divisor is any integer between 2 and 2^24.

So for 750 Hz, I divided 20,000,000 by 750.  This gave me 26666.66666.  Since the driver will always pick a divisor which gives you a sample rate greater than or equal to the rate desired, it will choose 26666 rather than rounding to 26667.

I hope this explains things,

Dan

[skim2]

Cool! Thanks Dan.

Sang