How can I get exact samp. rate 51200Hz instead of 51282.05 Hz?

[dfousek]

Hi !

I need to perform AI acquisition for 8 channels at 51.2kHz precisely.
I use either the PCI-MIO-16E-1 or the PCI-6071E boards.

Under TDAQ 7.4.1 I am able to achieve this, by setting a specific scan timebase and interval values at the DAQ_Rate().
In fact the "key" is to define a 4μs safety delay (instead of 10μs) in the interchannel scan sequence.

Shifting my code to DAQmx, I get from DAQmxGetSampClkRate() an actual samp. rate of 51282.051282 Hz.
Also, I get from DAQmxGetAIConvRate() an actual conversion rate of 416666.66667 Hz.

What should I do in DAQmx to achieve this precise rate ?

Dimitri

[Laura F.]

Hello Dimitri,

It is a hardware limitation that you cannot achieve that exact sample clock rate.  To produce the sample clock, the driver takes the onboard timebase and divides it by an integer to get the closest sample clock rate to what you have asked for.  The convert clock is also derived this way.  Many boards have a 20MHz clock rate so the closest you can get to the actual rate you want is 51.282 KHz or 51.150 KHz. 

Another option you might consider is providing an external sample clock for your DAQ device to use. 

Regards,

Laura