Not achieving maximum sampling rates with the cDAQ-9172

[Scotti]

Hello,

I'm attempting to sample analog signals with the NI-9221 and NI-9206 modules on the cDAQ-9172.   It appears that with either the NI-9221 or NI-9206 I should be able to sample continuously at 250kSamples/Sec for the 9206 and at 800kSamples/Sec for the 9221.  Unfortunately when I attempt to sample at rates faster than 100kHz, I get this error message:

Error -200279 occurred at DAQ Assistant

Possible Reason(s):

Measurements: Specified sample rate is higher than the fastest rate supported by the device.

Property: SampClk.Rate
Requested Value: 150.0e3
Corresponding Value: 150.375940e3

Maximum Value: 100.0e3

Device: cDAQ1

I'm assuming this is because my sample clock is being generated from the 100kHz Timebase signal?   And this is so, how do I change my system to run off the 20MHz Timebase?  I'm using SignalExpress to perform my data logging, I'm not using a Labview script or anything like that.  I don't have a lot of experience with NI software or DAQ equipment, so forgive me if this is a naive question.

Thanks for the help in advance.

[pflores]

Hello Scotti,

The aggregate sample rate is listed at 250 kS/s. this means that you must chare these samples across all input channels. (ex: If you are reading 2 AI channels, they are limited to 125 kS/s each). For the case you listed above, this would only be an outcome of the 9221 device (as you cannot divide 250 kS/s by an integer to get 100) if you have 8 analog input channels. If you are only using one channel per device, then this would not explain this behavior.

Do you think this is your issue? If not, then post some more details on how your code looks. If you use Test Panels in MAX, do you see the same behavior?

Regards,