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Sample Rate Differences in Data - cDAQ9178

Hello everyone,

 

I am currently having a small issue with our CDAQ9178 chassis using a NI 9234 Module to measure acceleration data using Signal Express.

 

We set the signal express to capture continuously at a desired rate. 

 

When we sample at a Rate of 2048Hz, we look at the data, and we have 2048 samples in 1 second, which is to be expected. 

 

We then set the Rate to 1024 Hz, we look at the data, and we have 1024 samples in 0.24 seconds, not in the 1 second that we had thought for a sample rate of 1024 Hz.

 

We then set the Rate to 4096 Hz, we look at the data, and we have 4096 samples in 0.96 seconds, not in the 1 second that we had thought for a sample rate of 4096 Hz.

 

I have attached a photo of the snippets from the excel sheet with another brief explanation and the project file we were using for signal express. 

 

Does anyone know what the cause of this issue could be? Are we misunderstanding the Rate option for DAQ or the Samples to Read option in Signal express?

 

We would just like to have data that matches our sample rate. 

 

We have changed about every setting in Signal Express that we could find, and have had no luck fixing this issue. My manager also tried this on a DAQ 4032 and he did not have this issue, so we believe it is something with the DAQ (cDAQ9178) itself.

 

Any possible leads or explanations to help resolve this issue would be greatly appreciated!

DAQ_Frequency_Difference.PNG

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From the specs of NI 9234:

Antoniooh_0-1687785368310.png

 

 

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or in short: Your DAQ can only run with certain samplerates, if you configure (better request) another samplerate, the driver will usually choose the next higher one and give no error. it's good practise to read the  actual samplerate property after configuration 😉

Greetings from Germany
Henrik

LV since v3.1

“ground” is a convenient fantasy

'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'


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