Using the cDAQ NI 9264 as a Function Generator

[OneOfTheWeirdFishes]

So I aim to output sine waves as high as 50kHz on the channels of the NI 9264. I have a sampling frequency of 400kHz using the Onboard Memory and the allow regeneration properties. I am using the Chassis NI 9189. It has a maximum update frequency of 1.6MHz according to the specifications (screenshot attached). However, when I try to go higher than 400kHz, there just is no output. 

However, when I try to output a sinewave of relatively high frequency, it becomes distorted. This is at around 10kHz - 50kHz. Unperiodic waves are produced. The 400kHz.jpg attached shows this. The  My initial though is that the samples were incorrect, however, on closer inspection this was not true and the samples should produce cleaner waves. The SineWave generator writes the samples to a text file so you will need to change that if you run the TestAOSineWave program.

All the other jpgs are of different sampling frequencies with the output frequency being = 3*SampleFrequency/40. These produce waveforms that are not as horrible as the one at the 400kHz. 

Does anyone know why this might be? How can I get cleaner waves at these frequencies? Is the hardware just unable to do this 400kHz sampling frequency?

Any reply would be really useful.

[WaiLee]

Hi, OneOfTheWeirdFishes

By referring to the 1st page of NI 9264 module Datasheet:
http://www.ni.com/pdf/manuals/374404a_02.pdf
It stated NI 9264 is capable to have a maximum sampling frequency of 25k per sample per channel/s only.
Therefore, by following the Aliasing rule, 25k/2 = 12.5k Hz (any output frequency below 12.5K Hz will not alias) but in order to get a complete clear signal shape, it's recommended to divide by 10 which is 2.5k Hz.
In short, it able to generate output signal which is less than or equal to 12.5k Hz only.

For More information about Aliasing calculation, kindly refer to this link:
https://zone.ni.com/reference/en-XX/help/371361R-01/lvanlsconcepts/aliasing/

Hope it help 

[OneOfTheWeirdFishes]

Hi WaiLee,

Thanks for the help. However, from my understanding, the 25kSamp/s rate is for when the task is using Non-regeneration. When a task is using Onboard regeneration, the sampling frequency is determined by the Chassis. This rate is 1.6MSamp/s as shown in the screen shot of the NI-9189 datasheet(AO Info.png, page 2 of the datasheet) : https://www.ni.com/pdf/manuals/376607a.pdf 

My question is why can't I reach this frequency when I am using onboard regeneration.

OneOfTheWeirdFishes