Using an external master timebase with NI9237 units in a cDAQ9188 chassis

[MalcolmS]

I have a cDAQ9188 chassis with 8 NI9237 modules that I wish to run at samples rates lower than the 1.613kS/s available from the internal clock on the NI9237. The "operating instructions and specifications" for the NI9237 mentions that the NI9237 can be configured to operate from an external master timebase and then refers to a link and reference for further documentation. Unfortunately the link "ni.com/info" and search string "cseriesdoc" mentioned don't work.

Ideally I'd like to run the NI9237 with an internal divisor of 1 and an external master timebase of 25,600Hz generated in the NI9188 to obtain a sample rate from the NI9237 of 100S/s. Presumably I can generate this external master timebase of 25,600 Hz from the cDAQ9188 "AI Sample Clock" by dividing the 80MHz Timebase by 3125 and routing it to the NI9237?

Without the documentation, or finding any related examples, it is difficult to see how using DAQmx from .NET and C# how I would:

(a) Set up the NI9188 to generate the 25,600Hz "AI Sample Clock"

(b) Set up the NI9237 modules to use this external "AI Sample Clock" rather than their internal clock and set their internal divider to 1.

If anyone has any pointers as to the DAQmx .NET interface properties and methods to use to achieve the above, or indeed comment on whether it is possible or not, I would be most grateful.

Best regards,  

[AudioVideoDisco]

Hi MalcolmS

Thanks for posting. I was able to access the General C series documentation page but upon futher investigation there does appear to be a broken link in there for the NI cDAQ-9188 User Manual.
Here's the full link for the documentation page: https://www.ni.com/docs/en-US/bundle/cdaq-9181-9184-9188-9191-features/resource/372780k.pdf

It is possible to obtain a sampling rate of 100S/s using the NI 9188 and the method you described, by using the sample clock of the NI cDAQ-9188.
The following link contains some examples using NI-DAQmx through text-based programming languages that you may find useful:
https://www.ni.com/en/support/documentation/supplemental/21/using-ni-daqmx-in-text-based-programming...

If you have Measurement studio installed on your computer you should also be able to find some relevant examples on your C drive in:
C:\Users\Public\Public Documents\National Instruments\NI-DAQ\Examples

I hope this helps,

Paul

Applications Engineer
National Instruments

[MalcolmS]

Paul,

Thanks for the links, examples and confirmation that the scheme I described will work. I'm in the middle of another project right now but will return to this problem next week and update the forum with the results.

Best regards,

Malcolm

[Duron-WTS]

Hi there,

I am having the same headache while running a NI9218 with a cDAQ-9174.

I wonder if you managed to solve the problem and in case you did if you could help me a bit.

I do not know how/where should I declare the use of the cDAQ clock instead the one of the 9218.

Thanks and regards,

Javier