cdaq AI and DI

[philwak]

We have a need to simultaneously sample AI and DI on a CDAQ chassis and would like to better understand the dependencies and limitiations that exist. AI is 9215 Di is 9421. We are sampling at 5000 samples /sec due to a limitiation on minimum sampling rate for the bridge input card that we have in the same chassis. I understand that it is not possible to have fully synchronised AI and DI samples, if not what is the limitation/error?

[Wayne.C]

Suggest you read the PFI section of the cDAQ manual for all your options.

[Raajit_Lall]

To add to centerbolt's suggestion, you can just specify the source of your di/SampleClock to be one of the internal clocks.  You can use the following signals as the source :

• AI Sample Clock
• AI Convert Clock
• AO Sample Clock
• Counter n Internal Output
• Frequency Output
• DI Change Detection Output

So in your application, you can specify the AI sample clock as the source for the di/SampleClock and this way you will just be using an internal source (AI Sample Clock) for the Digital Input sampling as well.

Again, as far as the specifications and limitations on the PFI lines or the AI sample clock, please refer to the NI cDAQ-9172 User Guide and Specifications.

Regards,