The main purpose of the analog inputs on the 7344 is their usage as a feedback channel. As you correctly stated in this mode the acquisition intervals can be as short as the PID loop interval (62,5µs for 1 axis, 250 µs for 4 axes).
In this mode the analog input signals are used by the DSP on the board. You still can access the analog inputs with the read position function but these read operations are softwared timed and thus non deterministic.
If you don't use the AIs as feedback channels then you can read their values using the Read ADC function. The behavior is very similar as I described before. The readings are software timed and thus the timing is non deterministic.
Additionally the 12 bit ADCs of the 7344 can't be calibrated so the accuracy is very limite
d.
For accurate and equally timed AI operations I don't recommend the ADCs of the 7344. Better use an additional DAQ device for your measurements. If you use an NI E-Series board synchronization with your motion control application will be very easy thanks to the RTSI synchronization bus.
For more information please follow this link:
http://www.ni.com/dataacquisition/
Best regards,
Jochen Klier
National Instruments Germany
