Digital analog synchronisation

Question

Hi
We have a system using a PCI6052-E which is set up to read two analog channels
at a sample rate of 133kHz. We now need a digital input to be synchronized with
the analog channels so that we know on which analog sample a digital transition
occurred. Is this possible using the in built counters or is there a way to tie
the analog sample clock to a digital sample clock? Will either of these
options limit the maximum sampling rate we can run at?
Any suggestions greatly appreciated.
James

Answer 1

Brief outline of concept:
- Configure counter to use analog sample clock as its timebase source (the signal that causes count register to increment).
- Configure counter to use encoder pulse as its sampling clock (aka "Gate" for buffered measurement in traditional NI-DAQ).
- Start counter task before analog input task, so that counter sees every sample clock edge.
- A little processing.  Example: find out the encoder position (in # of pulses) at ai sample # 123456.  Use function with name something like "Threshold 1D Array" which has an output called "fractional index."  Feed in the array of buffered count values and the number 123456.  Round the fractional index down to the next lowest integer.  That rounded index value is the encoder pulse count you want.  Scale as needed.
There's also a way to capture a count with every ai sample, but it's going to give you ~1000 reps of each count value between increments.  Less processing though, and possible preferable if you need to do calcs on-the-fly.  Might require use of DAQmx and "duplicate count prevention" property.
-Kevin P.