Synchronize DAQ Sample Clock to GPS 1PPS

[mdignan]

We've developed a data aquistion system that uses GPS to sychronize data with another romotely located  system.  Our system uses a PXI-6682 timing card, a PXI-4461, and several PXI-4498 cards.  The synchronization code is very similar to the example code on the NI website, http://zone.ni.com/devzone/cda/tut/p/id/6818.  We are setup to digitally trigger off the GPS 1PPS with a sample rate of 32kHz.   Because the DAQ sample clock is not sychronized with the 1PPS we are seeing one-half sample variablility in the data relative to the trigger.  We need better accuracy than one-half sample.  Is there any way to synchronize the sample clock to the GPS 1PPS and still be able to use GPS timestamps?

[ManLongAtNI]

Hello MDGN,

When you mention that you are setup to digitally trigger off the GPS PPS, is this responsible for both the Sync pulse and Start trigger for the DSA devices? If so, for the start trigger, since the 6682 has the ability to generate Future Time Events, are the PPS start triggers for the DSA devices defined at the same point in time?

Do the number of samples acquired vary for each PPS, within the same DSA device. As in, do we receive 32 samples between each PPS, or do we get 32 samples on one PPS, and then 33 on the next on the same device? Or do we get 32 samples on one 4498 in one chassis and get 33 samples on another 4498 in another chassis?