Synchronized start of 3 measurement cards more accurate than approx. 40µs

[PhilippR]

Hello,

I programmed a 12 channel oscilloscope employing three advantech measurement cards. The three cards are supposed to start their data acquisition at the same time. I use a sequence structure that only contains the three VIs that each start the data acquisition of one of the three cards. A delay in the output arrays is the consequence. I measured the delay and changed the array-indices of the two delayed cards such that the delay vanishes on the output screen. The problem is, that the delay changes slightly with every new start of the VI. It varies around +/- 40 µs.

Is there any way to achieve a more accurate synchronisation given that the cards don't have a trigger output for synchronisation?

Thank you very much in advance for helpful comments.

[Jochen]

As Windows behaves non-deterministically you will always see a non-deterministic delay (jitter) in your application. The only way to eliminate this jitter is hardware synchronization. In fact for high accuracy a trigger signal is not enough but you will need at least a board clock synchronization, too, to avoid drifting during the measurement.

By the way: Almost all NI digitizers and multifunction boards provide hardware synchronization, starting from simple RTSI-bus synchronization (accuracy: several nanoseconds) and ending with high end T-Clock technology (accuracy: several picoseconds).

Best regards,

Jochen Klier
National Instruments Germany