We are in the design of experiment phase and don't quite understand the synchronization of the PXI-4461 DSA. We need to measure very small relative phase differences over frequency, i.e. 0.03 degrees.
We have a single PXI-4461 channel that acquires a sine tone reference signal. That reference signal is also captured by our digital device under test. We use a FlexRIO and adapter board to capture the digital data.
A PXIe-6672 timing module serves the same clock to both the PXI-4461 and the FlexRIO. So the sampling basis clock is the exact same for both devices.
We program the PXI-4461 to 'Start' a finite capture on a digital edge created by the FlexRIO. That digital edge will also be synchronous with the master clock and announces the start of the digital capture.
One last note- the clocks can never be turned off, but the 'Start' could occur at any time synchronous with the master clock.
What could we expect for a time delay from the 'Start' signal to the first PXI-4461 sample? Would this delay be variable or fixed? In other words, would a phase difference between the digital waveform and the PXI-4461 capture waveform be fixed or variable from one run to the next? The absolute value of the delay can be dealt with. However, that delay has to be very stable- on the order of +/-50nS.
