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PXI-5402 trigger signal disappears with too high offset


I have a PXI-5402 function generator with which I want to generate a sine wave with a small amplitude and comparatively large offset (think 50mV amplitude and 1V offset). An oschilloscope should measure the resulting signal through a device. 


Because the current is usually very low, I solve this averaging multiple measurements. This requires the measurements to be syncronized (i.e. always start at the same phase). I do this by sending the Sync Out signal (since this signal is synced to the sine wave) to RTSI0 as follows:

Fgen sync.png


However, it seems that when the offset is bigger than some percentage of the amplitude, the trigger completely disappears! I've measured the Sync OUT signal with the oscilloscope: at amplitude 100mV and 100mV offset, there is a trigger signal present, increasing the offset to 500mV and the trigger signal disappears.


To test this problem I'm generating a signal using the LabVIEW example: "Fgen Function Generator Trigger" without modifications. I then connect the Sync out/PFI0 connection of the fgen directly to the oscilloscope (monitored with InstrumentStudio) and I can see the trigger signal disappear live when I adjust the offset and the signal is not triggered anymore.


My question is, why does the trigger signal of a PXI-5402 function generator disappear at high offset?


A work-around that I found is the use a start trigger. But with the stanard function mode of the fgen, this trigger is generated only 1 time when you initiate the generation. So to average multiple measurements, I have to start and stop at each iteration, which is not ideal. If you have other suggestions for me, please let me know.

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