Labview LeCroy LT264 Lightning Impulse Test Signal Loss

I use Lecroy LT264 oscilloscope to trace lightning impulse test (1.2/50usec waveform). I have driver for labview and use edge triggered example. One impulse is not shown in every three impulse. What could be the reason ? Thanks for your interest.

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Also you can download code here : http://forums.ni.com/t5/Instrument-Control-GPIB-Serial/LeCroy-LT264-Lightning-Impulse-Test-Signal-Loss/td-p/2510994

Solution

Ok, I solve the problem. The reason is trigger level. I had set 40 V or 80 V. However when I set trigger level 150V, program shows all impulse.