PXI 5124 positive polarity video trig

[serialdaq]

Hi

I'm working on measuring a differntial video signal.  I use PXI5124.I measure them individually the High component as one measurement and negative component as another measurement.Probe ground is connected to PCB ground.

I set the trig as TV-> NTSC-> Field 1-> DC coupling->ref Pos %10. polarity is set to negative by default.Everything is ok with the negative sync component of the diffenetial signal High level component. I get the correct triggered signal an get the snapshot of the signal.But when I try to  set the trig for positive sync I get a run time error.when I try to set the same trig settings an negative polarity, I always get the sync trig at different places of the snapshot. Triggering at the same place of window is important for me because I ask the operator to compare the measured waveform to a given before waveform.So st be sure that the trig will happen at the same delay time on all measurements for all samples of my UUT.

As a result is positive polarity video trig possible in PXI 5124 or How can I set the TV trig for a signal with positive sync for stable triggering.

Waiting for your immediate reply.

Regards

[Sev_K]

Hi,

As mentioned here the NI 5122/5124 supports negative trigger polarity in video mode, which means that the synchronization pulses must go to a negative voltage with respect to the back porch level. You can try to just measure the analog voltage and implement an Analog Edge Ref Trigger with either a positive or negative polarity. (see niScope EX Simulated Acquisition.vi in the example finder)