Reconfigurable Oscilloscopes Shows Delayed Acquisition When Using Digital Trigger

Updated Feb 9, 2026

Reported In

Hardware

  • PXIe-5171
  • PXIe-5164
  • PXIe-5170
  • PXIe-5172

Driver

  • NI-SCOPE
  • LabVIEW Instrument Design Libraries for Reconfigurable Oscilloscopes

Issue Details

When I configure digital trigger through PXI_Trig 0 from FGEN module and set it as start trigger for PXIe-5171R, there are unwanted data from trigger point about ns ~ us length behaving like delayed trigger action. This behavior happens when acquiring data using a reconfigurable oscilloscope(PXIe-5164, 5170, 5171, 5172) with digital triggers through RTSI(PXI trigger <0..6>).
 

 
When I configure the same digital trigger and set it as start trigger for PXIe-5122, it doesn't show the same behavior.
 

How can I get rid of unwanted data when triggering?

Solution

If you know how long the delay takes, you can compensate it by adjusting trigger delay parameter of niScope Configure Digital Trigger.vi. For setting trigger delay, follow instructions below:
  1. Try acquisition with trigger delay as 0.
  2. Calculate the delay of signal compared to the trigger.
  3. Place niScope Configure Digital Trigger.vi and input the value of trigger delay when setting attributes.

Additional Information

This behavior happens because of the difference between the trigger paths and the data path.

There is no compensation for differences in delay between the digital trigger paths and the data path for a majority of NI products. Because the digital trigger path has a short delay relative to the data path, the digital trigger will be detected before the data signal is digitized by the ADC. 
This makes a certain length of data unwanted. And the length of the unwanted data is constant for a given configuration or product.
Figure 1: PXIe-5171(Reconfigurable Oscilloscope) Block Diagram, PXI Triggers connected directly through FPGA
 
  
Figure 2: PXIe-5122(non-Reconfigurable Oscilloscope) Block Diagram, PXI Triggers going along the path.

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