High-Speed Digitizers

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Pre-triggered samples seen even though reference-position and trigger delay set to 0

I am able to acquire data from NI-5160 2ch digitizer.

However, I am still finding it difficult to understand some concepts of High Speed Digitizer even after going through the help manual.

My goal is to collect data once the 5160 sees a trigger. Trigger is supplied by a high-precision pulse generator. The trigger width is 5ns and the delay between the trigger and pulse output is almost 0. So I can safely say that the rising edge of the trigger and pulse coincides.

  1. My goal is to start collecting data from the point the digitizer sees a trigger, which naturally I assumed would start at 0th position given the fact that I set the reference-position to 0.0% and trigger-delay  as 0.0sec. The following are my observations:
    1. Why does the digitizer still capture pre-trigger samples even though it is configured to use 0.0% reference position ?? Also the trigger delay is set to 0.0sec.
    2. Setting reference position to 0.0% still gives me pre-triggered data. Which is fine. But I want to know how to precisely calculate how many samples out of  (for example) 100000 record length belongs to pre-trigger.
    3. What's is mathematical relationship between Record Length and Sampling rate? If I choose 512MS/sec, it automatically goes to the next legal sampling rate: 6.25MS/sec. Which is fine, but how do I estimate these numbers with math before hand?

The following figure shows when the reference position and trigger delay for the digitizer was set to 0.0.

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NI System Configuration:
- NI PXIe-1071, 4-Slot 3U PXI Express Chassis , 1 GB/Slot throughput, Part Number: 781368-01
- NI PXIe-PCIe8381,x8 Gen2 MXI-Express for PXI Express Interface,3m, Part Number: 782522-01
- PXIe-5160 PXI Oscilloscope, 500 MHz, 10 bits, 2.5 GS/s, 2 Channels, 64 MB, Part Number: 782621-01
- Astronics PXIe-1209 2-Channel, 100 MHz PXI Pulse Generator, Part Number: 785033-01
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Hi 

One doubt, are you using the NI-SCOPE soft front panel? I think this is a good option to play with the triggers! 

Also, you can search examples that are shipped with LabVIEW, you can go to find examples, hardware input and outputs, modular instruments, NI scope, you could probably check the niScope EX multi device configured acquisition. 

Actual Record Length Changes with Requested Sample Rate When Using NI-SCOPE , this is a good KB.

Some useful information:

Triggering

Oscilloscope Triggering

Graphical Digitizer Example

 

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