Samples acquired before rising edge of trigger

[iclapa]

Hi,

I'm developping a c program for the PXI 4472 acquistion device

on opensuse 11.4 (linux 2.6.34)

I want to start an acquisition on the rising edge of a pulse signal connected to the digital trigger input.

[iclapa]

[next part of the message (sorry)]

The test program I wrote (see attached file) is a modified version of one of the example programs coming with nidaqmx packages. Data samples are stored as an ASCII file in a text file.

On the hardware side, a pulse signal is connected both to the digital trigger input and to one of the analog inputs (channel ai0). It allows an easy way to see the pulse signal triggering the acquisition.

I notice the acquisition always starts about 40 samples  before the rising edge of the signal. This behaviour is similar when triggering on the falling edge of the pulse.

I would like to know why and how to start the acquistion right on the rising edge.

Thank you for your support

A.C

[Brad_K]

Hi iclapa,

DSA devices use delta-sigma ADCs, which have an inherent filter delay. Here's a knowledgebase that shows how to compensate for this by discarding samples that were acquired before the trigger: Why Is My Data Delayed When Using DSA Devices?

Brad

[iclapa]

Hi Brad,

Thank you very much for the clarifications!

Have a nice day!

Amandine.

[iclapa]

Hi Brad,

Thank you very much for the clarifications!

Have a nice day!

Amandine.