Enable Chop Measurement Feature

Publish Date: May 19, 2017 | 2 Ratings | 3.00 out of 5 | Print | Submit your review

Overview

This example demonstrates how to enable the chopping feature on NI hardware.

Table of Contents

  1. Description
  2. Requirements
  3. Steps to Implement or Execute Code
  4. Additional Information or References

 

1. Description

Chopping is a feature that can be used to remove signal path offset voltages and reduce noise. The improved measurement performance is achieved by measuring the signal twice, once normally (V0) and once with the inputs inverted (V1). These measurements are then averaged by the device to create a sample. A hardware diagram is provided in the image below.

Note: The Voffset in the diagram is not a literal voltage supply in the hardware. It is a representation for the summation of offset voltages in the signal path.


V0 represent the measurement when the multiplexer selector K is set to 0, and V1 represents the measurement when the multiplexer selector K is set to 1. This results in the measurements:
V0 = Vs(+) – Vs(-) + Voffset
V1 = Vs(-) – Vs(+) + Voffset

The negative polarity measurement (V1) is negated prior to averaging. The resulting averaged sample is:
(V0 + (-V1))/2 = ((Vs(+) – Vs(-) + Voffset) – (Vs(-) – Vs(+) + Voffset))/2 = Vs(+) – Vs(-)

The AI.Chop.Enable attribute/property can be used to enable or disable the chop feature. Refer to your device documentation on how to appropriately wire the signal source to the device in order to perform a chop measurement.

 

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2. Requirements

 Software

  • LabVIEW 2014 (or compatible)
  • NI-DAQmx 17.1 (or compatible)
    Note: The minimum required LabVIEW and NI-DAQmx version will depend on when support was introduced for the hardware. Check the corresponding User Guide for the hardware you are using to find the appropriate minimum NI-DAQmx version.

  Hardware

  • A device that supports the chop feature:
    • NI PXIe-4309

 

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3. Steps to Implement or Execute Code

In order to run this example,

  1. Open VI and select the appropriate Channel and Timing Settings.
  2. Toggle the Enable Chop button to enable/disable the Chop feature.
  3. Run the VI to perform an acquisition.

Press the Stop button to end the acquisition.

 

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4. Additional Information or References

 

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Downloads

Attachments:

enable_chop_acquisition.vi

Requirements


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