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Using an NI Digitizer for Frequency Counter Measurements

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Overview

This example demonstrates how to use an NI High-Speed Digitizer to accurately and efficiently measure the frequency of a signal. A small waveform acquired from a high-speed digitizer and signal processing algorithms provided in NI LabVIEW can be used to accurately measure signal frequency. While several factors can affect overall accuracy (see below), frequencies above 50 MHz have been acquired and measured with better than 1 ppm accuracy in under 100 milliseconds. Multiple NI digitizers can also be synchronized to expand the number of frequency outputs being tested.

Downloads

Filename: fast_tone_detect-no_hardware.vi
Requirements: View

Filename: ni_scope-fast_tone_detect.vi
Requirements: View

Using the Extract Single Tone Information function this example isolates the tone with the highest amplitude and reports its frequency.  The accuracy of the frequency measurement can be calculated by supplying a signal with a known frequency and setting the Expected Frequency on the front panel.

In the case where a test frequency is not available, this example enables you to simulate a signal using one or more sine tones and noise.  The example also measures the amount of time required to perform the frequency measurement to determine feasibility of its use within a larger application.

Note that several factors can affect the accuracy of the measurement, including:

  • Stability of the tone being measured
  • Noise in the tone
  • Accuracy of the digitizer being used
  • Speed of the machine performing the processing

Two Examples are included, NI-Scope - Fast Tone Detect and Fast Tone Detect - No Hardware.

The first example, NI-Scope - Fast Tone Detect, acquires a signal from a High-Speed Digitizer and requires that you have the NI-Scope driver installed.  The latest driver can be found on the  Drivers and Updates page.  This example also includes the ability to simulate a signal.

The second example, Fast Tone Detect - No Hardware requires no hardware as its name suggests. 

Requirements


Filename: fast_tone_detect-no_hardware.vi

Software Requirements


Application Software: LabVIEW Full Development System 7.1
Language(s): LabVIEW

Hardware Requirements


Hardware Group: High-Speed Digitizers (Scopes)
Hardware Model: PCI-5102, USB-5133, PCI-5112, PCI-5114, PCI-5122, PCI-5124, PCI-5142, PCI-5152, PCI-5911, PCI-5922, PXI-5102, PXI-5105, PXI-5112, PXI-5114, PXI-5122, PXI-5124, PXI-5142, PXI-5152, PXI-5922, USB-5132, PCI-5105
Driver: NI-Scope 3.4

 
Filename: ni_scope-fast_tone_detect.vi

Software Requirements


Application Software: LabVIEW Full Development System 7.1
Language(s): LabVIEW

 
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This example program (this "program") was developed by a National Instruments ("NI") Applications Engineer. Although technical support of this program may be made available by National Instruments, this program may not be completely tested and verified, and NI does not guarantee its quality in any way or that NI will continue to support this program with each new revision of related products and drivers. THIS EXAMPLE PROGRAM IS PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND AND SUBJECT TO CERTAIN RESTRICTIONS AS MORE SPECIFICALLY SET FORTH IN NI.COM'S TERMS OF USE (http://ni.com/legal/termsofuse/unitedstates/us/).