Harmonic distortion analyzers

Harmonic distortion analyzers:

Harmonic distortion:

When we give a sinusoidal signal input to any electronic instrument there should be output in sinusoidal form, but generally the output is not exactly the replica of input, because of various types of distortion that my occur.

Distortion is occur due to inherent non-linear characteristics of different components used in electronic circuit. Nonlinear behavior of electronic component introduces harmonics in the output waveform and the resultant distortion is often referred as harmonic distortion.

Types of harmonic distortion:

1)    Frequency distortion:

This type of distortion occurs in amplifiers because of amplification factor of amplifier is different for different frequencies.

2)    Amplitude distortion:

It occurs because amplifier introduces harmonic of fundamental of input frequency. Harmonics always generates distortion in amplitude. E.g. when amplifiers are overdriven it clips the waveform.

3)    Phase distortion:

This distortion occurs due to energy storage elements in the system which causes the output signal to be displaced in phase with the input signal. Signals with different frequencies will be shifted by different phase angles.

4)    Intermodulation distortion:

This type of distortion occurs as a consequence of interaction or heterodyning of two frequencies, giving an output which is sum or difference of the two original frequencies.

5)    Cross-over distortion:

This type of distortion occurs in push-pull amplifiers on account of incorrect boas levels as shown in figure.

cross over distortion
cross over distortion

Total harmonic distortion (THD):

1

In a measurement system noise is read in addition to harmonics and the total waveform consisting of harmonics, noise and fundamental is measured instead of fundamental alone

2

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Heterodyne Wave Analyzer

Heterodyne Wave Analyzer:

Introduction:

Analysis of the waveform means determination of the values of amplitude, frequency and sometime phase angle of the harmonic components.

A wave analyser is an instrument designed to measure relative amplitude of signal frequency components in a complex waveform .basically a wave instruments acts as a frequency selective voltmeter which is tuned to the frequency of one signal while rejecting all other signal components.

It is well known that any periodic waveform can be represented as the sum of a d.c. component and a series of sinusoidal harmonics. Analysis of a waveform consists of determination of the values of amplitude, frequency, and sometime phase angle of the harmonic components. Graphical and mathematical methods may be used for the purpose but these methods are quite laborious. The analysis of a complex waveform can be done by electrical means using a band pass filter network to single out the various harmonic components. Networks of these types pass a narrow band of frequency and provide a high degree of attenuation to all other frequencies.

A wave analyzer, in fact, is an instrument designed to measure relative amplitudes of single frequency components in a complex waveform. Basically, the instrument acts as a frequency selective voltmeter which is used to the frequency of one signal while rejecting all other signal components. The desired frequency is selected by a frequency calibrated dial to the point of maximum amplitude. The amplitude is indicated either by a suitable voltmeter or CRO.

This instrument is used in the MHz range. The input signal to be analysed is heterodyned to a higher IF by an internal local oscillator. Tuning the local oscillator shifts various signal frequency components into the pass band of the IF amplifier. The output of the IF amplifier is rectified and is applied to the metering circuit. The instrument using the heterodyning principle is called a heterodyning tuned voltmeter.

The block schematic of the wave analyser using the heterodyning principle is shown in fig. above. The operating frequency range of this instrument is from 10 kHz to 18 MHz in 18 overlapping bands selected by the frequency range control of the local oscillator. The bandwidth is controlled by an active filter and can be selected at 200, 1000, and 3000 Hz.

Block schematic of a heterodyne wave analyser
Block schematic of a heterodyne wave analyser

 

Applications of Wave Analyzers:

Wave analyzers have very important applications in the following fields:

1)      Electrical measurements

2)      Sound measurements and

3)      Vibration measurements.

The wave analyzers are applied industrially in the field of reduction of sound and vibrations generated by rotating electrical machines and apparatus. The source of noise and vibrations is first identified by wave analyzers before it can be reduced or eliminated. A fine spectrum analysis with the wave analyzer shows various discrete frequencies and resonances that can be related to the motion of machines. Once, these sources of sound and vibrations are detected with the help of wave analyzers, ways and means can be found to eliminate them.

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Signal waveform analysing instruments

Signal waveform analyzing instruments :

Waveform Analyzing Instruments:

Introduction:

The analysis of electrical signals is used in different applications. The different instruments used for signal analysis are wave analyses, distortion analysers, spectrum analysers, audio analysers, and modulation analysers.

All signal analysis instruments measure the basic frequency properties, but they use different techniques to do so. A spectrum analyser sweeps the signal frequency band and displays a plot of amplitude versus frequency. It has operating range of 0.02 Hz to 250 GHz. A wave analyser is a voltmeter which measures the amplitude of a signal frequency within a band of about 10 Hz – 40MHz.

A) Wave Analysers :

Analysis of the waveform means determination of the values of amplitude, frequency and sometime phase angle of the harmonic components.

A wave analyser is an instrument designed to measure relative amplitude of signal frequency components in a complex waveform .basically a wave instruments acts as a frequency selective voltmeter which is tuned to the frequency of one signal while rejecting all other signal components.

Types of wave analysers:

There are two types of wave analysers, depending upon the frequency ranges used,

a) Frequency selecting wave analyser.

b) Heterodyne wave analyser.

B) Harmonic distortion analyser :

The application of the sinusoidal input signal to an electronic device , such as amplifier should result in generation of a sinusoidal output waveform .generally the output is not exactly as the input i.e. it is not exactly sinusoidal because of various types of distortion may occur. Non linear behavior of circuit elements introduces harmonics in the output waveform and the resultant distortion is often referred as harmonic distortion.

Types of distortion analyzer :

1)      Frequency distortion

2)      Phase distortion

3)      Amplitude distortion

4)      Intermodulation distortion

5)      Cross-over distortion.

C) Spectrum analyzers :

A spectrum analyzer measures the magnitude of an input signal versus frequency within the full frequency range of the instrument. The primary use is to measure the power of the spectrum of known and unknown signals. The input signal a spectrum analyzer measures is electrical, however, spectral compositions of other signals, such as acoustic pressure waves and optical light waves, can be considered through the use of an appropriate transducer.

Types of Spectrum analysers :

Spectrum analyzer types are dictated by the methods used to obtain the spectrum of a signal. There are 1)swept-tuned and

2) FFT based spectrum analyzers.

D) Audio Analyser

An Audio Analyser is a test and measurement instrument used to objectively quantify the audio performance of electronic and electro-acoustical devices. Audio quality metrics cover a wide variety of parameters, including level, gain, noise, harmonic and intermodulation distortion, frequency response, relative phase of signals, interchange crosstalk, and more. In addition, many manufacturers have requirements for behavior and connectivity of audio devices that require specific tests and confirmations.

Audio analysis requires that the device under test receive a stimulus signal of known characteristics, with which the output signal (response) may be compared by the analyzer in order to determine differences expressed in the specific measurements. This signal may be generated or controlled by the analyzer itself or may come from another source (e.g., a recording) as long as characteristics relative to the desired measurement are defined.

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