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Working of the harmonic distortion analyzer:



  • working of the harmonic distortion analyzer:


Distortion analyzer measures the total harmonic power present in the test wave rather than the
distortion caused by each component. The simplest method is to suppress the fundamental
frequency by means of a high pass filter whose cut off frequency is a little above the
fundamental frequency. This high pass allows only the harmonics to pass and the total harmonic
distortion can then be measured. Other types of harmonic distortion analyzers based on
fundamental suppression are as follows
1. Employing a Resonance Bridge
The bridge shown in fig 3.1 is balanced for the fundamental frequency, i.e. L and C are tuned to the
fundamental frequency. The bridge is unbalanced for the harmonics, i.e. only harmonic
power will be available at the output terminal and can be measured. If the fundamental
frequency is changed, the bridge must be balanced again. If L and
CCCCCCCCCCCCCCCCCC are fixed components, then this method is suitable only
when the test wave has a fixed frequency. Indicators can be thermocouples or square
law VTVMs. This indicates the rms value of all harmonics. When a continuous
adjustment of the fundamental frequency is desifrequency is desired a Wien bridge
arrangement is used as shown in fig 3.2.














2. Wien’s Bridge Method
The bridge is balanced for the fundamental frequency. The fundamental energy is
dissipated in the bridge circuit elements. Only the harmonic components reach the output
terminals .The harmonic distortion output can then be measured with a meter. For
balance at the fundamental frequency
C1=C2=C, R1=R2=R, R3=2R4.
3. Bridged T-Network Method
Referring to the fig 3.3 the L and C’s are tuned to the fundamental frequency, and R
is adjusted to bypass fundamental frequency. The tank circuit being tuned to the fundamental
frequency, the fundamental energy will circulate in the tank and is bypassed by the resistance.
Only harmonic components will reach the output terminals and the distorted output can
be measured by the meter. The Q of the resonant circuit must be at least 3-5.
One way of using a bridge T-network
is given in Fig. 3.4 The switch S is first
connected to point A so that the
attenuator is excluded and the
bridge T-network is adjusted for full
suppression of the fundamental
frequency, i.e. Minimum output
indicates that the bridged Tnetwork
is tuned to the
fundamental frequency
and that
fundamental frequencies
is fully suppressed.

The switch is next connected to terminal B, i.e. the bridge T- network is excluded. Attenuation is
adjusted until the same reading is obtained on the meter. The attenuator reading indicates the
total rams distortion. Distortion measurement can also be obtained by means of a wave analyzer,
knowing the amplitude and the frequency of each
component, the harmonic distortion can be calculated.
However, distortion meters based on fundamental
suppression are simpler to design and less expensive
than wave analyzers. The is advantage is that 1give
only the total distortion and not the amplitude of
individual distortion components.



Working of the harmonic distortion analyzer: Working of the harmonic distortion analyzer: Reviewed by haru on March 17, 2012 Rating: 5

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