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.