A harmonic is a sine wave with a multiple frequency of the fundamental wave. A distorted wave consists of a DC- component, the fundamental wave and its harmonics.

Harmonic analysis is resolving a distorted wave form into the fundamental component and its harmonic components. The WT-series realises this by using FFT (except for the DC-component, which is measured in DC-mode).

Sometimes, non-linear loads cause harmonic current components on the mains. Because of the non-zero impedance of the power lines this results in a distorted voltage at the neighbours. Affecting badly the electric and electronics instruments connected to the same power line.

For example, it is possible that a power supply capacitor equipment produces strange sounds, vibrates and heats-up by the harmonics current. As a result, its life time decreases, it causes to burn out or it causes malfunctioning of the equipment.

Therefore the IEC developed the regulation IEC1000-3-2, in order to protect electric equipment against the harmonic current problem.
Meanwhile, inverter- and motor manufacturers use the harmonic analysis to measure the performance of their products. Now a days, many inverters are used to drive electric motors. The inverter controls the rotating speed of the motor by varying the frequency or amplitude of the input voltage to the motor. The varied signal is a distorted waveform, so it includes harmonic components. These components also are affect the motor rotation and the motor does not rotate smoothly. This means a waste of the power and shortening the motors life time. Therefore these manufacturers analyse the harmonics.

 

The VCO outputs a sampling clock n-times the input frequency.

The FFT calculation is always based on n-data points

This table shows the relationship between the number of harmonics included and the remaining error as a percentage of the ideal waveform.

Note

• The fundamental (= first harmonic) and the higher harmonics are pure sine-waves.
• The error is measured against RMS values

Error when excluding higher harmonics (rectangular and triangular waves)