Harmonic Distortion Meter Constructed around PIC18F2550

The project was built and designed to measure the quality of AC voltage using a harmonic distortion meter based on PIC18F2550.

The meter is using 3rd harmonic distortion for measuring the quality of AC supply by comparing the distortion value to fundamental frequency. A PIC18F2550 project board and the full wave rectifier front-end circuit are used to build the meter. Through the step down isolation transformer, the 220VAC power line is measured where the input signal to the 10-bit ADC is full wave rectified. The DFT calculation is performed by the software where the amplitude of the 3rd harmonic and the fundamental frequency is obtained.

The ratio of the amplitude of the 3rd harmonic to the fundamental frequency is used to compute the distortion. A resulting 33% distortion is obtained when the meter was tested with the square wave signal. A reading of approximately 3% will be shown for low voltage 220VAC utility. With the appropriate signal conditioning, the meter can be applied for high voltage application.

The quantity of the Total Harmonic Distortion is used to measure the wave shape of distortion. The PIC18F2550 board receives AC signal from isolated transformer.
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