Harmonic distortion meters are instruments that measure harmonic distortion or phase position. Harmonic distortion is a common problem in power systems, electronic ballasts, data processing equipment and adjustable speed drives. In communications applications, harmonic distortion meters and phase meters are used to determine when the original frequency transmitted is split into multiple frequencies due to irregularities in the line.

Harmonic distortion meters are important for analyzing the quality of power coming into a system and for determining what is causing the problem. Before any mitigation techniques can be used, the source of the problem must be identified. Some harmonic distortion meters analyze the total harmonic distortion (THD) as well as individual harmonics that may be present in a system. THD is often a problem in audio equipment, especially loudspeakers. Software packages that are designed for a harmonic distortion meter or phase meter allow the storage and manipulation of measurement data.

Harmonic distortion meters monitor the change in phase of a waveform. Special types of phase meters include phase sequence indicators, phase angle volt meters, and phase rotation meters. A three phase sequence indicator is used to find the proper sequence of a power system with three wires. A phase angle voltmeter is used in rotational and linear position measurements. Phase angle voltmeters may also measure impedance and power as well as harmonics and phase over a particular frequency range. A phase rotation meter measures the rotation direction of motor shafts and ensures that motor is correctly wired. Phase rotation meters also indicate a phase orientation of clockwise or counterclockwise.

Suppliers of harmonic distortion meters are located across the United States and around the world. They conform to a variety of regulatory requirements and quality standards.