Application Note Measuring power with clamp meters There are times when one would like more from their multimeter than just a basic voltage and current measurement. Modern clamp meters are often equipped with at least some options for measuring power and power quality. They can measure voltage and current in AC or DC, analyse signal waveform through THD or crest factor, and finally even save some measurements for later analysis. Power measurements Handheld clamp meters most commonly measure the following: • Real/active power: net transfer of energy in the direction of the load, measured in watts; • Reactive power: net transfer of energy in the directions of generator, measured in volt-ampere reactive • Apparent power: vector sum of the former, whole power in the network, measured in volt-ampere • Power factor: ratio of real to apparent power, no unit; also called cos ϕ. Distortion factors are not immediately part of power measurement, but they can help evaluate losses. • Crest factor: ratio between highest and RMS value of the signal. Clamp meters often don't show it, but one needs to keep in mind it affects other measurements. • Total harmonic distortion (THD): ratio between effective values of higher harmonic components and the base one. Principle of power measurements in clamp meters Handheld instruments rarely measure power by itself, for example with thermal effect, so this article won't touch this. The clamp can be a current transformer

Measuring crest factor and THD Crest factor is the most basic way to estimate power quality, particularly commonly used in audio systems. In case of averaging multimeter (not true RMS), crest factor also estimates the error made. Even some TRMS meters are limited in their measurement by crest factor size. Total harmonic distortion is important information about network power quality. Higher harmonic content is connected to higher thermal losses, magnetic core losses, high current spikes, and similar. Sometimes, a resonance of a higher components can express itself and causes considerable trouble...

current. Its defining features are measuring whole power in an unbalanced three-phase system and measurement and logging of used energy on its own, without the use of PC. It notes the type of load in capacitive/inductive sense. METREL D.D. Measuring and Regulation Equipment Manufacturer Ljubljanska 77, SI-1354 Horjul, Slovenia T +386 (0)1 75 58 200, F +386 (0)1 75 49 226 [email protected], www.metrel.si