Ever since the first generators, harmonics have been a part of power systems. However, we now live in an era of power that is defined by non-linear loads. Equipment for powering computers, electronic ballasts, and VFDs are among the electronic power supplies that are used now more than ever. Unchecked harmonic distortion in these electrical equipment systems can result in damage and hazards such as overheating. Not only does this affect power quality, but it can become costly to fix. The question then becomes: do you know how to correctly measure the waveforms of your equipment while taking harmonic distortion into account?
All electromagnetic current meters function on the basis that the intensity of the magnetic field around a coil is proportional to the amount of current flowing through it. Whether the meter you are using is alternating current (AC) or direct current (DC), knowing what to expect from the different meter movements is essential for correct calibration and accurate measurements.
For circuit operation, the variations between de and ac functions are not too dissimilar. For de signal voltages, the individual stages of the instrument are directly coupled. Direct coupling can also be used for ac voltage signals, but typically capacitors are used to pass only the ac signal voltages from one stage to another. The test indications for ac must be handled slightly differently because of the nature of ac waveforms and the different ways of describing their levels. One ac wave has average, effective (RMS), and peak values. The analog meter movement responds to the average ac value, but we all use the effective or RMS value to describe a waveform, such as 120-V ac line power. The ac meter is calibrated for the effective value, even though it reacts to the average value.