AS/NZS 61000.4.7:2012 PDF – Electromagnetic compatibility (EMC) Part 4.7: Testing and measurement techniques—General guide on harmonics

1 Scope

This part of IEC 61 000 is applicable to instrumentation intended for measuring spectral components in the frequency range up to 9 kHz which are superimposed on the fundamental of the power supply systems at 50 Hz and 60 Hz. For practical considerations, this standard distinguishes between harmonics, interharmonics and other components above the harmonic frequency range, up to 9 kHz. This standard defines the measurement instrumentation intended for testing individual items of equipment in accordance with emission limits given in certain standards (for example, harmonic current limits as given in IEC 61 000-3-2) as well as for the measurement of harmonic currents and voltages in actual supply systems. Instrumentation for measurements above the harmonic frequency range, up to 9 kHz is tentatively defined (see Annex B). NOTE 1 This document deals in detail with instruments based on the discrete Fourier transform. NOTE 2 The description of the functions and structure of the measuring instruments in this standard is very explicit and meant to be taken literally. This is due to the necessity of having reference instruments with reproducible results irrespective of the characteristics of the input signals. NOTE 3 The instrument is defined to accommodate measurements of harmonics up to the 50th order.

4 General concepts and common requirements for all types of instrumentation

4.1 Characteristics of the signal to be measured

Instruments for the following types of measurement are considered: a) harmonic emission measurement, b) interharmonic emission measurement, c) measurements above harmonic frequency range up to 9 kHz. Strictly speaking the (Fast) Fourier Transform produces accurate results for steady state signals only. Signals whose amplitudes vary with time cannot be described correctly by their harmonic components only. In order to obtain reproducible harmonic emission analysis results when measuring products with fluctuating power, and thus fluctuating fundamental current and possibly fluctuating harmonic current levels, a combination of averaging techniques and sufficiently long measurement cycles can be used. This standard therefore provides a simplified method employing specific averaging methods (see 5.5.1 ). Furthermore, a test observation period, long enough to obtain successive measurement results that are within acceptable tolerance levels is specified in the harmonic emission standards referring to this standard.

The time window shall be synchronised with each group of 1 0 or 1 2 cycles according to the power system frequency of 50 Hz or 60 Hz. The time between the leading edge of the first sampling pulse and the leading edge of the ( M +1 )th sampling pulse (where M is the number of samples; see 3.5.1 ) shall be equal to the duration of the specified number of cycles of the power system, with a maximum permissible error of ±0,03%. Instruments including a phase- locked loop or other synchronisation means shall meet the requirements for accuracy and synchronisation for measuring at any signal frequency within a range of at least ±5% of the nominal system frequency. However, for instruments having integrated supply sources, so that the source and measurement systems are inherently synchronised, the requirement for a working input frequency range does not apply, provided the requirements for synchronisation and frequency accuracy are met.