‘Harmonics’ as defined by EMC standards refers to harmonics of the 50 or 60Hz mains supply that are imposed on the current drawn from the supply by the product. Many products impose a non-linear load on the mains which results in current being taken for only part of the voltage cycle. The result is that power is taken at higher ‘harmonic’ frequencies for which the mains distribution is not designed. Even though the amount created by each product may be small, the overall effect of many 1,000s on the local electricity supply network can affect the reliability of the supply network.
The EMC Directive now includes limits on harmonics which are mandatory on all products connected to the public mains supply. The standard for products rated at up to 16A/phase is IEC61000-3-2. The AC2000A is fully compliant with this standard and will provide all the measurements necessary to complete the compliance assessment.
Measurement of harmonics includes a requirement for the incoming mains to be itself free from harmonic content (<0.1% THD) as this may otherwise affect the accuracy of any measurements. The AC1000A is a clean power source that will provide a pure sine wave with the required low THD for loads up to 1kW.
This same instrument, also includes flicker measurements as required by IEC61000-3-3, to include inrush current measurement.
Flicker is a measure applied to products that draw relatively heavy current repetitively at a rate between 1Hz and 25Hz. Heavy current will depress the supply voltage. Incandescent lighting is sensitive to variations in the supply voltage, so a small variation can produce a significant variation in light output. A variation in the 1 – 25Hz range causes flicker, which can induce epileptic episodes in those who are susceptable. Hence the introduction of the standard to limit the effect. Note that any product (a) not drawing a heavy current or (b) not capable of varying the load within the above frequency range, does not require any measure of ‘flicker’.