Low Frequency (LF) Measuring System measures and simulates disturbances in the 230V/50Hz and 115V/60Hz public power supplies.

Emission

Harmonics
The increasing use of electronic equipment fitted with switch mode power supplies has led to an increase in distortion of the public power supply. Such loads draw non sinusoidal current, which contains harmonic frequencies at multiples of the 50Hz and 60Hz supply frequencies. This can lead to significant currents flowing in the neutral conductor resulting in cable and transformer overheating. This is also known as "phantom power" because it has to be transported through cables and transformers, but is not useful.

Flicker
Small variations in the mains supply voltage, caused by fluctuating currents interacting with the mains impedance, influence the light intensity of an incandescent bulb. Light intensity fluctuates as a square of the RMS voltage. These cyclic fluctuations called "flicker" are not noticed by the human eye but are registered by the brain, causing annoyance and increased stress. Power factor correction is a simple means of reducing flicker.

Immunity

Harmonics
Non linear loads connected to the public power supply generate harmonic and interharmonic currents which are transmitted throughout the power network to other equipment. Mains networks are also used to transmit control and monitoring signals. It is necessary to ensure that these unwanted frequency components do not cause disruption to control or measurement units.

Voltage variation
Changes in load conditions on the public power main, can cause voltage deviations both in a positive (overvoltage) and negative (undervoltage) direction. Equipment must be capable of maintaining normal operation during such deviations.

Ripple on DC power supplies
It is quite common for mains adapters to deliver an unregulated DC voltage. Normally this is not a problem as energy storage elements in the device being powered compensate for voltage fluctuations.