This mains noise tester allows to measure the interference and therefore the noise on a power network and to compare filtered and unfiltered systems. It operates over a frequency range of 300kHz to 700kHz. Below or above these values, an LED lights up to indicate that the value is out of range.

Using it to compare an unfiltered and a filtered system is simple: just plug the tester into the unfiltered system, set the sensitivity to 100, and then plug the tester into the filtered system to see the difference in noise.

A loudspeaker at the device makes the noise audible. The higher the noise level, the higher the sound level.