Influence of the mains frequency 50/60 Hz

Stationary electrical devices are usually supplied directly or via UPS from the building supply. There, 110 … 240 V AC is common worldwide, although 50 Hz is used as the mains frequency in many countries and 60 Hz in some. Power supplies/voltage transformers deliver a highly smoothed DC power on the output side, e.g., when converting 230 V AC to 24 V DC. However, in areas where supply lines are laid, 50 or 60 Hz radiation remains, which affects grounding/FE/PE, metallic structures, communication and signal lines – if no shielding measures have been taken. Since building PE/FE is therefore usually also exposed to the base frequency (and its harmonics) as a selected interference sink, this interference signal can in turn enter the signal flow via the PE connection connected to an ELM3xxx terminal, for example.
To eliminate/attenuate this interference signal from analog signals, analog input devices have at least a (digital) 50 and 60 Hz filter.