Electric fields are weakened by shielding measures like conductive wallpaper, grids (Faraday cage) etc. to an extent that mostly eliminates interference. Interference which can be caused by mains-frequency magnetic fields from e.g. by power lines, elevator engines and magnetic control gear in fluorescent luminaires can be effectively avoided by reducing the magnetic fields of interference sources and appropriate distances between measuring circuit and source (e.g. control gear). Minimum distances areca. 75 cm for inductive control gear, and ca. 30 cm for electronic control gear.
This way, the maximum induction values specified by DIN VDE 0100-710 "Low-voltage electrical installations – Part 7-710: Medical locations"for ECG BSS = 4 · 10-7 Tesla = 0,4 μT for EEG BSS = 2 · 10-7 Tesla = 0,2 μT for EMG BSS = 1 · 10-7 Tesla = 0,1 μTare not exceeded.
Figure shows a measuring method for easy on-site magnetic induction measurement. EN ISO 11197 "Medical supply units" describes a block diagram for a corresponding measuring device (q.v. chapter "Medical-use rooms").