2026-02-23 · Technical Insights

EMC: Why Strong Magnetic Fields Disturb Measurement and How to Pass Certification

EMC (electromagnetic compatibility) measures a device's ability both to work normally in an electromagnetic environment and not to disturb other equipment. For magnetostrictive displacement sensors EMC is especially critical — they sense position by the magnetic field of the position magnet, and an external strong magnetic field superimposes directly and disturbs the measurement. It is also a necessary review item for CE and similar certifications.

Why magnetostrictive sensors particularly dislike strong magnetic fields

The measurement depends on the axial static field that the magnet establishes on the waveguide. When a strong alternating field is present outside (for example near a high-power inverter, a large motor or a welding set), that field superimposes on the magnet field, distorts the signal received by the echo-detection circuit, and appears as jumping readings, drift or a lost echo. This is an interference source particular to magnetostriction compared with photoelectric types.

Immunity measures

Screened cable, single-end earth: use screened twisted pair for the signal cable and earth the screen at one end only (see screen earthing), to avoid earth loops introducing mains-frequency interference;
Keep away from high-current cables: run signal and power cables in separate trunking, at least 20 cm apart; where they must cross, cross at right angles;
Metal-housing screen: the electronics-head metal housing itself provides some screening; ensure the housing is fully earthed when mounting.

Emission and immunity

EMC requires not only "immunity" (not being disturbed) but also that "emission" is within limits (not disturbing other equipment). Compliant products must be laboratory-tested and obtain the corresponding certification. A site rectification case is in an EMC rectification review.

Common interference sources and countermeasures

Interference source	Effect	Countermeasure
Inverter / large motor	Strong alternating magnetic field	Distance, screening, single-end earth
Power cables in parallel	Induced crosstalk	Separate trunking, spacing ≥20 cm
Welding / switch-mode supplies	Pulse interference	Filtering, independent supply

EMC standards Germanjet uses

CE EMC tests, laboratory to ISO/IEC 17025. Emission EN 61000-6-3; immunity EN 61000-6-2; EN 61000-4-2 / 4-3 / 4-4 / 4-6 / 4-8. Certification does not replace correct shielding and cable routing on site.

Do not mix vibration figures with EMC: most profile / in-cylinder types are 15 g / 100 g to IEC 68-2-6 / 68-2-27; Series 13 is 25 g / 100 g. Installation under vibration: vibrating environments.