Magnetic field indicator, model MFI-3 made by KBR Magneto.
A special layer with deposited magnetic particles is used, and images are “recorded” on it magnetically. If a large magnetic field is applied to the layer (e.g. exceeding 100 kA/m) then images are permanently erased. It is a single-use device.
Such indicators are used for protection of meters against the theft of electricity or water:
- Magnetic field indicator, Wskaźnik pola magnetycznego MFI-3, Magneto.pl, {accessed 2021-06-12}
magneto_field_indicator_mfi-3_e-m.jpg
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S. Zurek, Encyclopedia Magnetica, CC-BY-4.0
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