I‘ve built a sensor that measures current through a wire by measuring the magnetic field, but magnetic fields from other wires are making big noise signal. Is there any way I can protect the sensor?
Just like Gary H, I beg for mercy from other posters. Folks, if the noise propagates as E-field, then Faraday cage could work. But the E-field noise doesn't interfere with magnetic (prob. Hall-effect) measurements. The noise propagates as H-field, and the shield should be made of ferromagnetic material (e.g. mild steel).
Earth’s Magnetic Field There is much uncertainty about the origin and nature of the earth’s magnetic field. A simplistic model is that of a giant bar magnet with a dipole field surrounding it (Figure 14 – 1). Measurements made of the orientation and strength of the magnetic field in thousands of locations around the earth suggest the bar magnet model, which is roughly spherical and has lines of force plunging into the polar regions, is a good approximation of the real magnetic field. The earth’s core is thought to be largely made up of molten iron, which might be the source of the field. Siesmic studies indicate that the inner core is solid and the outer core is liquid. The inner core is above the Curie temperature, so it cannot contribute to the Earth’s magnetic field. Modern theories suggest the magnetic field is caused by flow of material in the outer core which generates a flow of electrical current, which probably also contributes to the formation of an electromagnetic field.
Mercy, I don't know where some of these other posters get their info, but the only way to actually shield magnetic fields is to use superconductor material. But the practical way is to use a ferromagnetic material, such as steel or even better, mu metal. It doesn't actually shield, but what it does do is provide a very low reluctance path for flux, keeping it away from the shielded object. Mu metal is used to shield CRTs, for example.
