(under subclass 244) Subject matter wherein the apparatus to sense a magnetic field is a stationary electrical coil placed in a changing magnetic field to be tested, and the apparatus to indicate the sensing of the field is connected to the coil whereby the changing magnetic field induces in the coil a voltage proportional to the number of turns of the coil and
the time it takes the changing field to make a complete change.
(1) Note. The tested changing field may be the movement of a magnetic core in the magnetic field tested, the magnetic core being moved relative to the sensing coil.
(2) Note. The sensing coil may include a ferromagnetic core.
