Galvanometer Brass Glass England '800

Compass of Tangents

It is the simplest example of a galvanometer, that is a device that measures the intensity of the current by means of the magnetic field created by it. The body of the luminaire, supported by three leveling screws, consists of a thick brass ring, whose external diameter is 200 mm, on which a circular scale is engraved. Inside the ring can rotate a disk, also made of brass and of the same thickness, which supports, in the points where it is crossed, a vertical circular frame, of the same metal. The rotation of the disc inside the ring is facilitated by two small handles vertically fixed to it; its position is read on the external scale, in correspondence with two diametrically opposite incisions, marked between two pairs of clamps, placed on the sides of the vertical frame. On the periphery of the frame, two systems of turns are wound in a groove; each of the two spools thus obtained is connected to two clamps. Since the two circuits have very different resistances, by joining them in series or in parallel the compass can be used to measure currents of very different intensity. From the disc, in the area immediately inside the coils, protrudes a ring that holds an annular aluminum limbus inside, which carries a scale with divisions that mark the degrees; the ring is closed by a lid with a glass plate through which the inside of the compass can be observed.