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The d Arsonval Galvanometer

المؤلف:  GEORGE A. HOADLEY

المصدر:  ESSENTIALS OF PHYSICS

الجزء والصفحة: 

2025-12-11

603

The d'Arsonval Galvanometer. Another principle used in the construction of galvanometers-a most important one-is employed in the instrument shown in Fig. 1. Between the poles of a horseshoe magnet placed vertically there is fixed an iron cylinder I. А coil of fine wire wound on a thin copper frame is suspended from the point A, so that it will swing freely between the cylinder and the magnet poles. When a current is sent through it, the coil becomes a magnet with its poles in a line perpendicular to the line joining the poles of the horseshoe magnet, and at once, because of the influence of the horseshoe magnet, it is deflected. The controlling force is the torsion of the wire supporting the coil. The readings are taken either from a pointer and a scale, or from the reflection of a fixed scale from a mirror fastened to the coil at the point C. This instrument has the advantage of being dead beat; that is, it will come to rest quickly without vibrations.

Figure 2 shows how the d'Arsonval principle is applied in a commercial voltmeter. The wire suspension is replaced by a spiral spring which serves to carry the current and control the position of the pointer. The coil is at right angles to the pointer and its axis is held between jeweled pivots. The magnetic field is strengthened by soft iron pole pieces bolted to the magnet and nearly surrounding the coil.