Electrical Power Systems Technology

Power Measurement Equipment 61

Many meters employ an analog movement called the d’Arsonval, or

moving-coil, type. The basic operational principle of this type of movement

is shown in Figure 3-2. The pointer or needle of the movement remains

stationary on the left portion of the calibrated scale until a current flows

through the electromagnetic coil that is centrally located within a perma-

nent magnetic field. When current flows through the coil, a reaction be-

tween the electromagnetic field of the coil and the stationary, permanent

magnetic field develops. This reaction causes the hand (pointer) to deflect

toward the right portion of the scale. This basic moving-coil meter move-

ment operates on the same principle as an electric motor. It may be used

for either single-function meters, which measure only one quantity, or for

Figure 3-1. Moving-coil meter movement for analog meters (Courtesy Triplett

Corp.)