A Bridge Method for Determining the Motional Characteristics of Permanent-Magnet Movable-Coil Instrument Mechanisms

The instrument mechanism is expressed in terms of an equivalent electric network, and the apparent electrical parameters determined by a-c bridge methods. The extracted parameters are: the apparent series resistance, the apparent damping resistance, the undamped period, and the periodicity at which the phase angle of reactance to the shunt resistance is -45 degrees. From these the periods and damping coefficients can be calculated. By including the d-c deflection sensitivity of the instrument the moment of inertia and the restoring torque gradient also can be calculated.