TABLE OF CONTENTS In these transducers, the transduction mechanism is one where the self-inductance of a single coil or the mutual inductance between two coils is changed by a measurand. In general, the measurand could be a linear or rotary displacement, pressure, force, torque, vibration velocity, and acceleration. The inductance changes are brought about by the movement of a concentric magnetic core.
The inductance of a single coil increases as the core is inserted in the coil and reaches a maximum value when it is centered on the coil length. Similarly, two separate coils L 1 and L 2 wound on the same bobbin can also be used as a displacement transducer. Any measurand that moves the core directly through a summing device will produce a change in the impedance of the coils that is proportional to the magnitude of the measurand. The coils can be used as the adjacent arms of an impedance bridge. Since L 1 increases by the same amount that L 2 decreases, or vice versa, the bridge output will be doubled.
A variation of the inductive transducer, shown schematically in Fig. 5.6a, is known as the linear variable differential transformer (LVDT).18 ,19 This transducer consists of a primary coil L 1, two interconnected coils L 2, L 3, and a common magnetic core. The coils are wound on a hollow nonmagnetic glass-filled nylon tube and the core slides coaxially inside the tube. The excitation frequency for...
