Eddy-current mutual-inductance transducers with high-conductivity reference plates

The design considerations of mutual-inductance devices for use in noncontacting measurements of distance are studied with special emphasis on the eddy-current type utilizing ¿perfectly¿ conducting metal reference plates of infinite extent. The force on the plate due to the exciting current, typical schematic circuits used to detect the results, and the effects of rapid motion of the gauge are given. Since actual reference plates are not perfectly conducting nor infinitely extensive, some indications of the effects of finite conductivity and limited extent of reference plates are included.