The movable core transformer as a pickup for industrial telemetering systems

THE differential transformer is a transducer type of pickup in which mechanical displacement is converted into a proportional electric output by varying the mutual inductance between a primary winding and two secondary windings. The effect is a differential one so that motion of the core or rotor in one direction produces an increase in induced voltage in one secondary winding and a decrease in the other. A reversal of the direction of motion produces a reversal of the direction of change of secondary voltages. There are three basic types of differential transformers: 1. The mutual inductor type in which the flux linkage between the primary and secondary windings is varied by angular or linear displacement of the primary winding relative to the secondaries. 2. The type in which the coupling between the primary and two secondaries is differentially varied by linear or angular positioning of a short-circuited winding. 3. The movable core transformer (MCT) in which the flux linkages between the primary and each of the two secondaries is established by the position of the magnetic core. In the most common form, this device consists of a solenoid-type coil and a solid or laminated form of simple bar core mechanically linked to the primary measuring element.