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A Saturable Core Reactor for Automatic Test Equipment (page 1)

Abstractó Our development of an Automated Test System (ATS) for Proximity Sensor Electronic Units (PSEUs) in the aircraft industry required the implementation of a saturable core reactor. The saturable core reactor simulates inductive proximity sensors so the ATS can measure and verify the switch points of the electronics as the sensors move between their near and far states. Though developed for PSEU testing, the presented methodology and technology may be applied to other test equipment and applications that require a saturable core reactor.

The paper begins by looking at different techniques for implementing a saturable core reactor: moving cores, switched decade boxes, gyrator circuitry and saturable core reactors. The paper presents the pros and cons of the different technologies and then focuses on the development of a saturable core reactor as the chosen technology.

The paper presents fundamental formulae used during the development of the saturable core reactor and test results for a number of developed prototypes. The presentation includes the development of a highly-accurate control loop to precisely hold the value of the controlled inductance. Finally, the paper concludes with a brief discussion of the ATS that ultimately housed the saturable core reactor.

A saturable core reactor is effectively a transformer with direct current flowing through one of the windings. This control current intentionally saturates the core of the transformer. Varying the control current moves the core along its saturation curve and hence varies the inductance seen at the other winding of the transformer. Variations in wire gauge, number of turns, core material, core geometry and air-gap geometry all affect the performance of the variable inductor.

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