Improved linear variable differential transformer for high-accuracy posotion survey

Abstract

A transducer that reduces noise, increases sensitivity, and improves the time response of a linear variable differential transformer (LVDT). The device replaces the primary coil and the high permeability ferromagnetic core of conventional LVDTs with a primary wound around a moving non-ferromagnetic core. In addition to reducing or eliminating Barkhausen noise, this approach reduced or eliminated a number of other undesirable effects in conventional LVDTs including excessive eddy current heating in the core, non-linearities associated with high permeability materials and the length scale of the flux circuit. These improvements are coupled with improved LVDT signal conditioning circuitry. The device is also an actuator and may be used to convert differential voltages into force. Devices with these improvements have numerous applications, including molecular force measurements, atomic force microscopy and manipulation technology, lithographic manufacturing, nanometer scale surface profiling and other aspects of nanotechnology.

Description

technical field [0001] The present invention relates to a number of devices that convert extremely small mechanical displacements (down to the sub-nanometer scale) into differential voltages (and vice versa). Background technique [0002] In the early part of the last century, one type of position sensor utilized to convert mechanical displacement to differential voltage (and vice versa) was the Linear Variable Differential Transformer (LVDT). exist figure 1 A conventional commercial LVDT (part number 50-00-005XA, Seotech Inc., North Hills, PA, USA) with a moving, ferromagnetic core 1 differentially coupling flux from a primary coil 2 to two secondary coils is described in stage coils 3 and 4. Current is driven by an oscillator 5 through the primary coil. As the core position changes relative to the secondary coil, the magnetic flux coupling to the two secondary coils changes. These voltages are amplified by a differential amplifier 6 and signal conditioning electronics ...

AI Technical Summary

Problems solved by technology

However, for this and other reasons, this design shares these limitations of previous LVDTs in its large length scale, with even less sensitivity than previous designs

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