Importance

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Abstract

A linear position encoder is provided which is not affected by ambient light, smoke, moisture, particulate matter, and also not affected by electrical interference such as may be caused by stray fields or permanent magnets or magnetic particles. The encoder comprises a linear scale having an excitation loop disposed along the length of the scale and having electrical terminals preferably disposed at one end of the scale. An alternating current is applied to the excitation loop to create an alternating magnetic field. At least one periodic conductive pattern is provided on an outer side of the excitation loop. The periodic pattern has electrical terminals preferably at the same end of the scale as the terminals of the excitation loop. A sensor is provided on a small printed circuit card that is movable in relation to the scale. The card has a pickup loop which receives energy coupled from the scale excitation loop and which induces current in the periodic pattern. The resulting magnetic field is spatially modulated and motion of the sensor in relation to the scale amplitude modulates the output signals to provide an output indication of linear travel along the scale.

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First Claim