GEAR TOOTH SENSOR WITH SINGLE MAGNETORESISTIVE BRIDGE
First Claim
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1. A method to measure rotational speed of a toothed wheel whose teeth include ferromagnetic material, comprising:
- providing at least two permanent magnets;
disposing said permanent magnets so as to form a zero field region;
placing in said zero field region an even number of MR (magneto-resistive) devices divided into equal-sized first and second groups;
arranging for said first group to be immersed in a different magnetic environment from that in which said second group is immersed, whereby said permanent magnets and said MR sensors, including said magnetic environments, together form a rotational speed detector; and
then placing said rotational speed detector near said toothed wheel whereby, when said toothed wheel rotates, a differential signal taken between said first and second groups of MR detectors may be used to determine at what rate teeth from said toothed wheel pass by said rotational speed detector.
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Abstract
The invention discloses a rotation sensor suitable for gear wheels. MR (magneto-resistive) sensors are placed inside a zero field region generated by at least two permanent magnets. Said sensors are divided into two groups that are immersed in different locally generated magnetic environments. A differential signal taken between the two groups then senses the movement of the wheel'"'"'s teeth. A single wafer method for manufacturing the device is also briefly described.
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Citations
20 Claims
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1. A method to measure rotational speed of a toothed wheel whose teeth include ferromagnetic material, comprising:
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providing at least two permanent magnets; disposing said permanent magnets so as to form a zero field region; placing in said zero field region an even number of MR (magneto-resistive) devices divided into equal-sized first and second groups; arranging for said first group to be immersed in a different magnetic environment from that in which said second group is immersed, whereby said permanent magnets and said MR sensors, including said magnetic environments, together form a rotational speed detector; and then placing said rotational speed detector near said toothed wheel whereby, when said toothed wheel rotates, a differential signal taken between said first and second groups of MR detectors may be used to determine at what rate teeth from said toothed wheel pass by said rotational speed detector. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A detector to measure rotational speed of a toothed wheel whose teeth include ferromagnetic material, comprising:
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at least two permanent magnets; a zero field region generated by said permanent magnets; located in said zero field region, an even number of MR (magneto-resistive) devices arranged in first and second groups; said MR devices being inter-connected as a Wheatstone bridge in which said first and second groups each contain a first MR device whose input comes from an external source and whose output is connected to a first output of said Wheatstone bridge, and a second MR device whose input comes from an MR device not in said second MR device'"'"'s group and whose output is connected to a second output of said Wheatstone bridge; and a magnetic shield for all members of said first group, there being no magnetic shielding for all members of said second group. - View Dependent Claims (12, 13, 14)
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15. A detector to measure rotational speed of a toothed wheel whose teeth include ferromagnetic material, comprising:
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at least two permanent magnets; a zero field region generated by said permanent magnets; located in said zero field region, an even number of MR (magneto-resistive) devices arranged in first and second groups; said MR devices being inter-connected as a Wheatstone bridge in which said first and second groups each contain a first MR device whose input comes from an external source and whose output is connected to a first output of said Wheatstone bridge, and a second MR device whose input comes from an MR device not in said second MR device'"'"'s group and whose output is connected to a second output of said Wheatstone bridge; all members of said first group being immersed in a first locally generated magnetic field having a first direction; and all members of said second group being immersed in a second locally generated magnetic field having a second direction that is different from said first direction. - View Dependent Claims (16, 17, 18, 19, 20)
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Specification