Rotation angle detection sensor

A rotation angle detection sensor mounted to a structure that includes a fixed part and a rotating part rotatably supported around a rotary shaft for detecting the rotation angle of the rotating part, comprising:

• a reed switch mounted to the fixed part or the rotating part of the structure perpendicular to the rotary shaft, with reeds arranged near the rotary shaft;
• and
• a flat annular magnet mounted to the rotating part or the fixed part of the structure at a specified position in the direction of the rotary shaft so that a magnetic circuit is formed with respect to the reed switch, central axis of the magnet being arranged concentrically with the rotary shaft,
• wherein the magnet is multi-pole magnetized in parallel to the central axis, and
• during the rotation of the magnet around the central axis with respect to the reed switch accompanying the rotation of the rotating part of the structure, when the same poles of the magnet are lined up in the longitudinal direction of the reed switch, both reeds of the reed switch are magnetized to the same pole, turning off the reed switch, and
• when opposite poles are lined up in the longitudinal direction of the reed switch, the both reeds of the reed switch are respectively magnetized to the opposite pole, turning on the reed switch.