| 摘要 |
Disclosed is a device (1) for use in determining the rotational speed of a body. The device (1) comprises a sensor (20) for detecting the strength of a magnetic field, and a body (10) that is rotatable relative to the sensor (20) about an axis (A-A). The body (10) comprises a plurality of circumferentially spaced magnetic regions (11, 12, 13). The device (1) is arranged so that, during rotation of the body (10) relative to the sensor (20), the maximum strength detectable by the sensor (20) of a first magnetic field of a first (11) of the magnetic regions (11, 12, 13) is different to the maximum strength detectable by the sensor (20) of a second magnetic field of a second (12) of the magnetic regions (11, 12, 13). By determining the time between detected peaks of the magnetic field strength it is possible to determine a rotational speed. Disclosed is also a device for use in determining a rotational direction, in which at least three regions having different characteristics that can be identified by a sensor are provided. The regions can have different magnetic characteristics like magnetic field strength or field direction, they could have different visual characteristics like colour or tone, or different dimensional characteristics like radius or thickness.
The direction can then be determined by the order of the characteristics, e.g. high - medium - low or low - medium - high. The sensor may comprise an optical element mechanically connected to a magnetostrictive element which changes shape or dimension in response to variations of the magnetic field. |
