Accelerometer with dual-magnet sensing mass

Abstract

An acceleration sensor comprises a tube formed of an electrically-conductive non-magnetic material; a magnetically-permeable element, such as a iron washer, proximate with the passage; and a sensing mass in the passage comprising a pair of permanent magnets and a spacer whose magnetic permeability increases with increasing temperature, with the magnets being secured to the opposite sides of the spacer so as to place a pair of like magnetic poles in opposition. In operation, the sensing mass interacts with the iron washer so as to be magnetically biased to a first position in the passage, while the magnetic-permeability of the spacer and, hence, the magnetic flux generated by the sensing mass adjusts to maintain a nearly constant threshold magnetic bias irrespective of variations in sensor temperature. The sensing mass is displaced in response to acceleration of the housing from its first position in the passage towards a second position therein when such acceleration overcomes the threshold magnetic bias, while the tube itself interacts with the sensing mass to provide magnetic damping therefor. Upon reaching the second position in the tube, the sensing mass electrically bridges a pair of contacts to indicate that a threshold level of acceleration has been achieved. An electrical coil is secured proximate with the iron washer which, when energized, reversibly magnetizes the latter, whereby the sensing mass is either repelled to the second position in the tube or more strongly biased towards the first position therein.