Roll-over sensor with pendulum mounted magnet

Abstract

A shunt is pivotally mounted to form a pendulum positioned between a reed switch and a magnet. The shunt is formed of ferromagnetic material and is mounted such that as long as it remains between the reed switch and the magnet the reed switch remains open. The shunt is held or biased between the magnet and the reed switch by the force of the magnetic attraction between the shunt and the magnet. The mass of the shunt acts as both a tilt sensor which responds to gravity and an accelerometer sensitive to crash-induced accelerations. The reed switch, magnet and shunt are mounted in a housing which positions the reed switch and magnet and controls the maximum range of motion of the pendulum-mounted shunt. An alternative embodiment employs a subassembly which includes a magnet, a shunt, and a selectively positioned mass, the subassembly is mounted to pivot over a reed switch. The magnet is positioned on or very near the pivot axis. The shunt is positioned further from the pivot axis toward the reed switch. Rotation of the subassembly about the pivot axis results in little displacement of the magnet but a large displacement of the shunt which allows the reed switch to be influenced by the magnet and close. The frequency response and sensitivity of the subassembly can be adjusted by positioning mass about the pivot axis so as to achieve a desired first and second moments about the pivot axis.