Abstract: A rotary speed sensor system uses a permanent magnet and a Hall cell sensitive to the changing tangential component of magnetic field caused by the interrupted surface profile of a rotary element. In order to avoid anomalies caused by the variation of the base value of the tangential component of magnetic field, the output of a differential amplifier fed by the Hall cell is connected to a voltage averaging circuit which stores the average voltage of the output on a single capacitor. The output of the differential amplifier and the voltage across the capacitor are respectively coupled to the differential inputs of a Schmitt trigger exhibiting hysteresis. The Schmitt trigger thereby establishes operate and release points relative to the average voltage signal. The voltage averaging circuit is a non-linear circuit in which the voltage across the capacitor is fed back to the negative input of an operational amplifier.

Abstract: Device for sensing angular position of a shaft utilizes a flat on the shaft, a permanent magnet with its polar axis perpendicular to the shaft axis, and a magneto-resistive element between the magnet and the flat. The resistance of the element varies linearly as the shaft is rotated from a first position to a second position.