Temperature compensated hall effect position sensor

Abstract

A temperature compensated position sensor which may be used with hydraulic and pneumatic actuators having a magnetic piston and a non-magnetic cylinder is disclosed. The position sensor comprises a pair of Hall effect sensors mounted adjacent a permanent magnet on the outside of a hydraulic cylinder. One Hall effect sensor is oriented upside down with respect to the second Hall effect sensor such that the two Hall effects sensors perceive equal and opposite magnetic fields. The voltage outputs of both Hall effect sensors are amplified, and one is inverted. The resultant voltage signals are added together. Because changes in temperature produce equal changes in the output voltage of each sensor, the summing process cancels out temperature induced variations in the voltage signals. The resultant sum is dependent only on the magnitude of the magnetic field perceived by the Hall effect sensors, regardless of the variation in temperature. As the piston approaches the position sensor, the magnetic field at the Hall effect sensors rises due to the magnetic piston material forming a flux path between the magnet and the Hall effect sensors. The arrival of the piston at the piston sensor location can therefore be accurately determined from the summed output of the two Hall effect sensors. In one embodiment of the invention, the permanent magnet and Hall effect sensors are contained in a sensor package easily clamped to cylinders of substantially any size.