Temperature compensated magnetoresistive position sensor

Abstract

A temperature compensated magnetoresistive position sensor is disclosed. The sensor includes two magnetoresistor (MR) elements biased with magnetic flux from a permanent magnet, and connected electrically in series with a precision resistor and a voltage source. A magnetically permeable slide bar is movable to positions within a defined range adjacent to the sensor for varying the magnetic flux and changing the resistance of each MR element, while maintaining the sum of the resistances of the MR elements essentially constant. For a given slide bar position, the voltage drops appearing across the precision resistor and the MR elements are processed by a computer to determine the value for a resistance ratio, where the resistance ratio equals the resistance of one of the MR elements divided by the sum of the resistances of both MR elements at the sensor operating temperature. The determined value for the resistance ratio is transformed based upon the sum of the MR element resistances to obtain a compensated resistance ratio value that would occur for the same slide bar position at room temperature. The compensated resistance ratio value is then used in conjunction with the known behavior of the sensor at room temperature to provide an accurate indication of the slide bar position that is essentially unaffected by the influenced of sensor operating temperature. A correction term can also be added to the compensated resistance ratio value to account for any mechanical offset associated with sensor component tolerances.