Adaptive Thermo-Compensation of Magneto-Resistive Sensor

摘要

Anisotropic Magnetoresistance occurs in certain ferrous materials and can be applied as a thin strip to become a resistive element. Permalloy is used to form four resistive elements to become a wheatstone bridge sensor. Each magneto-resistive strip element possesses an ability to change resistance in relationship where (θ) is the angle between the magnetic moment (M) vector and the current flow(I) (Fig. 1) [1]. To create the sensor from the AMR elements, the four elements are oriented in a diamond shape with the ends connected together by metallization to form the wheatstone bridge [1, 2]. It should be noted that some errors should be adjusted to enhance the accuracies of the measurements. The first one is the offset error voltage. To compensate for the offset, either analog signal processing or digital value corrections can be used. Another common error to be accounted for is the drift in the material constant versus temperature. This error effects both the bridges sensitivity and offset. Coefficients of temperature (tempcos) of the sensitivity and offset are nominally -0.32%/℃ and -0.01%/℃ respectively [1, 2]. In real systems heating or cooling effects on sensor bridge offset are detected and must be corrected. Fig. 2 shows the typical scenario, the AMR sensor is installed outdoor and is affected by the Earth magnetic field only. If application should have a large operating temperature range (case of outdoor installation -30 +70℃ or more), thermo-compensation technique should be implemented to the application. Francesco Battini and others [3] propose to use preliminary calibration and temperature compensation.