A dependable AMR sensor system for automotive applications

The increasing replacement of mechanical parts by x-by-wire systems in automotive applications allows improving driver safety. These systems demand highly dependable sensors that ensure their functionality despite the harsh operating conditions. This means that the sensors should be capable of working continuously despite catastrophic faults and keeping the performance over time. An anisotropic magnetoresistance (AMR) sensor is a magnetic sensor commonly used for angle measurements in cars. It is affected by catastrophic faults and performance degradation due to undesired parameters included at the sensor outputs. Until now, physical redundancy is often used to handle catastrophic faults. For the performance, compensation factors for the undesired parameter, such as offset voltage, are estimated at the start of the sensor life. Although the undesired parameters drift due to aging effects, the sensor performance remains within the allowed tolerant band. However, this tolerant band will decrease in the future because the dependability requirements are continuously increasing. Therefore, it is necessary to consider strategies to guarantee the sensor performance over time. This paper proposes a system to improve the sensor dependability using analytical redundancy for catastrophic faults but also with self-x properties to maintain the sensor performance over time. Results indicate a dependability improvement in terms of reliability, with a reduction of 50% in the rate of uncovered failures. The safety requirement ASIL level D is satisfied, and with regard to maintainability, the sensor performance is maintained over time

Online monitoring of the maximum angle error in AMR sensors

Anisotropic Magnetoresistance (AMR) sensors are often used for angle measurements. The sensor outputs consist of two sinusoidal signals that show undesired characteristics as offset voltage, amplitude imbalance and harmonics, which affect the angle measurements. These parameters change due to aging effects, but until now it is considered that these variations do not affect the sensor accuracy. The largest sources of angle error are compensated at the start of the sensor life but they are not monitored during its lifetime. However, the accuracy requirements are increasing and in the future, it will be necessary to verify that the sensor satisfies the accuracy despite aging. This research proposes different equations that are useful to monitor online the maximum angle error due to different sources. Based on this information it is possible to take action in order to guaranty the accuracy during the entire sensor lifetime