A Gradiometric Magnetic Sensor System for Stray-Field-Immune Rotary Position Sensing in Harsh Environment

Abstract

Contactless magnetic position sensors are used in countless industrial and automotive applications. However, as a consequence of the electrification trend the sensors can be exposed to parasitic magnetic stray fields, and their desired robustness may be compromised. In this paper we publish for the first time how this challenge is addressed and constructively solved using a complete paradigm change leaving conventional magnetic field measurement behind and entering into the realm of magnetic field gradient measurement. Our novel sensor system consists of an integrated Hall sensor realized in 0.18 μm CMOS technology with magnetic concentrators and a four-pole permanent magnet. The intrinsic angular accuracy was assessed comparing the rotary position of the permanent magnet with the sensor output showing angle errors below 0.3°. Additional end-of-line calibration can be applied using built-in memory and processing capability to further increase the accuracy. Finally, we demonstrate the immunity against stray fields of 4000 A/m which led to errors below 0.1°, corresponding to 0.06% of the sensors fullscale angular range. In conclusion, this novel sensor system offers a compact and flexible solution for stray-field immune rotary position measurement in harsh environment.

Experimental Demonstration of Stray-Field Immunity beyond 5 mT for an Automotive-Grade Rotary Position Sensor

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This paper experimentally demonstrates the stray-field robustness capability of a novel Hall-based rotary position sensor concept (Huber, S., et al, 2018). The sensor targets safety-related automotive applications, for example powertrain and power steering.

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“…However, they require more space due to the overhead of the discrete coils. To address the stray-field challenge in Hall-based sensors, we developed a new gradiometric Hall sensor concept described in our companion paper [3].…”

Computationally Efficient Magnetic Position System Calibration

“…The development of MPO systems is an ongoing theoretical and experimental effort dealing mostly with stray field robustness [10], system fabrication tolerances and combining the signals of multiple sensors with sophisticated algorithms [7]. While such complex implementations can achieve a high level of precision and stability, they often neglect the production cost factor, which is a critical aspect for industrial applications.…”

Hybrid Magnetic–Inductive Angular Sensor with 360° Range and Stray-Field Immunity

“…In recent times, due to the increasing electrification of vehicles, stray-field immunity (SFI) has become a key requirement for automotive sensors [ 5 ]. A typical source of stray fields in hybrid or electric cars is the high-current wires, which can produce magnetic fields in the order of several millitesla [ 6 ].…”