Absolute angle measurement using the earth-field-referenced hall effect sensors

A miniaturized absolute angle sensor utilizing Hall generators referenced to the Earth's ambient magnetic field has been developed. The sensor has three-dimensional angular sensitivity which allows the output to be self-normalized resulting in high immunity to both B-field and temperature induced errors. The individual Hall generator elements were operated with a final sensitivity of 4.07 V G-1. The Earth's field, magnitude 0.486 G with a surface declination angle of 58.2 degrees (San Diego, California), was used as the excitation/reference field. Bandwidth limiting, low-noise design, and active/passive thermal compensation techniques were employed resulting in a sensor bandwidth of DC to 100 Hz with a maximum signal-to-noise ratio of 44.5 dB. The maximum angular resolution of the sensor was measured to be +/- 0.27 degrees. Temperature induced error was measured to be less than 2% from 25 degrees C to 40 degrees C. The measurement of shoulder joint rotation was used as the test case application for the sensor with excellent agreement between theoretical and experimental performance.