A magnetic distance sensor with high precision

Abstract

A magnetic distance sensor working at very low frequency has been developed to measure distances up to 1 m. The principle is similar to that of the 3-D magnetic tracker, but the system is optimized to minimize the error in distance for static measurements. The system is not affected by conductive objects. The uncertainty caused by noise and interference is below 2 mm, even in a noisy environment. The measurement time of 3 minutes can be decreased to 1 minute, depending on the amplitude of the interferences and the required accuracy. After applying corrections, systematic error of 5 mm was achieved by using a calibration model. The system is scalable up to 20 m range.

Calibration of the 3-D Coil System's Orthogonality

“…The arrangement was also presented in [1] where we observed the different calculated results during a rotation test procedure. During this test the distance between the source coil and the sensing head was kept constant, the coil system was rotated along the axis of one coil at the interval of 0 to 360 degrees and the distance was calculated in each 22.5 degrees.…”

“…3, the position offset of the X axis was in our case was corrected with the value of 30 or 20 mm respective. An excitation sequence is similar to the one published in [1]. Current square wave pulses of both polarities are sequentially sent to individual source coils U, V and W. In this way, we can easily remove the Earth's magnetic field vector and, by averaging from several cycles, we can also reduce the noise.…”

Inductive Position and Speed Sensors

“…While such precision would be inacceptable for industrial applications, it is sufficient for medical research. A precise distance sensor based on the principle of magnetic tracking is described in [23]. The system consists of a tri-axial stationary excitation coil system and a moving Billingsley tri-axial fluxgate magnetometer with 0.1 nT field resolution and linearity error below ±0.015% of the full scale.…”

Research of Measurement of Large Displacement and Velocity Based on Hall

“…The Hall components detect the rotation angle and the direction of roll wheel, and then the displacement is calculated. When the magnetic sensing surfaces Hall switch feel a rising magnetic field, and the magnetic flux density is greater than B HL, Hall switch is turned on, and the output is low [12]; When the feel is a decline in the magnetic field and the magnetic flux density is less than B LH, the Hall switch off, and the output is high. The difference Magnetic induction between BH-L and B LH is produced by the magnetic hysteretic effects, which greatly improved anti-jamming performance of the switch circuit.…”