A Method for Measuring a Short-Range Linear Displacement Using a Magnetic Dipole and Hall-Effect Devices
Tokuji Okada, Hiroshi Tsutsui, Takahiro SAYAMA · Transactions of the Society of Instrument and Control Engineers · 1992
This paper proposes a method for measuring a short-range linear displacement of an object using a magnetic dipole and Hall-Effect devices.To determine a target of the object, a circular plain permanent magnetic dipole is installed on the surface of the object.In the direction of the magnetic field which is vertical to the object's surface, three Hall-Effect devices are placed so that the magnetic flux density is sensed.Supposing the points where magnitudes of the flux density of the magnet are equal exist on a surface of an ellipsoid, the position of the magnet is determined as a cross point of the three elliptical surfaces.Experimental results show the measurement error is within 0.03mm in a box of 1.6×1.6×2mm3volume.Also, a mathematical form for expressing the area of equal magnetic flux is derived and depicted by the use of a computer.Measurement range of the displacement is clarified under such condition that the surface of the area in which the output of the Hall-Effect device is equal is approximated by the surface of a spheroid.The error caused by using the approximated surface is analysed quantitatively.The sensor is useful in measuring the linear displacement from 0.5mm to 2.5mm without the affect of light.