A very linear noncontact displacement measurement with a hall-element magnetic sensor

Two very linear methods for noncontact position measurement are described. They are based on a relative movement between a Hall-element magnetic sensor and a constant gradient static magnetic field. One method depends on measuring the radial component of the field along a bar magnet at a definite distance from the axis of symmetry. The linearity achieved is approximately 0.1 percent over 75 percent of the magnet length. In the second method, the sensor measures the axial field between two opposing axially magnetized discs. In both methods the output signal is symmetrically opposite with respect to the travel midpoint.