Design and Realization of a Long-Stroke Displacement Sensor Using Hall Elements

In this work magnetically sensitive electronic components called Hall elements were used to realize a long-stroke displacement sensor (see Fig. 1). Output voltage of Hall elements are induced by magnetic fields, and hence are sensitive to the proximity of ferromagnetic objects like magnets. By creating flux change in the magnetic circuit (see Fig. 2), induced voltage can be read out and used to calculate the actuated displacement.

Fig. 1 Illustration of a displacement sensor         Fig. 2 Possible magnetic flux change design

To achieve the long-stroke objective, three Hall elements were aligned in a linearly cascade manner (see Fig. 3). Characteristic curves of 3 Hall elements are shown in Fig. 4, with the x-axis being the position of the magnet and the y-axis being the readout voltage. Via status of readout voltages, predefined program was able to determine the actuated position of the magnet, and hence the probe displacement.

Fig. 3 Configuration of the proposed displacement sensor (HE stands for Hall Element)

Fig. 4 Readout voltages of 3 Hall elements

First prototype was linked to PC via a data acquisition device, with LabVIEW user interface (see Fig. 5 below). Static performance turned out to be within 1% error with precision up to 2~3 micrometers. And, this prototype was able to respond quickly to measure the vibration of an eccentric motor, which was demonstrated by Fig. 6.

Fig. 5 Measurement system configuration

Fig. 6 Dynamic response capability of the proposed sensor