DC magnetic field type eddy current speed sensor detecting cross magnetization field with amorphous core

A new dc magnetic field type eddy current speed sensor is presented using an amorphous core of zero-magnetostriction and sharp rectangular B-H loop. In the proposed sensor, a constant dc magnetic flux passes through the surface of a moving conductor of which speed should be detected. So induced eddy currents become a pure function of the speed. The magnetized field produced with the currents, which is called "cross magnetization field" in this paper, is detected with high sensitivity by using such an amorphous core. A "zero flux method" is applied to the detection and it achieves a stable and driftless sensing almost without delay. By making a slight modification, the speed is detectable even if the gap-length between the conductor and the sensor changes. Experimental results are shown.