DC motor rotational speed measurement device - uses coil having several enamelled wire turns round one of fixed magnets positioned around rotor

摘要

The system is for the measurement of the rotational speed of DC motors removing the need for a tachometer or an optical coder. The measurement technique is esp. applicable to small motors used in dental equipment. An electrical output proportional to speed is obtained from a coil (5) having several enamelled wire turns wound around one of the motor fixed magnets (1) positioned around the rotor (3). The rotor has, ideally, regularly spaced rectangular slot widths (a) equal to their spacing (b). The signal output is sinusoidal and may be increased by providing similar coils on the remaining magnets. The technique is equally applicable to two pole motors with brush connections or to brushless DC or interrupted DC multipole motors.