| 摘要 |
PURPOSE:To permit correct detection of a speed signal even at a low speed by a method wherein the DC level of the output of an amplifier is detected and is compared with the output signal of the amplifier to output a speed detecting signal whose waveform is shaped. CONSTITUTION:When a multi-pole magnet 2 for detecting the speed is rotated, a speed signal 16 is generated in a speed detecting conductive pattern 1 while the generated speed signal 16 is amplified by an amplifier 17 into a signal having the center at a reference voltage 8 and the DC level of the amplified output of the amplifier 17 is detected by a DC level detecting device 10. The detected DC level is the center value of the output of the amplifier 17 which becomes the reference voltage of a waveform shaper 18. The output of the amplifier 17 is inputted into one input of an operational amplifier 15 while the output of the DC level detecting device 19 is inputted into the other input of the operational amplifier 15 whereby the speed detecting signal, compared and shaped, is outputted. According to this method, a correct rotating speed, immediately before stopping, may be detected upon starting or braking of the motor. |
