| 摘要 |
PURPOSE: To perform proper power control of a blower by amplifying the output from a magnetic sensing element installed opposing to a magnet of a valve element using two steps of differential amplifiers, and changing over the signal due to a variable resistor into the amplified signal of the magnetic sensing element and vice versa. CONSTITUTION: The valve element 40 having a magnet 41 fitted to it is installed in an air flow path in a motor-drive blower 53, and a magnetic sensing element 42 is installed opposing to the magnetic 41. When the valve body 40 is shut and the distance between the magnet 41 and sensor elements 42 becomes the shortest, the output of the sensor element 42 maximizes, and the potential difference between the point A and reference point D becomes maximum owing to differential amplification of the first stage amplifier 12. If at this time, a variable resistor 15 is adjusted to make the potential at the point B equal to the point A, the input to the next stage amplifier 21 becomes equal, so that the output X1 becomes equal to the potential at the reference point Y1, and the power of the blower 53 decided by a difference sensing circuit 50 and a phase control circuit 51 becomes maximum. In case, for example a carpet, etc., is to be cleaned, therefore, a strong power of blower 53 can be available when an at-hand switch 31 is changed over by a switcher 45 to turn on the power nozzle. |
