| 摘要 |
In connection with an optical indication and function monitoring unit for vacuum cleaners comprising optical dust detection means in the form of a luminous diode and a phototransistor provided adjacent the suction duct, and optical indication means for the user, it is proposed to provide, in addition to first delay means for the dust detection means, second delay means having a longer time constant and designed in such a manner that a third flashing luminous diode, which also lights up when the supply battery is nearly run down, is triggered when the dust indication does not operate for an extended period. Further, the pressure switch connecting the unit with the supply battery and responding to a vacuum condition generated by the associated vacuum cleaner is adjusted in such a manner that the whole unit is repeatedly connected to the supply battery when a sufficiently high dust level is reached in the dust bag of the vacuum cleaner so that at least one of the luminous diodes provided for the indication seems to flash.
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