| 摘要 |
A side wall 51 provided with a coupling hole 50 coupled to the dust transporting pipe 6 of a dust chamber 5 is configured in a sloped shape so as to have a predetermined angle theta with respect to the bottom surface of the dust chamber. A photo detector 14 having a light receiving surface along the surface 51 is disposed near the coupling hole 50 of the side wall 51 . A photo diode 15 for irradiating light toward the photo detector 14 is disposed on the upper surface of the dust chamber 5 . When dust is filled within the dust chamber 5 , since dust is accumulated on the photo detector 14 , the photo detector 14 does not outputs a light detection signal.
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