PASSAGE DETECTOR

PURPOSE:To reduce the size while facilitating the mounting/demounting work by fixing the part for coupling a carrying pipe integrally with a tubular body at an end part thereof. CONSTITUTION:A tubular body 2 is provided, at the opposite ends thereof, with coupling parts 10 each comprising a receiving seat 11 formed by tapering the end part of the tubular body 2, a joint metal 12 disposed oppositely thereto, a gasket 13, and a fastening ring 14. Carrying pipes 51A, 51B are inserted, at the end parts thereof, into the openings at the opposite ends of the tubular body 2. The pipes 51A, 51B abut, at the forward ends thereof, on the step parts 5, 5 and positioned in place. Consequently, the optical path ((alpha) of an optical sensor 6 is not blocked by the pipes 51A, 51B. The small diameter part 4 has an inner diameter equal to those of the pipes 51A, 51B and thereby it is made flush therewith. The ring 14 is then fastened thus fixing a passage detector 1 between the pipes 51A, 51B. Since any separate coupler is not required, the size of detector 1 can be reduced, especially in the axial direction.