Remote flow transducer for communication cable

Abstract

A method and apparatus for remotely monitoring air leakage in communication cables is disclosed. Improved volume flow meters are remotely attached at the air inlet to manhole mounted manifolds for supply of dehumidified air to telephone cables. Dehumidified air passes through the remote meters into the manifolds and then interior of a sheath of a communication cable wherein the discrete conduits can be kept dry and under air pressure. The remote volume flow meter at each manifold includes a diaphragm having an air flow conduit mounted in movable opposition to a variable area orifice. The diaphragm actuates a variable resistor, which preferably includes a tailored neutral density wedge. This tailored neutral density wedge moves with the diaphragm towards and away from a position between a light source (typically a light-emitting diode) and a photo sensor (typically of the photo resistor variety). The volume flow meter receives its power through and also has its output communicated through a single pair of wires. Powering of the light source occurs through an alternating current path consisting of a transformer secondary and regulator. Monitoring of the photo sensor output occurs by coupling the photo sensor element in series with the transformer primary and bypassing the alternating current path with a capacitor shunt. As a result, a remotely located meter, when dialed or remotely sampled, can indicate by variable penetration of the neutral density wedge, a changing resistance which is directly related to diaphragm position, and hence flow through the meter. This signal from a remote manhole location can be monitored from a distant central monitoring station, such as a central telephone office. Through a network of such flow meters in combination with conventional pressure transducers, cable air leaks can be detected, rapidly measured as to their suspected severity, and located with improved precision for timely repair.