Patent GB-1285028-A (GB)
Title: Improvements relating to determination or monitoring of the distances of surfaces from reference positions
Inventor: MANSFIELD JOHN WILLIAM RYAN
IPC: G01F23/292
Filed: 1968-09-25
Abstract: 1285028 Measuring the distance of a surface from a reference position FLEET ELECTRONICS Ltd 25 Sept 1969 [25 Sept 1968] 45594/68 Heading G1A [Also in Division G4] Apparatus for monitoring the distance of a surface from a reference position comprising a light source providing a light beam and a photo-electric detector having a viewing axis, the light beam being directed at the surface to form a spot of light and either the beam or the viewing axis is moved so that, at least periodically, the viewing axis of the detector passes through the spot and is detected at a point in the movement that varies according to the distance of the surface from said reference position. In an embodiment, Fig.2, the surface 11 of the contents of a package 12 is scanned by a light beam 32 produced from a fixed lamp 28 and reflected by prisms or mirrors 22, 24, mounted on a transparent disc 26 which is rotated by a synchronous electric motor 25. Two photo-cells 17, 17a observe the surface and detect the beginning and ending of the passage of the scanning beam over the surface between the points 19 and 20. The distance between the points 19 and 20 is directly proportional to the distance of the surface 11 below the photocells 17, 17a, Two sets of indicia 27 on the disc 26 are read by stationary lamp 33 and photo-cell 34. The photo-cell 34 is contained in a hollow housing with a slit aperture parallel to the indicia lines, thus as they pass between the lamp and the photo-cell a train of equally timed pulses are produced. The time pulses are fed via an amplifier and a shaping circuit into an AND gate together with the output of a bi-stable circuit which is set and reset by the output from photo-cells 17, 17a. The outputs from the AND gate are fed to a digital to analogue converted to give a measurement of the depth of the package contents 11. A similar embodiment is described, Fig.1 (not shown) in which the scanning beam is generated by a rotary drum assembly (13) surrounding the light source and having lenses attached over apertures in the drum; the axis of rotation of the drum being perpendicular to the plane containing the photo-cell axes. A further embodiment, Fig.4, for measuring the level of the contents of a deep tank comprises a light source 45 projecting a narrow beam 46 vertically downward on to the surface 47 of the tank contents. A photo-cell 48 is moved angularly in the plane of the light beam 46 and its viewing axis 49, whereby the point of intersection travels down the light beam until it passes through the spot 50, at this instance the photo-cell gives a signal. A direct linear read-out is obtained by having a servo motor 52 and lead screw 53 driving a slider 51 along an accurately ground surface 54 which maintains point contact at one corner with a second surface 56 that moves in unison with the photo-cell 48; the geometry of the arrangement being such that a direct digital read-out can be picked off from the slider 51. The arrangement described can be adapted to monitor the thickness of a continuously produced web or band of material from a signal representing a measure of the actual level or depth.