Patent GB-1137475-A (GB)
Title: Improvements in or relating to radiation responsive devices
Inventor: JOHNSTON JAMES STEWART
IPC: G06K11/00
Filed: 1966-01-13
Abstract: 1,137,475. Photo-electric measuring systems. ROSEMOUNT ENG. CO. Ltd. 11 Jan., 1967 [13 Jan., 1966], No. 1730/66. Heading G4H. [Also in Divisions C4 and H1] A fibre which fluoresces when a source of exciting radiation is directed on to it is masked over part of its length so that the position of the source of radiation may be found, a photocell determining when the radiation is falling on the fibre. In one embodiment (Fig. 1) a fibre 10 connected to a photo-cell 11 has a mask (Fig. 2, not shown) movably positioned in front of the fibre so that as the mask is moved a series of output pulses are obtained from the photo-cell 11 representing in binary code the position of a light beam 13. In a second embodiment (Fig. 3) for digitizing the position of a light beam from, for example, the mirror of a mirror galvanometer a plurality of fibres 24, 25; 26, 27; 28, 29; connected to photo-cells 23 are positioned behind a mask 30 so that the light from the mirror 20 falls on to some of the fibres, the parallel output from the photo-cells representing in binary or Gray's binary code the position of the beam. Instead of the apertured mask, the fibres may be wound round opaque support members (Figs. 4, 5, not shown). In the embodiment of Fig. 6, fibres are wound helically around cylindrically arranged support members 51, the first fibre around every other support member, the second around every second support member &c. The rotation of a lead screw on which a mirror 52 is positioned at an angle of 45 degrees to the axis can then be measured by directing a beam of light axially on to the mirror and causing some of the fibres to fluoresce. In two other embodiments (Figs. 8 and 9, not shown) for measuring the angle of rotation of a shaft carrying a mirror, fibres are wound circumferentially and helically respectively round the outside of a cylindrical mask. In an embodiment for determining the level of a liquid 60 (Fig. 7), a float 61 containing an alpha particle radiation source causes selected ones of the fibres 64, 65 behind a cylindrical coded mask 63 to fluoresce so that the output from photo-cells 66 gives a digital indication of the liquid level. To determine the y co-ordinate of an analogue trace (90, Fig. 10, not shown) on an opaque background (91), a plurality of fibres (92) are positioned behind the opaque member (91) so that light from a source (94) shines through the trace (90) to cause selected ones of the fibres to fluoresce so that the output from photo-cells (93) is an indication of the amplitude of the analogue function represented by the trace. The position of the edge of a movable opaque member (100, Fig. 11, not shown) movable in front of a plurality of fibres (101- 104) is found by mechanically or electromechanically moving the ends of the fibres so that each photo-cell (113) gives alternately outputs from two adjacent fibres. The difference in output from any pair of adjacent fibres is thus determined. The position of a light beam (118, Fig. 12, not shown) behind a grid of fibres (116) is indicated in decimal form by photo-cells (117) connected to each of the fibres.