Patent GB-639259-A (GB)
Title: Improvements in or relating to devices for measurement of time intervals
IPC: G04F13/02
Filed: 1947-05-08
Abstract: 639,259. Clocks. RAYTHEON MANUFACTURING CO. May 8, 1947, No. 12469. Convention date, Feb. 27, 1943. [Class 139] [Also in Groups XIX and XXXVIII] In a sound-ranging system, the indicator comprises a lamp, which flashes on the receipt of an echo signal, mounted axially within a pair of co-axial cylinders rotating in opposite directions at different angular velocities, the cylinders being opaque except for light transmitting spiral slits formed upon their surfaces. The relative angular velocities of the spirals are so arranged that the locus of the points of intersection of the spirals is a straight line which is situated immediately behind a linear window in the housing surrounding the cylinders, so that when the lamp flashes a spot of light is seen through the window, the position of the spot depending upon the extent of the rotation of the cylinders. In the embodiment described, two sets of spirals are provided, one set co-operating with the window 54. Fig. 2 to provide a coarse range-scale and the other set cooperating with the window 52 to provide a fine-reading scale. The outer cylinder, Fig. 7, has two spiral slits one 62 having one convolution and the other 63 having five convolutions. The inner cylinder, Fig. 5, which has an angular velocity 1.2 times that of the outer cylinder, has one spiral 77 having six convolutions and five spirals, of which one 70 is shown, equally spaced around the cylinder and having 1.2 convolutions each. The positions of the windows 52 and 54 are indicated in Fig. 7, by the points A, A<SP>1</SP> and B, B<SP>1</SP> respectively and in Fig. 5 by C, C<SP>1</SP> and D, D<SP>1</SP> respectively. An exploring pulse is transmitted when the cylinders are in the positions relative to the windows indicated in Figs. 5 and 7. After a complete revolution of the outer cylinder, the point of intersection of the spirals 62 and 70 will have travelled down the window 52 and any echo signal received will have caused a spot of light to be produced at a distance from the point A (or C) proportional to the range of the echo producing object. In the same time the intersection of the spirals 63 and 77 will have moved one-fifth of the way down the window 54 and any echo signal received will have produced a corresponding indication visible through that window. Since during the revolution of the outer cylinder the inner one will have made 1.2 revolutions, during the next revolution the spiral 62 will co-operate with the spiral displaced one-fifth of a revolution from the spiral 70. Thus in five revolutions of the outer cylinder the intersection of one set of spirals will have moved down window 52 five times and the intersection of the other set will have moved down 54 once. It will thus be seen that if the transmitter is keyed when the intersection moving down 54 commences its sweep the distance of an echo-producing object will be indieated by the spot of light seen through the window 54, while the corresponding spot of light seen through the window will enable its range to be determined accurately once the approximate range is known. In an alternative arrangement, the slits are arranged to be in the form of logarithmic spirals which enables more accurate measurements to be made for short ranges than for long ranges.