Patent GB-637083-A (GB)
Title: Improvements in or relating to display arrangements for electric oscillographs
IPC: G01S1/02
Filed: 1946-05-14
Abstract: 637,083. Cathode ray oscillographs variable - contact resistances. STANDARD TELEPHONES & CABLES, Ltd., and CLEAVER, R. F. May 14, 1946, No. 14562. [Class 37] [Also in Group XL (c)] Relates to systems for measuring angular quantities by means of a cathoderay oscillograph. According to the invention the system comprises means for deflecting the cathode beam in accordance with the unknown angular magnitude, a device having a rotatable member and adapted to produce a deflection of the beam in accordance with the angular position of the member, switching means for alternately producing on the oscillograph screen indications respectively corresponding to the two deflections, and means for adjusting the member to bring the two indications into registration, whereby the unknown magnitude is determined by the corresponding angular position of the member. The invention is described as applied to a ship-borne directionfinder in which the signals received by two orthogonal directional aerials are applied to the orthogonal deflection systems of a cathoderay tube to produce an indication the angular position of which gives the bearing of the received signal, the bearing being accurately determined by producing a second similar indication by means of a calibrator circuit which is adjusted for coincidence of the two indications. By this means errors due to parallax and to irregularities in the electrode structure of the cathode-ray tube are eliminated and quadrantal instrumental and site errors may be readily compensated. As shown in Fig. 1, in one position of switch 9 the two signals 3 and 2 from the D.F. system 1 are applied to the X and Y plates 5, 6 and 7, 8 of the cathode-ray tube 4 to give a radial trace 65, Fig. 3, as in Specification 590,260, the angular position of the trace being a function of the bearing of the received signal and in the other position of switch 9 the two outputs E1, E2 from a sine-cosine potentiometer 11 of the type disclosed in Specification 602,979 are applied to give a similar trace or electronic cursor 66. The switch 9 is preferably of the electronic type, Fig. 2 (not shown), as disclosed in Specification 637,081, the switching being performed at a rapid rate so that the two traces 65 and 66 appear simultaneously. As shown in Figs. 3 and 4, the potentiometer 11 is enclosed in a box 53 and is provided with a vertical spindle 54 keyed to a horizontal bevel gear wheel 55 which meshes with a vertical bevel gear 56 formed on the back of a rotatable ring member 57 which surrounds the screen 58 of the cathode-ray tube 4 and holds a flat circular glass plate 59 on which is engraved an index mark 63. In operation the potentiometer 11 is adjusted by rotating the ring member 57 until the traces 65 and 66 are coincident and the bearing relative to the ships head as indicated by the index mark 63 is then read off a scale on the fixed annular ring 60 ; a second scale indicating true bearings is provided on the rotatable annular ring 61 which is linked with the ships compass. In an alternative arrangement the two traces 65 and 66 are arranged to be at different distances from the centre so that they may be made coincident without actually overlapping. In setting up the apparatus, the coupling between the potentiometer 11 and the gear wheel 55 is adjusted so that the index 63 reads zero on scale 60 when the angle of the potentiometer is zero and the oscillograph is set with its Y-deflection axis parallel to the fore-and-aft line on scale 60. Any quadrantal error of the oscilloscope due to inequalities between the X- and Y-plate sensitivities is then corrected by setting the index 63 to read port 45 degrees and adjusting the outputs E1 and E2 from the potentiometer 11 by means of the variable. resistors 23, 26. Fig. 1, so that the cursor trace 65 also reads port 45 degrees. A test oscillator is then set up on the test bearing and any usual means for compensating instrumental and site error is adjusted to make the trace 65 coincident with the cursor 66 ; when no such means are provided, the resultant quadrantal error due to all causes may be compensated by adjusting resistors 23 and 26 to make traces 65 and 66 coincident but in this case the direct reading of trace 65 on scale 60 may no longer indicate the correct bearing as in the former method of adjustment. Alternatively quadrantal error may be corrected by making the resistors 23 and 26 equal and deforming the potentiometer square ABCD into a rhombus, and similarly octantal error may be corrected by deforming the square into a re-entrant equilateral octagon as shown in Fig. 5. Specification 590,261 also is referred to.