Patent GB-1128753-A (GB)
Title: Improvements in or relating to indicator systems
Inventor: GREEN MARTIN RICHARD
IPC: G01R13/28
Filed: 1966-03-07
Abstract: 1,128,753. Cathode-ray tube indicators. MINISTER OF TECHNOLOGY. 7 March, 1967 [7 March, 1966], No. 9891/66. Heading H4T. In a cathode-ray tube indicator system the value of an analogue voltage is indicated by the angular position of a radial trace which is produced by the collapse of a circular scanning field when the analogue voltage is employed to inhibit, temporarily and at a time in the scan cycle determined by its magnitude, the application of the deflection signal to the tube. The beam is normally blanked and a bright-up pulse is applied to the tube simultaneously with and for the duration of the inhibition of the scanning signals. When two or more analogue voltages are to be displayed the duration of inhibition (and of the bright-up pulse) is different for each voltage so that the latter may be distinguished by traces of different lengths. Fig. 1 (Prov.) shows the general scheme in which phase shifters 1, 2, supply the +45 degree and - 45 degree phases of a reference signal to the orthogonal deflection means (plates or coils) of the display tube 4 via inhibit circuits 3, the reference signal also controlling the production of pulses in generator 5 which are width-modulated in 6 by the analogue signal and employed to produce in generator 7 pulses controlling the inhibit circuits and beams brightening pulses. In a modification of this arrangement (Fig. 2, Prov.) the reference pulse generator 5 is controlled by the same 400 c/s. signal from which the deflection waveforms are derived by squaring the 400 c/s. signal at 14 and then dividing-by-four in bistable circuits 15, 16. A further bi-stable circuit 17 supplies pulses which operate switches 19, 22, alternately, to supply to a combining circuit 20 the analogue signal (channel 1) and the latter signal plus its first derivative (channel 2). The combining circuit thus controls the pulse width modulator 6 which produces pulses the trailing edges of respective ones of which are determined by the magnitude of the output of the switches 19, 22 alternately operative. These trailing edges determine the leading edges of inhibit pulses produced in generator 7 and the latter is controlled via a switch 12 by means of a reference voltage and the switching signal supplied to switch 19 such that when switch 19 is closed the length of the inhibit pulse is greater than when switch 22 is closed. Thus the trace indicative of the channel 1 information is longer than that appertaining to channel 2 and where the analogue signal is derived from an aircraft altimeter the angular position of the channel 1 trace indicates the height of the aircraft whilst the channel 2 trace, which is produced by a voltage indicative of height plus a voltage indicative of the rate of change of height indicates the latter (i.e. rate of change of height) by its angular relationship to the channel 1 trace. The absolute angular position of the channel 2 trace then indicates the probable height a short time ahead. In a further embodiment (Fig. 5) the inputs from the two channels are supplied to comparators 28, 29 fed with a ramp staircase waveform from generator 27 to provide outputs to respective ones of monostable circuits 30, 31, the former one 30 of which has a longer period than circuit 31 so that the trace indicative of channel 1 information is longer than that indicative of channel 2 information. The inhibit circuits 3 (described with reference to the circuit of Fig. 4, Prov., not shown) include R.C. time-constant circuits which cause the scanning fields to decay exponentially when inhibited so that a usable trace is produced. The display of the present invention may be produced in one corner of a large screen tube on the remainder of which other information may be displayed either in time-division multiplex or by means of a second electron beam.