Patent GB-1189473-A (GB)
Title: Display and Testing Control Apparatus
IPC: G01R13/20
Filed: 1967-06-05
Abstract: 1,189,473. Cathode-ray tube displays; transistor sawtooth circuits. AUTOSCAN Inc. 5 June, 1967 [10 June, 1966], No. 25877/67. Headings H3T and H4T. [Also in Division G1] In a cathode-ray tube display arrangement for analogue signals which recur with variable frequency, specifically the ignition pulses of an internal combustion engine, the pulses are utilized to produce transverse deflection of a linear sweep time-base which is triggered by a portion (the initial spike) of a selected one, or of each one, of the pulses which also control the slope of the sweep (i.e. the time-base speed) as a function of trigger frequency (i.e. as a function of engine speed). Referring to Figs. la and 1b the sweep signal (e), Fig. 2, is produced by charging a capacitor 18 (Fig. 1a) to the potential +B via transistor 17 and when 17 is cut-off allowing 18 to discharge via transistors 19, 20, the rate of discharge is controlled by a potential CCV produced via an integrator 22 in accordance with the potential at point 33 which potential is determined by the flow of current into or out of a circuit 30 supplied from a flip-flop EOSF operating at the trace-retrace rate of the sweep generator. For charging capacitor 18 transistor 17 is rendered conducting by the output of a clock pulse generator CLO (also Fig. 2) in response to either the occurrence of a trigger pulse SCOA (Fig. 2) from a selected spark plug (i.e. via pick-up 12, switch 51d closed and OR gate 23) or a trigger pulse CYN (Fig. 2) from each spark plug (i.e. via pick-up 11, gates 14, switches 51b, 52c and OR gate 23), the clock pulses being fed to transistor 17 via OR gate 16. Transistor 17 may also be rendered conducting via gate 16 by the set output of flip-flop ESOF which is set by a pulse EOS (Fig. 2) whenever the amplitude of the swep voltage across capacitor 18 reaches a level +A (Fig. 2) (ALB) or lower. To prevent spurious operation, e.g. by noise &c. signals, the gates 14 are operated to pass the output of threshold detector 13 (which selects the spike 111(a), Fig. 3, of the CYNA pulses) at the expected time of arrival of the CYNA pulses by controlling them by the output of flip-flop ESOF and the output of a level detector 29 producing a pulse CYNG when the amplitude of the sweep voltage has decreased to a level C, where B>C>A. Thus the sweep voltage has a constant amplitude and a slope that varies directly as a function of the trigger recurrence frequency. Such sweep voltage is then supplied over conductor 24 to the horizontal sweep coil 101 of the display tube 100 (Fig. 16) the Y deflection coil of which is supplied with the pulses CYNA (Fig. 2) derived from pick-up 11. The latter pulses are thus displayed in side-by-side relationship on a single horizontal line. However, provision is made by means of a digital counter 42, having a total count equal to the maximum number of cylinders in the engine, and a selector switch 40, for displaying the ignition pulses of a single selected cylinder alone, appropriate blanking pulses being supplied to the tube control grid. Additionally, by supplying the counter output to a D/A converter 43 a shift signal is produced and combined with the CYNA pulses in adder 49 the output of which, when selected by switch 55, causes each CYNA pulse to be displayed on vertically spaced horizontal lines. In another operational mode all the CYNA pulses may be displayed in an overall superimposed relationship. Since the spikes 111 are very steep and thin a circuit including a differentiator 71 is utilized to increase the beam intensity during the occurrence of such spikes to preserve uniform intensity of the overall trace. In another operational mode switch 52a is opened (other switches also being operated) and the rate of discharge of capacitor 18 is then determined by the rate existing before the operation of switch 52a. The arrangement then operates the tube blanking being suitably controlled to allow display of the portion of the CYNA pulses (denoted by an asterisk in Fig. 2) which occurs prior to the trigger instant (i.e. prior to the occurrence of spike 111). Other facilities provided include means 62 (Fig. 1b) for short circuiting the breaker points of the ignition system to prevent the production of a pulse CYNA in respect of a selected cylinder (thus determining, should there be no decrease in engine speed, that such cylinder is faulty), the engine RPM being determined by a tachometer 90 or by a pointer instrument 80<SP>1</SP> responsive to the peak of the discharge of capacitor 18 supplied over conductor 24. A flashing strobe lamp is provided to permit observation of a timing marker 85 on the fly-wheel with respect to fixed reference marks 86, the flash rate being indicated by means 80<SP>11</SP>, an indicator 89 responds to too-high a voltage across the breaker points when closed and too-low a voltage when they are open and a pointer instrument 80<SP>111</SP> is utilized to provide a measure of the closing time of the breaker points in relation to the ignition cycle for each cylinder.