GB693950A - Improvements in or relating to engine indicators - Google Patents

Abstract

693,950. Engine indicators. STANDARD TELEPHONES & CABLES, Ltd. Aug. 15, 1951, No. 19243/51. Class 106 (ii). In order to improve the display on an engine indicator employing a cathode-ray tube having a time base synchronized from a moving or reciprocating part of the engine under test, one or other of the two synchronizing pulses generated by the timing device is supressed. An engine indicator for use with a reciprocating machine having two similar strokes to each cycle of operation comprises, electronic selecting means for selecting a pulse or train of pulses derived from either the first or the second of the two strokes, a time base which controls the horizontal co-ordinate of an indicator diagram on a cathode-ray tube means for synchronizing the time base, and means for applying the selected pulse or train of pulses to the synchronizing means. A well-known form of Eccles-Jordan " flip-flop " or multi-vibrator circuit is employed in which the anode of each element of a pair of.triodes is coupled to the grid of the other element via an anode-tocathode potentiometer. Thus the grid of V<SP>2</SP>a is coupled to the anode of V<SP>2</SP>b (Fig. 1) via the upper portion R<SP>1</SP> of the potentiometer R<SP>1</SP>, R<SP>2</SP>, while R<SP>3</SP>, R<SP>4</SP> constitute the potentiometer for the V<SP>2</SP>b grid-V<SP>2</SP>a anode cross-connection. In the latter case R<SP>3</SP> is taken to the anode of V<SP>2</SP>a via contacts of a rotary switch S<SP>1</SP>a. The two triode elements of V<SP>2</SP> share a common cathode resistor R<SP>5</SP> decoupled by a capacitor C<SP>1</SP>, and anode voltage is fed from a 400 volt line via the resistor networks R<SP>6</SP>-R<SP>9</SP>. Negative-going pulses from V<SP>1</SP>, which acts as an amplifier and limiter, are passed via the coupling capacitor C<SP>2</SP> and germanium rectifiers X<SP>1</SP> and X<SP>2</SP> in parallel to the two halves of the double triode valve V<SP>2</SP> and reach the grids of the opposite halves via R' and C<SP>3</SP>, R<SP>9</SP> and C<SP>4</SP> respectively. These combinations determine the timeconstant of the multi-vibrator, and, the capacitors C<SP>3</SP> and C<SP>4</SP> being larger than usual, the change-over from one stable state to the other is slowed up accordingly. By means of a selecting switch S<SP>1</SP>a, S<SP>1</SP>b, S<SP>1</SP>c the time base of a cathode-ray tube indicator V<SP>3</SP>, Fig. 1A, may be triggered by either of the two half-cycles of the multi-vibrator so that the engine indicator diagram may be started at the beginning of the engine cycle or half-way through it. Alternative positions of the selecting-switch also provide for the time base being triggered by both similar strokes of the four-stroke cycle in the normal manner. The pulse amplifier V<SP>1</SP> is also arranged to act as a limiter by restricting the screen voltage to a low value so as to limit the amplitude of the negative-going output pulse to about 50 volts at the divider input, this ensures that bouncing contacts mounted on the engine shaft in the pulse source PS do not trigger the time base at the wrong time, this effect is enhanced by giving a long time-constant to the multivibrator couplings to provide an appreciable dead-time period during which the divider cannot be triggered a second time. The pulse source may comprise contacts operated by a cam on the main shaft, or a magnetic pick-up coil co-operating with a magnetic cam on the shaft or co-operating contacts on a reciprocating part of the engine. A manually-operated key for checking the equipment is provided whereby a pulse, the equivalent of a single stroke from the pulse source may be generated.