Patent GB-661087-A (GB)
Title: Electrical circuit analyzing apparatus
IPC: F02P17/02
Filed: 1947-10-17
Abstract: 661,087. Cathode-ray oscillographs. BENDIX AVIATION CORPORATION. Oct. 17, 1947 [Oct. 17, 1946], No. 27874/47. Class 37. [Also in Group XL (c)] In an electrical testing apparatus having a control circuit comprising a storage condenser 28 the discharge of which is effected in accordance with the operating cycle of an electrical circuit being tested, for example an ignition circuit, there is provided means, such as gasfilled triode 37, resistance 46 and a vacuum pentode 30, for varying the charging rate of the condenser 28 in accordance with the frequency of current reversals in the circuit under test; the charging rate varying means may also include a second condenser 42. The testing apparatus may comprise an oscillograph 23 connected to an electrical circuit in order to produce indications representing voltage variations in the circuit and the time base of which is synchronized with an event intermittently recurring in a circuit by the discharge of the storage condenser 28. A lead 18, connected to either the primary or secondary windings 10, 12 of an ignition system magneto, is taken to an amplifier 19 and thence to the Y-plates of the oscillograph. A time-base circuit 24 is connected through another amplifier 25 to the X-plates of the oscillograph, which circuit consists of condenser 28, that has one side connected directly and the other side indirectly through the pentode 30, to a D.C. supply 29. A gas-filled triode 32 is connected across the condenser 28 in order to discharge the latter when the triode 32 is made to conduct. The impulse picked up by a capacity transformer or resistance divider connection 33 from a selected spark plug lead energizes a transformer, the secondary 35 of which is connected across the cathode and grid of the other gas-filled triode 37, and makes the latter conduct. The condenser 42 and the primary 43 of a time-base transformer are connected in series across the anode and cathode of the triode 37, and hence the supply 29, so that the condenser 42 discharges when the triode 37 conducts and ener. gizes transformer primary winding 43. The secondary winding 44 of the latter transformer is now energized and being connected to the grid of the time-base triode 32 causes that valve to conduct. The resistance 46 is placed between the cathode of triode 37 and the supply and because the current through this line is pulsating, due to the periodic conduction of triode 37, the voltage drop across the resistance 46 will be directly proportional to the pulse frequency and therefore to engine speed. This voltage drop is applied to the control grid of the pentode valve 30, the anode of which is connected to the time-base condenser 28, so that the current flow through the pentode to the condenser 28 is proportional to engine speed and the horizontal sweep amplitude of the oscillograph beam remains constant under all conditions of engine operation. In modification, the control of the time-base triode and pentode is effected from different circuits. The pentode grid circuit is taken from lead 18 through a transformer to the grids of two gasfilled triodes which are provided to permit of the use of impulses of opposite polarity, and then to the speed sensitive resistance. The pulses for triggering the time-base triode may' be taken directly from the secondary of the time-base transformer by taking the ignition system pick-up connections directly to the primary of this transformer. Any other type of oscillograph might be used in place of the cathode-ray instrument. Specification 563,502 is referred to.