Basic Principles in the Design of Cathode Ray Oscillograph Engine Indicators

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Abstract
Increases in the speed and rating of internal combustion engines have necessitated the replacement of conventional engine indicators by the recently evolved cathode ray oscillograph engine indicator. The devices for converting mechanical pressure into an electrical effect fall into three classes according to whether (1) an electrostatic, (2) a resistance, or (3) an electromagnetic effect is used. Only the first and last classes have been found practicable, the first for rapidly varying and transient effects, and the last for slower phenomena. The members of each class can be used with one of three types of electrical energizing circuits: (1) self-excitation, (2) direct-current excitation, or (3) alternating-current excitation. Success in dealing with a particular problem depends upon the choice of a suitable combination of the device sensitive to pressure, and the electrical energizing circuit. The three most useful combinations are the piezo-electric crystal, and the moving iron, or magnetophone, with either direct-current, or high-frequency alternating-current excitation. Magnetostriction and the condenser microphone, both with either direct- or alternating-current excitation, will prove useful when developed further. The essential features of design for the study of the most difficult problems are now understood. The present form of these engine indicators is useful, but there is need for greater accuracy and reliability.

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