An automatic oscillograph with a memory

The memory oscillograph described in this paper is used for obtaining photographic records of randomly occurring electric transients. This instrument differs from other oscillographs of the memory type
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in that its operation is completely automatic. Forty sets of oscillograms can be recorded without the aid of an operator. Because of this feature, such an oscillograph may be used for monitoring electrical systems in which sporadic circuit disturbances are to be studied. The unit consists essentially of three cathode-ray tubes with associated power supply, a saw-tooth oscillator to provide the horizontal time axis, amplifiers for the vertical deflection circuits, a beam blanking circuit, and an automatic camera. When the memory oscillograph is in operation, the cathode ray tubes are continuously excited. The vertical deflection circuits of the tubes are connected to the voltages to be investigated, and each tube screen carries a cathode-ray pattern characteristic of the voltage applied to its vertical deflection plates. Upon the occurrence of a transient pulse, the camera shutter is released and the electronic beams of the cathode ray tubes are interrupted. The camera then records the persistence of fluorescence, which is characteristic of the material used on the tube screens. In this way a record is obtained of electric events that occurred previous to the opening of the shutter. To insure successful operation, the component parts of the automatic memory oscillograph must be electrically co-ordinated and controlled. The sequence of functions performed by a control circuit for this purpose is described. Photographic records of transients which may arise during the operation of a mercury-arc polyphase inverter are included.