An instrument for the rapid production of a decimal series of potentials and its application to ballistic measurements

Abstract

An instrument for producing decimal subdivisions of a chosen potential was developed for calibrating a cathode-ray oscillograph, often within a few milliseconds after the ballistic record had been obtained. The maximum potential could be chosen as any integral multiple of 10 millivolts, with a maximum of 100 millivolts. To permit this choice, ten 10-ohm coils were connected in series, and a current of 1 milliampere was sent through them. Then the drop in potential over each coil was 10 millivolts, and the maximum output potential was the product of 10 millivolts and the number of coils included between the output terminals. The decimal subdivisions of the chosen potential were obtained by varying the current in the ten 10-ohm coils in steps of 0.1 milliampere from 0 to 1.0 milliampere by shunt resistances. The calibration started with zero voltage when the shunt resistance was zero, and the shunt resistance increased in such steps that the current in the 10-ohm coils increased in 0.1 miJliampere steps and hence the output voltage in decimal steps of the chosen maximum potential. The shunt resistances were inserted by opening switches that normally short-circuited them. For oscillograph calibration these switches were opened in succession by a falling weight. The numerical data used for illustration are based on decimal subdivision of the maximum available potential. The general case is treated, however, showing that a calibrator of this type may be used for any desired number of potential steps.