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A high speed oscillograph, using ordinary ink and paper, has been developed that provides a new approach to the old problem of producing instantly visible, high frequency records with inexpensive writing materials. A high speed jet of ordinary fountain-pen ink is divided into a uniform procession of drops, each of which is independently charged in proportion to an input-signal voltage. After projection through a constant transverse-deflecting field, the charged drops are collected on a moving chart to form an instantly visible, permanent record of the input signal. Drops are typically formed at a rate of 100 000/sec; each has an independent trajectory and makes an individual mark representing an independent sample of the input waveform. The ink stream may be switched on or off at high speed by providing, between the drop-launching point and the record surface, a collector that intercepts drops having a specific trajectory. Besides oscillography, which is discussed in detail, the technique has applications in other fields requiring marking at high speed or marking without pressure or physical contact.
Richard G. Sweet (Mon,) studied this question.