![]() The interior of a cathode-ray tube for use in an oscilloscope. Frequency response was into at least the low audio range. Moving-paper oscillographs using UV-sensitive paper and advanced mirror galvanometers provided multi-channel recordings in the mid-20th century. Įven earlier, audio applied to a diaphragm on the gas feed to a flame made the flame height vary, and a spinning mirror polygon gave an early glimpse of waveforms. A time base, unsynchronized, was provided by a spinning mirror polygon, and a collimated beam of light from an arc lamp projected the waveform onto the lab wall or a screen. In the 1920s, a tiny tilting mirror attached to a diaphragm at the apex of a horn provided good response up to a few kHz, perhaps even 10 kHz. Although the measurements were much more precise than the built-up paper recorders, there was still room for improvement due to having to develop the exposed images before they could be examined. To perform a waveform measurement, a photographic slide would be dropped past a window where the light beam emerges, or a continuous roll of motion picture film would be scrolled across the aperture to record the waveform over time. This reduced the measurement device to a small mirror that could move at high speeds to match the waveform. This was done with the development of the moving-coil oscillograph by William Duddell which in modern times is also referred to as a mirror galvanometer. In order to permit direct measurement of waveforms it was necessary for the recording device to use a very low-mass measurement system that can move with sufficient speed to match the motion of the actual waves being measured. (Such wave-form measurements were still averaged over many hundreds of wave cycles but were more accurate than hand-drawn oscillograms.)įilm recording of sparking across switch contacts, as a high-voltage circuit is disconnected It automatically charged a capacitor from each 100th wave, and discharged the stored energy through a recording galvanometer, with each successive charge of the capacitor being taken from a point a little farther along the wave. The device known as the Hospitalier Ondograph was based on this method of wave form measurement. Due to the relatively high-frequency speed of the waveforms compared to the slow reaction time of the mechanical components, the waveform image was not drawn directly but instead built up over a period of time by combining small pieces of many different waveforms, to create an averaged shape. The first automated oscillographs used a galvanometer to move a pen across a scroll or drum of paper, capturing wave patterns onto a continuously moving scroll. Schematic and perspective view of the Hospitalier Ondograph, which used a pen on a paper drum to record a waveform image built up over time, using a synchronous motor drive mechanism and a permanent magnet galvanometer This process could only produce a very rough waveform approximation since it was formed over a period of several thousand wave cycles, but it was the first step in the science of waveform imaging.Īutomatic paper-drawn oscillograph The contact point could be moved around the rotor following a precise degree indicator scale and the output appearing on a galvanometer, to be hand-graphed by the technician. This consisted of a special single-contact commutator attached to the shaft of a spinning rotor. ![]() This process was first partially automated by Jules François Joubert with his step-by-step method of wave form measurement. By slowly advancing around the rotor, a general standing wave can be drawn on graphing paper by recording the degrees of rotation and the meter strength at each position. The earliest method of creating an image of a waveform was through a laborious and painstaking process of measuring the voltage or current of a spinning rotor at specific points around the axis of the rotor, and noting the measurements taken with a galvanometer. The modern day digital oscilloscope is a consequence of multiple generations of development of the oscillograph, cathode-ray tubes, analog oscilloscopes, and digital electronics. The first recordings of waveforms were with a galvanometer coupled to a mechanical drawing system dating from the second decade of the 19th century. This was important in developing electromagnetic theory. The history of the oscilloscope was fundamental to science because an oscilloscope is a device for viewing waveform oscillations, as of electrical voltage or current, in order to measure frequency and other wave characteristics. ![]() ![]() Illustration of Joubert's step-by-step method of hand-plotting waveform measurements ![]()
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