History of the Oscilloscope: Oersted’s Laws and Hand Drawn Waveforms

Learn about the history of the electromechanical galvanometer and the first recorded waveforms.

Found in nearly every any workshop or lab where electrons are being used, many may take for granted all that transpired to bring the oscilloscope into existence. The journey is interesting, and took the culmination of many accidental discoveries and strange observations. 

Here is the second part in a series of the history of the oscilloscope, covering how the link between magnetism and electricity lead to the electromechanical galvanometer, and the first recorded waveforms.

Check out the first part, the early history of the oscilloscope, to catch up or jump ahead to part three, the CRT and modern oscilloscope.

The Link Between Magnetism and Electricity

In part 1, we learned that frog legs could be used to detect the creation and breaking of an electrical current, allowing new insights into electrical systems. However, this was still a far cry from the ability to fully capture a waveform and was only the most rudimentary form of electrical measurements. 

The next step towards the eventual invention of the oscilloscope is the hand-drawn oscillogram. But, before this, the electromechanical galvanometer had to make its debut. This was possible once Hans Christian Ørsted, a Danish physicist, described the relationship between electricity and magnetism in 1820.

Ørsted made this discovery after noticing that a compass needle moved when placed next to a wire carrying a current. André-Marie Ampére, a French physicist, would then come up with the mathematical model of this relationship. This is an essential feature of the galvanometer, which can provide a current measurement based on the current running through a coil with a known electromagnetic constant. 

 

The right-hand rule does a good job of explaining Oersted's observations. Image courtesy of Khan Academy.

 

Electromechanical galvanometers would be essential for the development of telecommunication systems including the Transatlantic telegraph cables which connected North America to Europe, and the first observations of electrical measurements from the brain and heart.

Oscillograms: Manual Waveform Generation

With the galvanometer, it was possible to hand draw electrical waveforms by taking measurements of current around a rotor using a contact, the angle relative to the rotor’s axis, and plotting the current or voltage measurement. Initially, both the rotation of the contact and the plotting of the values were both done by hand, which was not only time-consuming and tedious but fairly imprecise.

French scientist, Jules François Joubert, would develop a method that automated the contact rotation which eased the workload of waveform imaging but still remained imprecise. 

 

Joubert's automated system. Image from the public domain, first appearing in Hawkins Electrical Guide, Volume 6, 1917.

Electromechanical Oscillographs: Automating Waveform Generation

The first fully automated waveform generator was invented by Édouard Hospitalier, French engineer, in 1902. Known as the Hospitalier Ondograph, the device recorded a waveform by moving a pen across a drum of paper, in reaction to measurements from a galvanometer. The charge being recorded would be fed to a capacitor, which would discharge to the galvanometer. Over many successive measurements, an average would be taken to create the overall waveform.

 

The Hospitalier Ondograph. Image from the public domain, first appearing in Hawkins Electrical Guide, Volume 6, 1917.

 

This was still far from being anywhere close to a real-time measurement of a waveform, but improved the ability to gather this data significantly. The Hospitalier Ondograph was also limited by its mechanical components which could only effectively respond up to certain frequencies. 

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As a summary, the mathematical modeling of the link between magnetism and electricity lead the way to the electromechanical galvanometer, providing a more accurate method of measuring current. This then paved the way to the first recorded waveforms, drawn by hand through tedious measurements. Anything that can be automated eventually is, and in the 1900s the first automatic waveform generator is invented which uses a pen on a paper drum to record waveform measurements. 

In part 3, we’ll cover how the invention of the cathode ray tube improved waveform generation, the progression to the modern oscilloscope, and touch on more recent oscilloscope developments.