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 third and final part in a series of the history of the oscilloscope, describing the evolution of the oscillograph using light, the invention of the cathode ray tube, to the form we are familiar with today.
You can check out the first two parts of this series here:
Visualizing with Light: Photographic and Mirror Waveforms
In part 2, we learned about the progression to automating part of the waveform development process with the Hospitalier Ondograph, invented by French physicist, Édouard Hospitalier. While this invention managed to speed up part of the process, there was still a great deal of labor involved, it still lacked precision, and it was limited by the frequency of the signal. This was also still an indirect measurement of the waveform being measured and was not occurring in real-time.
A step closer to real-time, accurate waveform measurement came with the invention of the moving coil oscillogram. Invented by English engineer William Duddell in the early 1900s, the device worked by rotating a mirror that was suspended in oil and exposed to magnetic fields of the measured current. The mirror would rotate based on the direction and strength of this current, and a beam of light would be reflected onto a photographic slide to record the beam. This made it possible to record signals of higher frequencies.
There was still a barrier to providing real-time measurements, since the photographs had to be developed, but simplified the process significantly.
Invention of the Cathode Ray Tube and Commercial Adoption
The development and subsequent commercialization of the cathode ray tube (CRT) would lead to the first early oscilloscopes. The CRT oscilloscope began as an experimental instrument invented by German physicist, Karl Ferdinand Braun in the late 1800s, and provided insight into the behavior of electrons. Charged deflector plates would deflect electron beams onto a phosphorous coated surface, giving immediate visual insight.
The concept would be further developed and used in commercial equipment in 1932 by A. C. Cossor, a British company that would eventually become Raytheon. The CRT oscilloscope was widely used during World War II, and variations were made using different phosphorescent materials. This material had an impact on the intensity of the visualized signal, and how long it took to fade. Some materials would be more suitable for single trigger or low-frequency waveforms, which would fade more slowly and be visible for longer, for example.
These CRT oscilloscopes were initially not very accurate for measurement, but were great at providing insight into electrical system behaviors.
The A.C. Cossor 1035 MKIII CRT display oscilloscope, released in 1950. Image courtesy of Richard Sears.
Frequency Trigger and Time Trigger
In the 1930s, another company gained significant momentum in oscilloscope development. DuMont began selling the DuMont 164 oscilloscope in 1939, and invented the first frequency trigger and sweep oscilloscope, the Model 224-A.
Shortly after the war, in 1946, Tektronix, Inc. was founded. One of the four founders, Howard Vollum, invented the first time based triggered oscilloscope known as the Tektronix Type 511. Vollum was motivated to develop a device that could provide quantitative measurements. The calibrated, CRT based 511 would weigh 65lbs, consume 180 W, and retail for $795USD in 1947 (equivalent to just under $10,000 in 2019). It had a frequency range of 10 Hz-10 MHz.
Tektronix would continue to innovate in the oscilloscope domain, growing from a company of 12 employees in 1947 to 359 employees in 1952.
Tektronix Type 511 oscilloscope. Image courtesy of W140.
Solid State to Digital
Between the remainder of the 1940s to the 1970s, several other companies would also make traction in the market, including Hewlett-Packard and LeCroy. Hewlett-Packard would introduce the HP 1200A in 1969, the first completely solid-state oscilloscope featuring a bandwidth of 500KHz.
While the invention of the digital oscilloscope can be credited to Tektronix, thanks to engineer Hiro Moriyasu, LeCroy would beat them to the punch by releasing the WD 2000 in 1971, a real-time digital oscilloscope. The WD 2000 had a memory of 20 samples and a sampling rate of 1 ns.
HP would be the first company to sell a fully digital, microprocessor-based oscilloscope: the HP 1980A/B.
HP 1980A. Image courtesy of HP Memory Project.
Oscilloscope Technology Today
It can be hard to keep up with the innovations that continue to occur in the oscilloscope domain today. What is certain is that in the decades between the 1930s and 1980s, oscilloscopes rapidly became more precise, faster, portable, and affordable.
Innovations today range quite significantly, from increased bandwidth, channels, decreased size and power, or even combining multiple tools into one device (such as the case with the MDO300 Tektronix series, which is a 6-in-1 oscilloscope/digital multimeter/spectrum analyzer/logic analyzer/protocol analyzer/arbitrary signal generator). There are even devices like the Pokit meter which pairs with a user’s smartphone to provide oscilloscope function.
Measuring electricity and understanding the phenomenon has been a long journey. Electricity was a poorly understood force, and initial measurements of it were crude. Advancements in several fields had to occur before the oscilloscope was possible: general physics knowledge of electricity, the link between electricity and magnetism, tools to automate measurement collection, and then eventually the CRT.
Thank you for sticking with us on this series! Let us know in the comments below if you're interested in learning more about other historical equipment or engineers.
Featured image used courtesy of Krzysztof Kamil.