André Blondel and the Oscillograph

André Blondel

André Blondel

On August 28, 1863French engineer and physicist André-Eugène Blondel was born. Blondel is the inventor of the electromechanical oscillograph, a device that allowed electrical researchers to observe the intensity of alternating currents, and a system of photometric units of measurement, such as the lumen and other new photometric units for use in photometry, based on the metre and the Violle candle.

André Blondel was employed as an engineer by the Lighthouses and Beacons Service until he retired in 1927 as its general first class inspector.Blondel became professor of electrotechnology at the School of Bridges and Highways and the School of Mines in Paris.

During the early 1890s, André Blondel attempted to solve the problem of integral synchronization, using the theory proposed by Cornu. He managed to determine the conditions under which the curve traced by a high-speed recording instrument would follow as closely as possible the actual variations of the physical phenomenon being studied. This led Blondel to invent the bifilar and soft iron oscillographs.

André Blondel demonstrated these devices at the St. Louis Exposition in 1904 where they won the grand prize. Blondel’s devices turned out to be more powerful than the existing classical stroboscope and remained the best way to record high-speed electrical phenomena for more than 40 years. Later on, they were replaced by the cathode ray oscilloscope. Blondel was able to significantly contribute to the way of better understanding of the behavior of alternating current.

Blondel also built a theory of rectification with asymmetrical electrodes. He demonstrated that there were three kinds of electric arc: the primitive arc of William Duddell, the secondary arc of Valdemar Poulsen, and a succession of oscillatory discharges. He proposed lumen and other new measurement units for use in photometry, based on the metre and the Violle candle.

In 1899, André Blondel published his “Empirical Theory of Synchronous Generators”. In it, he discussed the basic theory of the two armature reactions (direct and transverse). It was used to explain the properties of salient-pole AC machines. About ten years later, he worked on one of the first long distance schemes for the transmission of AC power. Back then a large 300,000 hp hydroelectric power plant at Genissiat on the Rhône was created with André Blondel’s contribution that transmitted electrical power to Paris more than 350 km away using polyphase AC current at 120 kV.

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