6.1 - The instruments genesis
Pocket voltmeter made in the USA circa 1925 for battery voltage measuring used in the early radio receivers
Primitve galvanometer made in France circa 1890
In reality the modern electrical measuring instrument always followed the scientific and technological development. Thus, the Electric- measuring concept started firstly with the researches of the physicist Charles Columb. Columb invented an instrument known as the Columb pendulum that through the same he established the fundamentals laws of the Electricity. Later, the Danish physicist H. C. Oersted, to establish the relation between Electricity and Magnetism used the same laws. The consequences of such experiment were very important to the Electrical science as in 1820 the french scientist André Ampère proved by a series of new experiments that all the magnetic effects mentioned by Oersted could be produced by the electric current alone. He demonstrated the important fact that two parallel wires carrying electric, attract each other when the current flow in like directions, and repel each other when they flow in unlike or opposite directions. He proved that the force of attraction and repulsion is directly proportional to the strength of the currents, and inversely proportional to the square distance between them.
Following Arago invented the first electro-magnet by flowing a current through a wounded wire over a core of soft iron. At this time, in England Faraday was studying the magnetic field produced by different types of circuits.
Around 1823 Ampère built the first measuring instrument known as galvanometer whose term was originated from the name of the famous Italian phycisist Luigi Galvani. In this way, through this instrument now the intensity of the current could be measured accordingly.
If the measurement instruments originated from the evolution of the electromagnetism were so important, certainly the development of the osciloscope was the major contribution of Electronics in the field of measurement of the electrical parameters.
The electron bean generated in the cathode ray tube can be compared to the pointer of the galvanometer used in a classic measurement instrument, but now actuating as an indicator in such away the variations of the measured quantities could be followed in very high speed.
The osciloscope can be used as a recorder also.Nowadays, the modern osciloscope used in several electronic fields is the technological evolution whose roots was the Braun tube invented in1897, several years before the appearance of the first thermionic valve; later known as cathode ray tube. The Braun tube was also the origin of the modern TV screen.