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The origin of the potentiometer
As early as thirty years before this century, potentiometers should have been passed. At that time, it was a potentiometer, which is now a conventional teaching sliding potentiometer ---- sliding line rheostat.
When Galvani and Volt discovered that chemical methods could be used to generate electricity, <1800 AD> they may have difficulty thinking that the parameters in the circuit could be adjusted. By 1827, when the European Union ohm proposed his law of notation, Physicists have made a batch of simple variable-resistance elements. Although his origins are a bit controversial, it is certain that the early variable resistance elements were rarely similar to the existing and widely used by modern engineers. At the end of the nineteenth century, it was only clunky to use this master in the laboratory. And huge instruments.
One type of variable resistance element is a carbon stack varistor. Each carbon sheet is about two inches square and a quarter thick. These carbon blocks are installed in an insulating bracket. Metal blocks placed anywhere in the middle of the carbon stack can be connected For external terminals, the micro adjustment of the resistance value is achieved by the tightening of the bolts to change the mechanical pressure on the carbon pile. One end of the insulating bracket through which the adjusting bolt passes is pressed onto the metal block at the end of the carbon pile. When the pressure increases, the carbon pile is compressed, and the contact resistance between two adjacent carbon blocks is small. Therefore, the total resistance value between the two ends is reduced, and the resistance value is greatly changed. This can be achieved by reducing the carbon block and replacing it with a conductive metal block. It is also possible to place some bands between the two ends of the carbon pile. Reduced terminal blocks to achieve tap and divider effects.
Later, in 1929, the slip mode was developed. This mode has improved a lot on the previous mode. For example, it increases the dissipated power, has a wider adjustment range, and the resistance is high when the carbon block relaxes. The value is very stable.