As early as thirty centuries before this century, there should be adjustable resistors. At that time, the adjustable resistance was the conventional teaching slide potentiometer----slide line rheostat.

When Galvani and Volt discovered that chemical methods could be used to generate electricity, they might have difficulty in 1800 AD to adjust the parameters in the circuit. By the time the EU proposed his law of indication in 1827, physics around the world. The scientists made the first simple variable resistance originals. Although his origins are somewhat controversial, it is certain that the early adjustable resistor elements were rarely similar to those currently available and used by modern engineers. At the end of the 19th century, it was only used in the laboratory. Huge instrument.

One of the earliest adjustable resistors is a carbon stack varistor. Each carbon piece is about two inches square and one quarter thick. These carbon blocks are mounted in an insulating bracket, and metal blocks placed anywhere in the middle of the carbon pile are available. When the external terminal is connected, the slight adjustment of the resistance value is achieved by the tightening action of the bolt to change the mechanical pressure applied to the carbon pile. One end of the insulating bracket through which the adjusting bolt passes is pressed against the metal block at the end of the carbon pile. When the pressure is increased, the carbon pile is pressed, and the contact resistance of the two adjacent carbon blocks is small. Therefore, the total resistance between the two ends is reduced, and the resistance value is largely changed. By reducing the carbon block and replacing it with a conductive metal block, some bands can be placed at some intermediate positions between the two terminals of the carbon pile. Reduce the block of the terminal to achieve tap and partial pressure.

Later, in 1929, the adjustable resistor developed into a slip mode. This mode has been improved in the previous mode, such as increasing the power dissipation, having a wide adjustment range, and when the carbon block is relaxed at high resistance. The stability of the resistance value is very good.

Nowadays, adjustable resistors have been booming, and various high-precision potentiometers are constantly being applied to various industries.