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Introduction to the Types and Structural Characteristics of Adjustable Resistors

Time：2023-07-26

　　A variable resistor typically consists of a resistive element and a rotating or sliding mechanism. Its operating principle is broadly similar to that of a potentiometer. When a voltage is applied across the two fixed terminals of the resistive element, adjusting the position of the contact point along the resistive element via the rotating or sliding mechanism allows you to obtain a voltage between the moving contact and the fixed contacts that is directly proportional to the position of the moving contact. However, today there are numerous different specifications and types of variable resistors available. So, do you have any familiarity with these various specifications? If not, below we’ll share an introduction to the different types of variable resistors as well as their structural characteristics.

　　Description of Adjustable Resistor Types:

　　The letter designations preceding conventional general resistors indicate products of different specification types:

　　(1) The letter “C”: solid

　　(2) The letter “S”: oxide film

　　(3) The letter “W”: cement

　　(4) Letter “T”: Special (Fuse)

　　(5) The letters “RJ”: Metal film

　　(6) The letters “RJ”: Metal Oxide Film

　　Analysis of the Structural Characteristics of Adjustable Resistors:

　　1. A variable resistor typically has a slender, cylindrical shape, about 1 cm in length and roughly 0.3 cm in diameter. The size of the resistor varies; the larger its volume, the greater its power rating. For resistors with the same power rating, metal-film variable resistors are smaller in volume than carbon-film variable resistors.

　　2. A variable resistor has only two leads, and these two leads have no distinct positive or negative polarity. Typically, the two leads of a variable resistor extend along the axis of the component body and can be bent for easy installation on a circuit board.

　　3. Nowadays, color-coded adjustable resistors are more commonly used. These resistors have four color bands (though some others have three or five bands). The color bands indicate the resistance value and the tolerance grade of the adjustable resistor. For non-color-coded adjustable resistors, the resistance value and other parameters are directly marked on the resistor itself.

　　On the Working Principle of Adjustable Resistors

　　A variable resistor consists of a resistive element and a rotating or sliding mechanism. Its operating principle is somewhat similar to that of a potentiometer. When a voltage is applied across the two fixed terminals of the resistive element, adjusting the position of the contact point along the resistive element via the rotating or sliding mechanism allows a voltage proportional to the position of the moving contact to be obtained between the moving contact and the fixed terminals. On the exposed resistive element, one or two movable metal contacts are pressed firmly against it. The position of these contacts determines the resistance value between any end of the resistive element and the contact itself. Based on their construction materials, variable resistors can be classified into carbon-film, wire-wound, and solid-core types. According to the relationship between the input and output voltages and the rotation angle, they can also be categorized as linear variable resistors and function potentiometers. Consequently, variable resistors are widely used in electronic devices—particularly in receivers and audio systems—as volume controls.

Keywords： Introduction to the Types and Structural Characteristics of Adjustable Resistors