Application Notes on Rheostats and Potentiometers.

Potentiometers, rheostats and trimmers are three-terminal resistors that are used to measure or divide voltages, and to protect or control circuits. Potentiometers are variable resistors that are adjusted with a knob or dial. Rheostats and trimmers are types of potentiometers. With a rheostat, a third “wiper” terminal is shorted to one of two fixed terminals. The wiper terminal has a resistance which varies with its position, and the two fixed terminals are connected by a fixed resistance. Trimmers are factory-set devices that require infrequent adjustments. They feature a slotted, actuator-type style and can be adjusted with a special tool or screwdriver. Other types of potentiometers, rheostats and trimmers are also available. These include standard potentiometers, mechanical devices in which the output resistance is set by a shaft; and digital potentiometers, which set an output resistance by sending a digital signal through an electrical interface.
Potentiometers, rheostats and trimmers carry specifications for potentiometer category and actuator configuration. Industrial-grade potentiometers are protected by an enclosure, typically one that is rated by the National Electrical Manufacturers Association (NEMA). Typically, industrial-grade products are gear-driven and have connector outputs. These potentiometers, rheostats and trimmers resist the ingress of dirt and dust, and last longer than unenclosed potentiometers. Discrete-board components, another potentiometer category, are also commonly available. In terms of actuator configuration, choices include single-turn, multi-turn, and slide. With single-turn devices, the shaft rotation is limited to less than or equal to 360 degrees. By contrast, multi-turn potentiometers, rheostats and trimmers can be rotated multiple times, with as many as 15 or 20 turns from stop to stop. Slide-actuated products require the user to move a handle instead of rotating a knob.
Potentiometers, rheostats and trimmers differ in terms of construction, mounting or packaging, performance specifications and features. Choices for construction include ceramic composition, carbon composition, carbon film, cermet, thick film, thin film, metal alloy, metal film, and metal oxide. Wirewound resistors are also available. There are many mounting and packaging styles for potentiometers, rheostats and trimmers. Choices include surface mount technology (SMT), bolt-on or chassis, panel mount, through-hole technology (THT), axial leads, gull-wing leads, J-leads, radial leads, screw terminals and tab terminals. The most important performance specifications to consider when selecting potentiometers, rheostats and trimmers include resistance range, tolerance, operating alternating current (AC) voltage, operating direct current (DC) voltage, and operating temperature.
Sebastian

G.M. Technical

Nunes Instruments

645 Hundred Feet Road,

Coimbatore. 641012.

Tamil Nadu

India,

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