rheostat

rheostat

a variable resistance, usually consisting of a coil of wire with a terminal at one end and a sliding contact that moves along the coil to tap off the current

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

Rheostat

An electrical device to vary the amount of resistance in a circuit and change the amount of current flowing through.

Illustrated Dictionary of Architecture Copyright © 2012, 2002, 1998 by The McGraw-Hill Companies, Inc. All rights reserved

rheostat

[′rē·ə‚stat]

(electricity)

A resistor constructed so that its resistance value may be changed without interrupting the circuit to which it is connected. Also known as variable resistor.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

rheostat

An electric device having a resistance which can be adjusted; used to control the flow of electric current, as, for example, in one type of dimmer.

McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.

variable resistor

An electronic component that is used to vary the amount of current that flows through a circuit. It works by sliding a wiper terminal across a resistive material, typically a thin film or chunk of carbon or a resistive wire made of nickel chromium or tungsten alloys. After being set to the appropriate location, the wiper's position often remains fixed on the circuit board; however, it can also be made user adjustable with a screwdriver.

Pots and Rheostats
Potentiometers and rheostats are variable resistors in which the wiper terminals take the form of a dial or slider that the user does manipulate, such as the volume control of a radio or music system. A rheostat is similar to a potentiometer, but handles more power. See resistor.

Variable Resistor

As the wiper is moved across the body of the device, the resistance increases between the wiper terminal and one end terminal and decreases between the wiper and the other end. (Image courtesy of Alltronics, www.alltronics.com)

A Potentiometer

Potentiometers are variable resistors commonly used to control the volume on a radio or music system. In this example, the dial controls the wiper in the device.

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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Rheostat

 

an electric device for controlling and limiting current or voltage in an electric circuit. The principal component of a rheostat is a conducting element with variable resistance. The magnitude of this resistance may be varied smoothly or in discrete steps. When it is necessary to vary the current or voltage within narrow limits, the rheostat is connected to the circuit in series; this is done, for example, when the starting current of electrical machines is to be limited. Potentiometer-connected rheostats are used to vary current or voltage over a wide range, from zero to a maximum value; in this case, the rheostat is a variable voltage divider.

According to their purpose, rheostats may be divided into such types as starting, starting-and-controlling, loading, and field rheostats. With respect to the method of heat dissipation, air-cooled, oil-cooled, and water-cooled types are distinguished. Depending on the material of the conductive element, rheostats are classified as metallic (most widely used), liquid, and carbon.

The simplest metallic rheostats are sliding-contact devices. In this design, the resistance is varied by moving a sliding contact finger along the turns of a wire made of a material of a high resistivity, such as manganin, constantan, nichrome, iron-chromium-aluminum alloy, or steel. The wire is wound on a cylindrical form made of an insulating material, such as porcelain or steatite.

A liquid rheostat consists of a vessel filled with an electrolyte in which electrodes are placed. The electrolyte is a 10–15 percent solution of Na₂CO₃ or K₂CO₃ in water. The resistance is varied by changing the distance between the electrodes or by changing the depth of immersion of the electrodes.

Carbon rheostats may be constructed in the form of piles of thin carbon disks. The resistance of such a rheostat is varied by changing the pressure applied to the piles.

REFERENCE

Chunikhin, A. A. Elektricheskie apparaty. Moscow, 1975.

T. N. DIL’DINA

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.