thermostat


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Related to thermostat: thermocouple

thermostat,

automatic device that regulates temperature in an enclosed area by controlling heating or refrigerating systems. It is commonly connected to one of these systems, turning it on or off in order to maintain a predetermined temperature. Its operating principle is based on the fact that one of its components expands or contracts significantly during a temperature change. This expansion or contraction actuates a control on a furnace, cooling system, or piece of machinery. The thermostat sometimes uses mercury, which expands when heated and rises in a glass tube until, at a predetermined point, it touches an electrical contact to complete a circuit and thereby actuate a control; conversely, during a lowering of temperature the mercury descends in the tube and breaks the circuit. The thermostat often uses a bimetallic strip, which is made of two thin metallic pieces of different composition that are bonded together. As the temperature of the strip changes, the two pieces change length at different rates, forcing the strip to bend. This bending causes the strip to make or break a circuit.
The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/

Thermostat

An instrument, electrically operated, such as a bimetal strip, for automatically maintaining a constant temperature; commonly used in conjunction with heating and air-conditioning plants.
Illustrated Dictionary of Architecture Copyright © 2012, 2002, 1998 by The McGraw-Hill Companies, Inc. All rights reserved
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Thermostat

 

(constant-temperature chamber), a device for maintaining a constant temperature. A thermostat is a vessel made of metal, glass, or other material, and it is thoroughly protected by heat insulation against environmental influences.

The constancy of temperature in a thermostat is provided by thermoregulators or by a phase transition, such as the melting of ice, the boiling of water, or the solidification of a eutectic, that takes place at a specific temperature. When the difference between the ambient temperature and the temperature in the thermostat is small, the temperature of the working agent (a gas or liquid) that fills the thermostat remains constant. The object whose properties are being studied at a given temperature is in thermal contact with the working agent, whose temperature it acquires.

Thermostats filled with a working agent are usually equipped with a quick-response heater or cooler, an automatic thermoregulator of the required precision, and a mechanism that vigorously mixes the working agent to ensure rapid equalization of the temperature in the thermostat. Liquid-filled thermostats may contain alcohol (for temperatures from –60° to 10°C), water (10°–95°C), oil (100°–300°C), and salt or saltpeter (300°–500°C). Gas-filled thermostats with the same range of temperatures are used less frequently because of the difficulty in ensuring thermal contact with the object being studied.

Low heat exchange with the environment is provided in high-temperature and low-temperature thermostats. The object being studied is kept at a constant temperature under adiabatic conditions—that is, there is no working agent. In low-temperature thermostats, heat is supplied or removed by a special “thermal key”—a heat-conducting rod. An electric furnace with a thermoregulator and a heavy metal unit into which the object of study is placed is frequently used as a thermostat at high temperatures (300°–1200°C). A thermostat for the maintenance of low temperatures is called a cryostat.

In thermodynamics, a system whose heat capacity is so great that the quantities of heat supplied to it do not alter its temperature is often called a thermostat.

REFERENCES

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

thermostat

[′thər·mə‚stat]
(engineering)
An instrument which measures changes in temperature and directly or indirectly controls sources of heating and cooling to maintain a desired temperature. Also known as thermorelay.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

thermostat

An instrument which responds to changes in temperature, and directly or indirectly controls temperature.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.

thermostat

A device that maintains the desired temperature in a system.
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved

thermostat

a device that maintains a system at a constant temperature. It often consists of a bimetallic strip that bends as it expands and contracts with temperature, thus breaking and making contact with an electrical power supply
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
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As soon as the Nest Learning thermostat is installed, consumers have to simply use it like a manual thermostat: Turn the temperature up when they wake up; down when they leave the house; back up when they come home; and finally down for the rest of the night.
Latest research from the Energy Saving Trust shows that if all households in Wales reduced their thermostats to a steady 18 degrees Celsius, over pounds 50 million would be saved on energy bills in Wales alone in one year.
3) Most people's thermostats are set higher than they need to be to keep comfortably warm.
c) Turning a room thermostat to the limit of its range does not cause the room to heat up faster.
The Wireless Pneumatic Thermostat system uses the Open Automated Demand Response Communication Standard, developed by the US Department of Energy's Lawrence Berkeley National Laboratory.
* A flexible thermostat, for conventional and heat-pump applications, which means just one part to stock.
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New luxury apartments on the Thames opposite the Millennium Dome are equipped with DEVI's leading intelligent underfloor heating and thermostat control system.