gas actuated thermometers work on pressure or volume change of a gas

7/27/2019 Gas Actuated Thermometers Work on Pressure or Volume Change of a Gas

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Gas Actuated Thermometers work on pressure or volume change of a gas. That means the temperature of a body is defined

by the thermic expansion (the measurement of length or volume change).

The filling compound is located in a vessel. The temperature change causes a system pressure increase or drop that can be

read off the scale by using a bourdon tube pressure system

From Measurement and Control Basics Four th Edition

Many physical properties change with temperature, such as the volume of

a liquid, the length of a metal rod, the electrical resistance of a wire, the

pressure of a gas kept at constant volume, and the volume of a gas kept at

constant pressure. Filled-system thermometers use the phenomenon of

thermal expansion of matter to measure temperature change.

The filled thermal device consists of a primary element that takes the form

of a reservoir or bulb, a flexible capillary tube, and a hollow Bourdon tube

that actuates a signal-transmitting device and/or a local indicating temperature

dial. A typical filled-system thermometer is shown in Figure 7-1.

In this system, the filling fluid, either liquid or gas, expands as temperature

increases. This causes the Bourdon tube to uncoil and indicate the

temperature on a calibrated dial.

The filling or transmitting medium is a vapor, a gas, mercury, or another

liquid. The liquid-filled system is the most common because it requires a

bulb with the smallest volume or permits a smaller instrument to be used.

The gas-filled system uses the perfect gas law, which states the following

for an ideal gas:

T = kPV (7-5)

where:


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T = temperature

k = constant

P = pressure

V = volume

If the volume of gas in the measuring instrument is kept constant, then the

ratio of the gas pressure and temperature is constant, so that

(7-6)

The only restrictions on Equation 7-6 are that the temperature must be

expressed in degrees Kelvin and the pressure must be in absolute units.

Example 7-3 shows how to calculate the temperature for a change in pressure

of a fixed volume temperature detector.

A gas thermometermeasurestemperatureby the variation in volume or pressure of a gas.[1]

One

common apparatus is a constant volume thermometer. It consists of a bulb connected by a capillary

tubeto amanometer. The bulb is filled with a gas such that the volume of the gas in the bulb remains

constant. The volume is related to temperature by k, known as Charles's Law. The pressure of the gas in

the bulb can be obtained by measuring the level difference in the two arms of the manometer.[2]

Gas

thermometers are often used to calibrate otherthermometers.[3]

Two variants of a gas thermometer
http://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Temperaturehttp://en.wikipedia.org/wiki/Gas_thermometer#cite_note-1http://en.wikipedia.org/wiki/Gas_thermometer#cite_note-1http://en.wikipedia.org/wiki/Gas_thermometer#cite_note-1http://en.wikipedia.org/wiki/Capillary_tubehttp://en.wikipedia.org/wiki/Capillary_tubehttp://en.wikipedia.org/wiki/Capillary_tubehttp://en.wikipedia.org/wiki/Capillary_tubehttp://en.wikipedia.org/wiki/Manometerhttp://en.wikipedia.org/wiki/Manometerhttp://en.wikipedia.org/wiki/Manometerhttp://en.wikipedia.org/wiki/Charles%27s_Lawhttp://en.wikipedia.org/wiki/Charles%27s_Lawhttp://en.wikipedia.org/wiki/Charles%27s_Lawhttp://en.wikipedia.org/wiki/Gas_thermometer#cite_note-2http://en.wikipedia.org/wiki/Gas_thermometer#cite_note-2http://en.wikipedia.org/wiki/Gas_thermometer#cite_note-2http://en.wikipedia.org/wiki/Thermometerhttp://en.wikipedia.org/wiki/Thermometerhttp://en.wikipedia.org/wiki/Gas_thermometer#cite_note-3http://en.wikipedia.org/wiki/Gas_thermometer#cite_note-3http://en.wikipedia.org/wiki/Gas_thermometer#cite_note-3http://en.wikipedia.org/wiki/File:Plinski-termometer2.pnghttp://en.wikipedia.org/wiki/File:Plinski-termometer2.pnghttp://en.wikipedia.org/wiki/File:Plinski-termometer2.pnghttp://en.wikipedia.org/wiki/File:Plinski-termometer2.pnghttp://en.wikipedia.org/wiki/File:Plinski-termometer2.pnghttp://en.wikipedia.org/wiki/File:Plinski-termometer2.pnghttp://en.wikipedia.org/wiki/Gas_thermometer#cite_note-3http://en.wikipedia.org/wiki/Thermometerhttp://en.wikipedia.org/wiki/Gas_thermometer#cite_note-2http://en.wikipedia.org/wiki/Charles%27s_Lawhttp://en.wikipedia.org/wiki/Manometerhttp://en.wikipedia.org/wiki/Capillary_tubehttp://en.wikipedia.org/wiki/Capillary_tubehttp://en.wikipedia.org/wiki/Gas_thermometer#cite_note-1http://en.wikipedia.org/wiki/Temperature


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galvanometer, instrument for measuring a small electrical current or a function of the current by

deflection of a movingcoil. The deflection is a mechanical rotation derived from forces resulting from

the current.

The most common type is theDArsonval galvanometer, in which the indicating system consists of a

light coil of wire suspended from a metallic ribbon between the poles of a permanent magnet.

Themagnetic fieldproduced by a current passing through the coil reacts with the magnetic field of

the permanent magnet, producing a torque, or twisting force. The coil, to which an indicating needle

or mirror is attached, rotates under the action of the torque; the angle through which it rotates

tobalancethe torsion of the suspension provides a measure of the current flowing in the coil. The

angle is measured by the movement of the needle or by the deflection of a beam of light reflected

from the mirror.

Theballistic galvanometeris designed to deflect its indicating needle (or mirror) in a way that is

proportional to the total charge passing through its moving coil or to a voltage pulse of short

duration. Any conventional galvanometer may also be employed as a ballistic type, but the latter has

smaller torque and higher inertia in the coil.
http://www.britannica.com/EBchecked/topic/124676/coilhttp://www.britannica.com/EBchecked/topic/124676/coilhttp://www.britannica.com/EBchecked/topic/124676/coilhttp://www.britannica.com/EBchecked/topic/151833/dArsonval-galvanometerhttp://www.britannica.com/EBchecked/topic/151833/dArsonval-galvanometerhttp://www.britannica.com/EBchecked/topic/151833/dArsonval-galvanometerhttp://www.britannica.com/EBchecked/topic/357048/magnetic-fieldhttp://www.britannica.com/EBchecked/topic/357048/magnetic-fieldhttp://www.britannica.com/EBchecked/topic/357048/magnetic-fieldhttp://www.britannica.com/EBchecked/topic/49765/balancehttp://www.britannica.com/EBchecked/topic/49765/balancehttp://www.britannica.com/EBchecked/topic/49765/balancehttp://www.britannica.com/EBchecked/topic/50664/ballistic-galvanometerhttp://www.britannica.com/EBchecked/topic/50664/ballistic-galvanometerhttp://www.britannica.com/EBchecked/topic/50664/ballistic-galvanometerhttp://www.britannica.com/EBchecked/topic/50664/ballistic-galvanometerhttp://www.britannica.com/EBchecked/topic/49765/balancehttp://www.britannica.com/EBchecked/topic/357048/magnetic-fieldhttp://www.britannica.com/EBchecked/topic/151833/dArsonval-galvanometerhttp://www.britannica.com/EBchecked/topic/124676/coil

gas actuated thermometers work on pressure or volume change of a gas

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