Pyrometer

An optical pyrometer
A sailor checking the temperature of a ventilation system.

A pyrometer is a type of remote-sensing thermometer used to measure the temperature of distant objects. Various forms of pyrometers have historically existed. In the modern usage, it is a device that from a distance determines the temperature of a surface from the amount of the thermal radiation it emits, a process known as pyrometry and sometimes radiometry.

The word pyrometer comes from the Greek word for fire, "πῦρ" (pyr), and meter, meaning to measure. The word pyrometer was originally coined to denote a device capable of measuring the temperature of an object by its incandescence, visible light emitted by a body which is at least red-hot.[1] Modern pyrometers or infrared thermometers also measure the temperature of cooler objects, down to room temperature, by detecting their infrared radiation flux.

Principle

It is based on the principle that the intensity of light received by the observer depends upon distance of observer from source and temperature of distant source. A modern pyrometer has an optical system and a detector. The optical system focuses the thermal radiation onto the detector. The output signal of the detector (temperature T) is related to the thermal radiation or irradiance of the target object through the Stefan–Boltzmann law, the constant of proportionality σ, called the Stefan–Boltzmann constant and the emissivity ε of the object.

This output is used to infer the object's temperature from a distance, with no need for the pyrometer to be in thermal contact with the object; most other thermometers (e.g. thermocouples and resistance temperature detectors (RTDs)) are placed in thermal contact with the object, and allowed to reach thermal equilibrium.

Pyrometry of gases presents difficulties. These are most commonly overcome by using thin filament pyrometry or soot pyrometry. Both techniques involve small solids in contact with hot gases.[citation needed]

History

A pyrometer from 1852. Heating the metal bar (a) presses against a lever (b), which moves a pointer (c) along a scale that serves as a measuring index. (e) is an immovable prop which holds the bar in place. A spring on (c) pushes against (b), causing the index to fall back once the bar cools.

The potter Josiah Wedgwood invented the first pyrometer to measure the temperature in his kilns,[2] which first compared the color of clay fired at known temperatures, but was eventually upgraded to measuring the shrinkage of pieces of clay, which depended on kiln temperature.[3] Later examples used the expansion of a metal bar.[4]

Technician measuring the temperature of molten silicon at 2650°F with a disappearing-filament pyrometer in Czochralski crystal growing equipment at Raytheon transistor plant in 1956.

The first disappearing-filament pyrometer was built by L. Holborn and F. Kurlbaum in 1901.[5] This device had a thin electrical filament between an observer's eye and an incandescent object. The current through the filament was adjusted until it was of the same colour (and hence temperature) as the object, and no longer visible; it was calibrated to allow temperature to be inferred from the current.[6]

The temperature returned by the vanishing filament pyrometer and others of its kind, called brightness pyrometers, is dependent on the emissivity of the object. With greater use of brightness pyrometers, it became obvious that problems existed with relying on knowledge of the value of emissivity. Emissivity was found to change, often drastically, with surface roughness, bulk and surface composition, and even the temperature itself.[7]

To get around these difficulties, the ratio or two-color pyrometer was developed. They rely on the fact that Planck's law, which relates temperature to the intensity of radiation emitted at individual wavelengths, can be solved for temperature if Planck's statement of the intensities at two different wavelengths is divided. This solution assumes that the emissivity is the same at both wavelengths[6] and cancels out in the division. This is known as the gray body assumption. Ratio pyrometers are essentially two brightness pyrometers in a single instrument. The operational principles of the ratio pyrometers were developed in the 1920s and 1930s, and they were commercially available in 1939.[5]

비파형계가 대중적으로 사용되면서 금속이 예시인 많은 물질들이 두 파장에서 같은 방출성을 가지지 않는 것으로 파악됐다.[8] 이러한 재료의 경우, 복사도가 취소되지 않고 온도 측정이 잘못되었다. 오차의 양은 측정이 이루어지는 파장과 복사도에 따라 달라진다.[6] 2색 비율의 파장계는 물질의 방사성이 파장에 의존하는지 여부를 측정할 수 없다.

방사성을 알 수 없거나 변화하는 실제 물체의 온도를 보다 정확하게 측정하기 위해, 다파장 파장 파이로미터가 미국 국립 표준 기술 연구소에서 구상되었고 1992년에 설명되었다.[5] 다파장 파이로미터는 3개 이상의 파장과 그 결과의 수학적 조작을 사용해 모든 파장에서 복사도를 알 수 없고 변화하며 다른 파장에서도 정확한 온도 측정을 시도한다.[6][9][8]

적용들

(1) 디스플레이. (2) 광학. (3) 광섬유 케이블 및 잠망경. (4) 피이미터 어댑터는 다음과 같은 i를 가지고 있다. 버슬 파이프 연결부. ii. Tuyere clamp. ii. 클램프 와셔. iv. 클램프 스터드 c/w 및 고정 하드웨어. v. 개스킷. vi. 노란다 투예르 소음기, 7세 밸브 시트. 8. 볼. (5) 공압 실린더: i. 내부 근접 스위치가 있는 스마트 실린더 어셈블리. ii. 가드 플레이트 조립체야 Temporary flange cover plate, used to cover periscope entry hole on tuyère adapter when no cylinder is installed on the tuyère. (6) Operator station panel. (7) Pyrometer light station. (8) Limit switches. (9) 4 conductor cab tire. (10) Ball Valve. (11) Periscope air pressure switch. (12) Bustle pipe air pressure switch. (13) Airline filter/regulat또는 (14) 방향 컨트롤 밸브, 서브 플레이트, 소음기 및 스피드 컨트롤 머플러. (15) 2" nom. 저압 공기 호스, 길이 40m.

파이로미터는 특히 움직이는 물체나 도달할 수 없거나 만질 수 없는 표면의 측정에 적합하다. 현대의 다경량 화로미터는 높은 정확도로 가스 터빈 엔진의 연소실 내부의 고온을 측정하는 데 적합하다.[10]

Temperature is a fundamental parameter in metallurgical furnace operations. Reliable and continuous measurement of the metal temperature is essential for effective control of the operation. Smelting rates can be maximized, slag can be produced at the optimum temperature, fuel consumption is minimized and refractory life may also be lengthened. Thermocouples were the traditional devices used for this purpose, but they are unsuitable for continuous measurement because they melt and degrade.

Measuring the combustion temperature of coke in the blast furnace using an optical pyrometer, Fixed Nitrogen Research Laboratory, 1930.

Salt bath furnaces operate at temperatures up to 1300 °C and are used for heat treatment. At very high working temperatures with intense heat transfer between the molten salt and the steel being treated, precision is maintained by measuring the temperature of the molten salt. Most errors are caused by slag on the surface which is cooler than the salt bath.[11]

The tuyère pyrometer is an optical instrument for temperature measurement through the tuyeres which are normally used for feeding air or reactants into the bath of the furnace.

A steam boiler may be fitted with a pyrometer to measure the steam temperature in the superheater.

A hot air balloon is equipped with a pyrometer for measuring the temperature at the top of the envelope in order to prevent overheating of the fabric.

Pyrometers may be fitted to experimental gas turbine engines to measure the surface temperature of turbine blades. Such pyrometers can be paired with a tachometer to tie the pyrometer output with the position of an individual turbine blade. Timing combined with a radial position encoder allows engineers to determine the temperature at exact points on blades moving past the probe.

See also

References

  1. ^ "incandescence". Dictionary.com. Dictionary.com, LLC. Retrieved 2 January 2015.
  2. ^ "History — Historic Figures: Josiah Wedgwood (1730 - 1795)". BBC. 1970-01-01. Retrieved 2013-08-31.
  3. ^ "Pyrometer". Wedgwood Museum. Retrieved 23 August 2013.
  4. ^ Draper, John William (1861). A Textbook on chemistry. Harper & Bros. p. 24. draper, john william.
  5. ^ a b c Michalski, L.; Eckersdorf, K.; Kucharski, J.; McGhee, J. (2001). Temperature Measurement. John Wiley & Sons. pp. 162–208. ISBN 978-0-471-86779-1.
  6. ^ a b c d Mercer, Carolyn (2003). Optical Metrology for Fluids, Combustion and Solids. Springer Science & Business Media. pp. 297–305. ISBN 978-1-4020-7407-3.
  7. ^ Ng, Daniel; Fralick, Gustave (2001). "Use of a multiwavelength pyrometer in several elevated temperature aerospace applications". Review of Scientific Instruments. 72 (2): 1522. Bibcode:2001RScI...72.1522N. doi:10.1063/1.1340558.
  8. ^ a b D. Olinger; J. Gray; R. Felice (2007-10-14). Successful Pyrometry in Investment Casting (PDF). Investment Casting Institute 55th Technical Conference and Expo. Investment Casting Institute. Retrieved 2015-04-02.
  9. ^ "Temperature sensors".
  10. ^ Mekhrengin, M.V.; Meshkovskii, I.K.; Tashkinov, V.A.; Guryev, V.I.; Sukhinets, A.V.; Smirnov, D.S. (June 2019). "Multispectral pyrometer for high temperature measurements inside combustion chamber of gas turbine engines". Measurement. 139: 355–360. Bibcode:2019Meas..139..355M. doi:10.1016/j.measurement.2019.02.084. S2CID 116260472.
  11. ^ Michalski, L.; Eckersdorf, K.; Kucharski, J.; McGhee, J. (2001). Temperature Measurement. John Wiley & Sons. pp. 403–404. ISBN 978-0-471-86779-1.

External links