Ratio pyrometers

The problem of emissivity from real materials has stimulated the study of pyrometers that measure radiation at two different wavelengths. The principle of the two-color pyrometer is that the energy radiated from a source of one wavelength increases with temperature at a rate different from that radiated at another wavelength. Thus temperature can be deduced from the ratio of the intensities at the two wavelengths, regardless of emissivity. Two-color pyrometers are not widely used. 

Ratio Pyrometers The ratio pyrometer is also called the two-color pyrometer. Two different wavelengths are utilized for detecting the radiated signal. If one uses Wien s law for small values of XT, the detected signals from spectral radiant energy flux emitted at the wavelengths and 2 with emissivities and are... 

The gas turbine eontrol loop eontrols the Inlet Guide Vanes (IGV) and the Gas Turbine Inlet Temperature (TIT). The TIT is defined as the temperature at the inlet of the first stage turbine nozzle. Presently, in 99% of the units, the inlet temperature is eontrolled by an algorithm, whieh relates the turbine exhaust temperature, or the turbine temperature after the gasifier turbine, the eompressor pressure ratio, the eompressor exit temperature, and the air mass flow to the turbine inlet temperature. New teehnologies are being developed to measure the TIT direetly by the use of pyrometers and other speeialized probes, whieh eould last in these harsh environments. The TIT is eontrolled by the fuel flow and the IGV, whieh eontrols the total air mass... 

Ratio Pyrometers The ratio pyrometer is also called the two-color pyrometer. Two different wavelengths are utilized for detecting... 

In ratio pyrometers [5], a device is designed to measure the spectral radiance temperatures and 7, at two wavelengths and X. Then, the true temperature Tm is determined from the ratio temperature Tra and is given by... 

However, the emissivity ratio er is still an unknown quantity for some materials. Therefore, the ratio pyrometer is commonly used for temperature measurements on materials that can be assumed to be gray with er assumed equal to unity. 

To overcome the problems faced by the single-wavelength radiation thermometer and the ratio pyrometer, a double-wavelength radiation thermometer (DWRT) measures the spectral radiance itself at two distinct wavelengths for surface temperature evaluation. For this method to be used, the emissivity compensation function e i = fl v) must be defined. A detailed description of the principle for DWRT can be found in Ref. 53. When the emissivity relation x.i = Ae ) at two distinct wavelengths e i = fl v) is established, the true temperature on the measured surface can be determined from the inferred temperature, which is defined as... 

Absorption ratio and pyrometer temperature measurements. Time histories (L) (Lighter Traces 30 second average. Darker Traces 30 minute moving average) (Reprinted from Teichert, H., Fernholz, T, and Ebert, V., "Simultaneous In Situ Measurement of CO, H2O, and Gas Temperatures in a Full-Sized Coal-Fired Power Plant by Near-Infrared Diode Lasers," Applied Optics 42,2043-51,2003. With permission.) and temperature versus absorption rate (R). 

Ratio pyrometers are a variation of narrowband pyrometers used to reduce the influence of the emissivity of the object being measured (they are especially useful in cases where the emissivity varies with time). The intensity of radiation is measured at two wavelengths (A.i and A.2) and Planck s law is used ... 

Pyrometry When the temperatures of interest are in a suitable range, pyrometry is the best technique for measuring the temperature of the Knudsen cell vapor sources in KEMS instruments. Some of the major advantages are that it is a noncontact technique, with the pyrometer placed outside the furnace and vacuum chamber. Also, one pyrometer can be used to measure temperature at multiple locations, which improves the consistency of calibration. The key advantage is that pyrometry, as stated in the Temperature Measurement section, is based on the Planck radiation law, which in ratio form defines ITS-90 at all temperatures above the Ag fixed point (1234.93 K).Thus,pyrometry is the standard method for realizing thermodynamic temperature through the use of Equation 48.10 ... 

To avoid the uncertainties of temperature measurement associated with the uncertainty of emissivity, a two-color pyrometer is recommended, which analyzes the body radiation properties for two wavelengths. In the two-color or ratio pyrometer the radiation is detected at two separate wavelengths for which emis-sivities of the surface can be considered nearly the same. Thus the ratio of the thermal radiation sensor output calculated for two wavelengths by Wien s law is obtained as... 

All alloys in the system were single phase and had hep structure at room temperature. The solidus temperature for each alloy was determined in vacuum using a calibrated optical pyrometer focused on a 1 mm hole drilled to a depth of 3-4 mm in an attempt to achieve black body conditions (normally a 10 1 ratio of depth to diameter is required for black body conditions). 

Difficulties in reliable temperature measurement preclude automatic control. The maximum temperature is limited by the wear rate of the refractory and the minimum temperature by the carbon conversion [70]. Typically, temperature is adjusted using the O/C ratio, which is highly sensitive to the coal rank, slurry concentration, and the quantity and composition of the recycled solids. However, an on-line measurement of the latter parameters is often not possible. Pyrometers lack optical access because of slag deposition [70]. The temperature can be measured indirectly using the CH4 yield or CO/CO2 ratio [71]. Finally, thermocouples immersed in the refractory must be used these indicate temperatures, which are lower than is actually the case, and are sensitive to the insulating effects of the slag film [70]. 

Mikron M90, MIS, GAS, M120,M125, and Quantum 1 Various models, including ratio pyrometers, from 0 to +3000°C, LCD displays. Options laser aiming light, telescope, e set, various FOVs. Quantum 1 has laser reflection emissivity calculation and correction feature for high-speed targets. 

Technology (now part of Mikron) Heat switch (Solar TDIOO and Meteor 300), Pulsar, and Quasar series Various heat pulse switches and ruggedized models from 260-1650°C, including ratio pyrometers. 

Ircon Modline 3 and 4 series SA, SR, and 1100 series Javelin, Mirage, and MiniIRT series others Various models and accessories, -18 to +1375°C, integrated, fixed focus, 2-wire transmitters, spectral selection. Various models of 2-piece, -18 to +3600°C with thru-lens sights, LCD display, spectral selection (including ratio pyrometers), and control and output options. IR pulse switches and fiber optic coupled heads. 

M68, M668, M600, M680 M770, M780, MI series Fiber optic, one color and ratio pyrometers, ranges from 250-3500°C. 

Marathon series For high-temperature applications, up to 3000°C, 1 pm spectral region, include ratio pyrometer and fiber optic coupled models. 

Williamson (continued) TempMatic 4000, FiberView 5000, 500, 700, and 1000 series, TransTemp series Various models ranges from 30-2500°C 2-wire, fixed focus transmitters 2-wire, fixed focus, single-wavelength and ratio pyrometers some fiber optic coupled models. 

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