Infrared temperature measurements

A thermopile sensor generates an output voltage that depends on the temperature difference between its hot and cold contacts. For infrared temperature measurement, the hot contacts are normally thermally insulated and placed on a thin membrane, whereas the cold contacts are thermally connected to the metal housing. Infrared radiation, which is absorbed by the hot contacts of the thermopile, causes a temperature difference between hot and cold contacts. The resulting output voltage is a measure for the temperature difference between radiation source and cold contacts of the thermopile sensor. It is therefore necessary to measure also the temperature of the cold contacts by an additional ambient temperature sensor in order to determine the temperature of the radiation source. 

Young, A. M. "Infrared Temperature Measurement Essentials Performance Characteristics, Calibration and Testing." Industrial Heating LXV, no. 8 (1998) 45-60. 

N Renault, S Andre, D Maillet, and C Cunat. A spectral method for the estimation of a thermomechanical heat source from infrared temperature measurements. International Journal of Thermal Sciences, 49(8) 1394-1406, 2010. 

Figure 3.23 Online infrared temperature measurement system Raytek Corporation)...

At room temperature Vai = 10 pm (infrared) and at 6000 °K = 0.5 pm (green). The fact that the color of a body depends on its temperature is used in optical temperature measurements. This is often referred to as infrared temperature measurement even though some measurements may occur outside the infrared region of the spectrum. The infrared region ranges from a wavelength of 0.7 pm to about 400 pm. 

Temperature Distribution Measurement The temperature distribution in fuel cells can be of critical importance to the kinetics, electrolyte conductivity, material compatibility issues (high-temperature fuel cells), internal reformation process (high-temperature fuel cells), and other kinetic and transport phenomena known to be functionally dependent on temperature. Since the SOFC is dominated by the electrolyte resistance, which is a strong function of temperature, the current distribution in these systems closely follows the temperature profile. Several techniques can be used to measure the temperature distribution in a fuel cell. An embedded thermistor or thermocouple can be used when carefully placed. Additionally, infrared temperature measurement is a fascinating way to observe real-time temperature variation in a fuel cell. Infrared scanners can be used to look at temperature distribution in a specially modified single fuel cell and have been useful to see the phase change processes from ice to liquid in a low-temperature fuel cell [31]. 

This is perhaps one of the most difficult operations in mixing, and there have been no particular advances here for many years. Two types of tliermocouple have, and are still being, used. The first, and most widely used, utilises a strong thermocouple probe fitted with a thermocouple junction, and extending into the mixing chamber at some point. The second type is an infrared temperature measurement system, fitted to the mixer body to see into the mixing chamber. 

At various times, the use and accuracy of infrared temperature measurement has been extolled. This is very far from the truth, and accuracy and consistency has not been seen to be any better than the conventional thermocouple. Because of the requirements for a crystal window , location of an infrared thermometer has to be in one of the less severe mixing zones, resulting in a system life which is usually extended compared to conventional thermocouples. An infrared probe only measures a surface temperature the readings are therefore susceptible to the variations which can occur due to frictional heating of the mixing rubber surface, or alternatively to the effects of the cooled metal on the rubber surface from which it may have just parted. 

The deterrnination of surface temperature and temperature patterns can be made noninvasively using infrared pyrometers (91) or infrared cameras (92) (see Infrared technology and raman spectroscopy). Such cameras have been bulky and expensive. A practical portable camera has become available for monitoring surface temperatures (93). An appropriately designed window, transparent to infrared radiation but reflecting microwaves, as well as appropriate optics, is needed for this measurement to be carried out during heating (see Temperature measurement). 

The noncontact measurement principle, usually called optical or radiation temperature measurement, is based on detecting electromagnetic radiation emitted from an object. In ventilation applications this method of measurement is used to determine surface temperatures in the infrared region. The advantage is that the measurement can be carried out from a distance, without contact with the surface, which possibly influences the heat balance and the temperatures. The disadvantages are that neither air (or other fluid) temperature nor internal temperature of a material can be measured. Also the temper-... 

Short-lived molecules may often be identified by their infrared spectra measured at extremely low temperatures. In most cases, the experimental spectrum will be incomplete, although a few characteristic lines or bands are often sufficient to decide among alternative structures. 

Infrared (IR) thermography is one of the most advanced non-destructive (NDT) methods based on the fact that all bodies whose absolute temperature is above zero emit electromagnetic radiation over a wide spectrum of wavelengths depending on the temperature. Recently, several researchers have applied it to micro-scale temperature measurement. Hetsroni et al. (2001a) constructed a thermal micro-system... 

Hetsroni G, Gurevich M, Mosyak A, Rozenblit R (2003) Surface temperature measurement of a heated capillary tube by means of an infrared technique. Meas Sci Technol 14 807-814 Hetsroni G, Gurevich M, Mosyak A, RozenbUt R (2004) Drag reduction and heat transfer of surfactants flowing in a capillary tube. Int J Heat Mass Transfer 47 3797-3809 Hetsroni G, Mosyak A, Pogrebnyak E, Yaiin LP (2005) Eluid flow in micro-channels Int J Heat Mass Transfer 48 1982-1998... 

Fig. 9. Reaction of silica dried at 200°C with Zrfallylh. Infrared spectrum measured at room temperature,---SiCb,----Si02/Zr(allyl)i (16).

The other limit is the problem of temperature measurements. Classical temperature sensors could be avoided in relation to power level. Hence, temperature measurements will be distorted by strong electric currents induced inside the metallic wires insuring connection of temperature sensor. The technological solution is the optical fiber thermometers [35-39]. However, measurements are limited below 250 °C. For higher values, surface temperature can be estimated by infrared camera or pyrometer [38, 40], However, due to volumic character of microwave heating, surface temperatures are often inferior to core temperatures. 

Reaction of K3Co(CN) with PMMA. A 1.0 g sample of PMMA and 1.0g of the cobalt compound were combined in a standard vessel and pyrolyzed for 2 hrs at 375°C. The tube was removed from the oven and the contents of the tube were observed to be solid (PMMA is liquid at this temperature). The tube was reattached to the vacuum line via the break-seal and opened. Gases were determined by pressure-volume-temperature measurements on the vacuum line and identified by infrared spectroscopy. Recovered were 0.22g of methyl methacrylate and 0.11 g of CO and C02. The tube was then removed from the vacuum line and acetone was added. Filtration gave two fractions, 1.27g of acetone insoluble material and 0.30g of acetone soluble (some soluble material is always lost in the recovery process). The acetone insoluble fraction was then slurried with water, 0.11 g of material was insoluble in water. Infrared analysis of this insoluble material show both C-H and C-0 vibrations and are classified as char based upon infrared spectroscopy. Reactions were also performed at lower temperature, even at 260°C some char is evident in the insoluble fraction. 

Fig. 3.42 Body temperature measurement with an infrared ear thermometer.

The infrared ear thermometer is a major step in the development of thermometers for body temperature measurements. Compared to traditional mercury-in-glass or electronic contact thermometers it is more convenient, safer and faster. During its 10 years in the consumer market it has been gradually replacing conventional thermometers, especially for temperature measuring in children. 

Thermopiles are also used in new ear thermometers or in forehead thermometers to measure the infrared radiation emitted from the skin. This allows quick and reliable temperature measurement and is easy and comfortable to use. 

Figure 7. Schematic diagram of a photothermal deflection spectroscopy (PDS) apparatus for infrared- spectral measurements of surfaces at high temperatures and high pressures constructed at Utah by L.B. Lloyd.

A non-invasive infrared (IK) method has been developed for the measurement of temperatures of small moving fuel droplets in combustion chambers. 7111 The IR system is composed of two coupled off-axis parabolic mirrors and a MCT LWIR detector. The system was used to measure the temperature variations in a chain of monosized droplets generated with equal spacing and diameter (200 pm), moving at a velocity of >5 m/s and evaporating in ambient air. The system was also evaluated for droplet temperature measurements in flames under combustion conditions. 

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