Temperature sensing

Figure Bl.27.8. Schematic view of Picker s flow microcalorimeter. A, reference liquid B, liquid under study P, constant flow circulating pump and 2, Zener diodes acting as heaters T and T2, thennistors acting as temperature sensing devices F, feedback control N, null detector R, recorder Q, themiostat. In the above A is the reference liquid and C2is the reference cell. When B circulates in cell C this cell is the working cell. (Reproduced by pemiission from Picker P, Leduc P-A, Philip P R and Desnoyers J E 1971 J. Chem. Thermo. B41.)...

SiHcon carbide s relatively low neutron cross section and good resistance to radiation damage make it useful in some of its new forms in nuclear reactors (qv). SiHcon carbide temperature-sensing devices and stmctural shapes fabricated from the new dense types are expected to have increased stabiHty. SiHcon carbide coatings (qv) may be appHed to nuclear fuel elements, especially those of pebble-bed reactors, or siHcon carbide may be incorporated as a matrix in these elements (153,154). 

In addition to the mercuiy-in-glass thermometer, other temperature-sensing elements may be used for psychrometers. These include resistance thermometers, thermocouples, bimetal thermometers, and thermistors. 

Temperature Measurement This is usually simple, and standard temperature-sensing elements are adequate for continuous use. Because of the high abrasion wear on horizontal protection tubes, vertical installations are frequently used. In highly corrosive atmospheres in which metallic protection tubes cannot be used, short, heavy ceramic tubes have been used successfully. 

Removal of liquid from phase that is a known thermal decomposition hazard ( strip-to-dryness ), i.e. liqiiid/solid level falls below temperature sensing device leading to overheating of thermally unstable material resulting in decomposition. 

Eaeh pressure- and temperature-sensing switeh should be in separate housings. The switeh type should be single-pole, double-throw, furnished... 

Temperature sensing points at various points along the tower shell are often a useful troubleshooting tool. Many... 

The physieal realization of a system to eontrol room temperature is shown in Figure 1.6. Flere the output signal from a temperature sensing deviee sueh as a thermoeouple or a resistanee thermometer is eompared with the desired temperature. Any differenee or error eauses the eontroller to send a eontrol signal to the gas solenoid valve whieh produees a linear movement of the valve stem, thus adjusting the flow of gas to the burner of the gas fire. The desired temperature is usually obtained from manual adjustment of a potentiometer. 

Temperature-sensing devices may also be used to measure flow in pipes or ducts and for level indication of... 

The design of the Pd-membrane reactor was based on the chip design of reactor [R 10]. The membrane is a composite of three layers, silicon nitride, silicon oxide and palladium. The first two layers are perforated and function as structural support for the latter. They serve also for electrical insulation of the Pd film from the integrated temperature-sensing and heater element. The latter is needed to set the temperature as one parameter that determines the hydrogen flow. 

Composition is another variable that is often measured indirectly. A temperature-sensing device is often used at the top of an atmospheric distillation... 

Vacuum distillation of parathion at above 100°C is hazardous, frequently leading to violent decomposition [1], Following a plant explosion, the process design was modified and featured a high degree of temperature sensing and control to avoid a recurrence [2],... 

Similar technology is also being used in induction hotplates and radiant heating elements and in the silicon nitride hotplates currently under development and which are characterized by an excellent heat transfer between heat source, sensor and saucepan. Gas hotplates could also be provided with the latest in domestic temperature sensing technology by fitting them with electric temperature control circuitry. 

It is not practical to stir all reaction systems, for example, bulk polymerizations, postpolymerization reactions, fixed-bed catalytic reactors, and plug-flow reactors. Although multipoint temperature sensing is often used as a key solution to determine a runaway in nonagitated vessels, the occurrence of hot spots may not always be detected. 

In a modem, automatic kettle, an electric heater warms the water inside the kettle - we call it the element . The electric circuit stops when the water reaches 100 °C because a temperature-sensing bimetallic strip is triggered. But the energy for a more old-fashioned, whistling kettle comes from a gas or a coal hob. The water boils on heating and converts to form copious amounts of gas (steam), which passes through a small valve in the kettle lid to form a shrill note, much like in a football referee s whistle. 

Infrared radiation has a very low energy and cannot eject electrons from most common photoemissive surfaces. The initial infrared sensors were temperature-sensing devices. Thermocouples and thermistors are forms of bolometers used for detecting infrared radiation. 

Temperature Recording. Use an accurate temperature-sensing device, such as a clinical thermometer or thermistor or similar probe, that has been calibrated to ensure an accuracy of 0.1° and has been tested to determine that a maximum reading is reached in less than 5 min. Insert the temperature-sensing probe into the rectum of the test rabbit to a depth of not less than 7.5 cm and, after a period of time not less than that previously determined as sufficient, record the rabbit s temperature. 

Other applications of the instrumentation and techniques here presented may include (i) temperature sensing employing alexandrite, ruby crystals, and Nd YAG crystals.(35 41) pH and partial pressure of carbon dioxide (pCCh) may be determined employing carboxy seminaphtorhodafluor (SNARF)-6.(42)... 

Of course, the temperature probes discussed could be further classified according to specific applications, e.g., biomedical temperature measurement, high temperature sensing up to >500°C, and the pyrometry range (> 500°C).The development of the temperature probes for such applications cited is discussed where specific applications are concerned. 

The use of fluorescence from alexandrite for temperature sensing was first reported by Augousti etal.(57,5S) using a low-power LED or a HeNe laser with a rather inefficient modulation accessory made of a bulky, high-voltage controlled Pockels cell,... 

In summary, the use of fluorescence lifetime monitoring for temperature sensing at high temperatures is based on the phenomenon of thermal quenching of fluorescence, while this phenomenon is j u st the very obstacle that blocks the extending of the measurement further into higher temperatures. Therefore, fluorescence thermometry is intrinsically more effective for measurement within moderate temperature regions, due to this fundamental nature of the fluorescence emission itself. 

K. T. V. Grattan, Fibre optic techniques for temperature sensing, in Fibre Optic Chemical Sensors and Biosensors, Vol. II (0. S. Wolfbeis, ed.), pp. 151-192, CRC Press, London (1991). 

A. R. Bugos, S. W. Allison, and M. R. Cates, Laser-induced fluorescent properties of europium-doped scandium orthophosphate phosphors for high-temperature sensing applications, Proc. of IEEE 1991 Southeast Conf, 1143-1147 (1991). 

Photodiode detectors have already been cited in this chapter in relation to near-IR fluorescence measurements on singlet oxygen,(8 16 18) in decay-time temperature sensing,(50) in liquid chromatography,(62) the study of proteins labelled with Nile Red,(64) and diode laser spectrometry,(67) Photodiodes are also conveniently packaged for many applications in an array form enabling rapid data acquisition e.g., in spectrophotometry, (35)... 

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