Temperature sensors, fiber-optic

A particularly difficult problem in microwave processing is the correct measurement of the reaction temperature during the irradiation phase. Classical temperature sensors (thermometers, thermocouples) will fail since they will couple with the electromagnetic field. Temperature measurement can be achieved either by means of an immersed temperature probe (fiber-optic or gas-balloon thermometer) or on the outer surface of the reaction vessels by means of a remote IR sensor. Due to the volumetric character of microwave heating, the surface temperature of the reaction vessel will not always reflect the actual temperature inside the vessel [7]. 

For optimum performance as strain and temperature sensors, embedded optical fibers should be mounted between two collincar plies and be aligned with the reinforcing fibers. Maximum sensitivity is achieved when fibers arc embedded as close to the surface of maximum tensile strain as possible, and sandwiched orthogonally between a pair ol ct>l-... 

Another early fiber optic refractive "sensor" was the one for measurement of temperature and salinity variations of sea water31. The sensing region consisted of a partly uncovered light guide. It detects salinity variations in water of known temperature, and temperature variations in water of known salinity with an accuracy of +/- 2 g/L and 1 °C, respectively, at NaCl concentrations of 300 g/L. 

Ivanov V.N., Ivanov S.V., Kel baHkhanov B.F., Klimova L.G., Trubnikov B.N., Chemyi V.V., Elisashvili D.T., Measurement of temperature and salinity variations of water with a fiber-optical sensor, Fizika Atmosfery i Okeana 1985 21 555. 

The design and implementation of a portable fiber-optic cholinesterase biosensor for the detection and determination of pesticides carbaryl and dichlorvos was presented by Andreou81. The sensing bioactive material was a three-layer sandwich. The enzyme cholinesterase was immobilized on the outer layer, consisting of hydrophilic modified polyvinylidenefluoride membrane. The membrane was in contact with an intermediate sol-gel layer that incorporated bromocresol purple, deposited on an inner disk. The sensor operated in a static mode at room temperature and the rate of the inhibited reaction served as an analytical signal. This method was successfully applied to the direct analysis of natural water samples (detection and determination of these pesticides), without sample pretreatment, and since the biosensor setup is fully portable (in a small case), it is suitable for in-field use. 

Temperature control Immersed fiber-optic probe (max. 300 °C) Outside IR remote sensor (optional)... 

Temperature measurement is achieved by means of a fiber-optic probe immersed in a single reference vessel. An available option is an IR sensor for monitoring the outside surface temperature of each vessel, mounted in the sidewall of the cavity about 5 cm above the bottom. The reaction pressure is measured by a pneumatic sensor connected to one reference vessel. Therefore, the parallel rotors should be filled with identical reaction mixtures to ensure homogeneity. 

Temperature measurement in the rotor systems is accomplished by means of an immersed fiber-optic probe in one reference vessel or by an IR sensor on the surface of the vessels positioned at the bottom of the cavity. Pressure measurement in HP-... 

Cavity size (volume) Approx. 50 L Delivered power 1500 W Max. output power 1200 W Temperature control Outside IR remote sensor Immersed fiber-optic probe (optional) Pressure measurement Pneumatic pressure sensor (optional) Cooling system Air flow through cavity 100 m3 h1 External PC Optional not required as integrated key panel is standard equipment ... 

Routine temperature measurement within the Discover series is achieved by means of an IR sensor positioned beneath the cavity below the vessel. This allows accurate temperature control of the reaction even when using minimal volumes of materials (0.2 mL). The platform also accepts an optional fiber-optic temperature sensor system that addresses the need for temperature measurement where IR technology is not suitable, such as with sub-zero temperature reactions or with specialized reaction vessels. Pressure regulation is achieved by means of the IntelliVent pressure management technology. If the pressure in the vial exceeds 20 bar, the... 

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. 

Preliminary research has shown that Brillouin fiber-optic sensing systems provide a possible method to detect leaks and third-party intrusion on a pipeline over distances of 25 km or more. Their intrinsic response to both temperature and mechanical strain allows for the separation of these parameters and the detection of anomalies in the scan profiles. In addition, the same sensor could be integrated into the pipeline system to detect possible ground movement relative to fixed reference points. Limited test results on surface loads associated with the intrusion of vehicles and people on a pipeline have demonstrated the sensitivity of the system and its ability to discriminate loads at different soil depths. 

Li, E. Wang, X. Zhang, C., Fiber optic temperature sensor based on interference of selective higher order modes, Appl. Phys. Lett. 2006, 89, 091119... 

Freifeld, B.M., Finsterle, S., Onstott, T.C., Toole, P., Pratt, L.M. 2008. Ground surface temperature reconstructions using in situ estimates for thermal conductivity acquired with a fiber-optic distributed thermal perturbation sensor. Geophysical Research Letters, 35, L14309,... 

Intrinsically conducting polymers, 13 540 Intrinsic bioremediation, 3 767 defined, 3 759t Intrinsic detectors, 22 180 Intrinsic fiber-optic sensors, 11 148 Intrinsic magnetic properties, of M-type ferrites, 11 67-68 Intrinsic photoconductors, 19 138 Intrinsic rate expressions, 21 341 Intrinsic semiconductors, 22 235-236 energy gap at room temperature, 5 596t Intrinsic strength, of vitreous silica, 22 428 Intrinsic-type detectors, cooling, 19 136 Intrinsic viscosity (TV), of thermoplastics, 10 178... 

Figure 9.14. Precision and accuracy of the instrument at various concentrations of oxygen as compared to a standard oxygen analyzer (Servomex). The fiber optic sensor monitored the concentration of oxygen in saline solution (continuous stair) in equilibrium with various nitrogen-oxygen gas mixtures monitored by the gas analyzer (dotted staircase). The absolute concentration of oxygen in the gas phase is about 60 times larger than the corresponding equilibrium concentration in the liquid phase. The bath temperature was 37 C For the purpose of comparison both measurements have been scaled to percent oxygen. (From Ref. 21 with permission.)...

Figure 9.16. Performance of alexandrite based real time optical temperature sensors versus standard (Neslab RTE-J l IM) Equation 9.107 is used to obtain a working relation between Temperature and r. The fiber optic sensor monitored the bath temperature (—) in equilibrium with the standard (-).

Z. Zhang, K. T. V. Grattan, and A.W. Palmer, Fiber-optic high-temperature sensor based on the fluorescence lifetime of alexandrite, Rev. Sci. Instrum. 63, 3869-3873 (1992). 

K. T. V. Grattan, R. K. Selli, and A. W. Palmer, Ruby fluorescence wavelength division fiber-optic temperature sensor, Rev. Sei. Instrum. 57, 1231-1234 (1987). 

Fiber Optic Sensor Devices for Temperature Measurement... 

Table 11.1. Various Fiber Optic Temperature Sensor Schemes...

A variety of fiber optic thermometry systems using fluorescence sensors have been discussed or become available over the past years. Most of the earliest systems are based on the temperature-dependent fluorescence intensity of appropriate materials. One such example of an early commercial system is the Luxtron model 1000, shown in Figure 11.2, which utilized europium-activated lanthanum and gadolinium... 

In the system which uses crystalline alexandrite as the sensor material/381 a measurement reproducibility of 1 °C is achieved over a wide temperature region from 20 to 700°C. The same technique is applied to another fiber optic thermometer system which is designed for biomedical sensing applications and uses LiSrAlF6 Cr3+ as sensor material/391 The standard deviation of the measurement recorded by this system is better than 0.01°C within the 20 Cand 50°C region. 

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