Fiber-optical temperature sensors

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... 

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

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). 

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

J. Lin and C.W. Brown, Near-IR fiber-optic temperature sensor, Appl. Spectrosc., 47, 62-68 (1993). 

Fig. 16. Fiber-optic temperature sensor. A thin layer of silicon placed in the optical path exhibits a large change in refractive index with temperature, changing the effective path length. (Yazbak, Foxboro, Massachusetts)...

For both type of microwave reactors, if the reactor is not supplied with a temperature sensor or more likely accurate temperature measurment is prerequisited during an experiment, the fiber-optic temperature sensor is directly applied to the reaction mixture. In order to secure the sensor from harsh chemicals, the sensor is inserted into a capillary that in turn is inserted into the reaction mixture. In such a case, it is strongly advocated to use capillaries that are made of quartz glass and are transparent to microwave irradiation. Any capillary that is made of glass or even borosilicate glass can always slightly absorb microwave energy, in particular, while the reaction mixture does not absorb microwaves efficiently, and in turn lead to failures of fiber-optic thermometer performance. 

The electric field-stimulated uptake of macromolecules is temperature dependent whereas stimulated adsorption is not. For example, the uptake of BSA-FITC by COS 5-7 cells is almost completely diminished at 4°C and enhanced twofold at 37°C compared with room temperature. When elevating the temperature during exposure, one should take into account that LEF treatment also leads to temperature elevation in the cell suspension. The temperature of the solutions during exposure can be measured using fiber-optic temperature sensors (FISO Technologies, Quebec, Canada). Transient temperature rise by up to 2°C can be measured at the end of 1 min exposure of DMEM-H medium to LEF (20 V/cm, 180 (jls pulse duration, and 500 Hz frequency). 

Phillips, R.W. Tilstra, S.D. Design of a fiber optic temperature sensor for aerospace applications. In Temperature Its Measurement and Control in Science and Industry Schooley, J.F., Ed. American Institute of Physics New York, 1992 Vol. 6, Part 2, 721-724. 

Specialized microwave reactors for chemical synthesis are commercially available from such companies as CEM [20], Lambda Technologies [21], Microwave Materials Technologies (MMT), Milestone [22], PersonalChemistry [23], and Plazmatronika [24] which are mostly adjusted from microwave systems for digestion and ashing of analytical samples [25]. They are equipped with built-in magnetic stirrers and direct temperature control by means of an IR pyrometer, shielded thermocouple or fiber-optical temperature sensor, and continuous power feedback control, which enable one to heat reaction mixture to a desired temperature without thermal runaways. In some cases, it is possible to work under reduced pressure or in pressurized conditions within cavity or reaction vessels. 

The microwave equipment consisted of a microwave generator (85 W) and a tunable cavity operating in the TE mode, while temperature was monitored using a fiber-optic temperature sensor. The samples were maintained in a Teflon vessel of 1.5 cm diameter hole and 1.5 cm deep. During a typical run, 25 W of micro-wave power was required to heat the sample to the desired temperature over 80-200 s. It was demonstrated that microwave irradiation increased the rate of solution imidization over that obtained for conventional treatment by a factor of 20-34, depending on the reaction temperature. The apparent activation energy for this imidization, determined from an Arrhenius analysis, was reduced from 105 to 55 kj/mol when microwave activation was utilized rather than conventional thermal processing. 

Fig. 9.9 Laboratory-scale microwave-assisted freeze-drying equipment. 1, MWFD chamber 2, Fiber-optical temperature sensor 3, Vacuum breakage valve, for MWFD 4, Sample supporting plate ...

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. 

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 (-).

Fiber optic sensors are an alternative to thermocouples as embedded temperature distribution mapping sensors. As described in Section 2.2.7, McIntyre et al.104 developed two distinct fiber optic temperature probe technologies for fuel cell applications (free space probes and optical fiber probes). Both sensor technologies showed similar trends in fuel cell temperature and were also used to study transient conditions. 

One of the extraction vessels is equipped with a temperature and pressure sensor/control unit. Figure 3.10 shows the schematic diagram of a control vessel as well as a standard vessel. A fiber-optic temperature probe is built into the cap and the cover of the control vessel. The standard EPA method requires the microwave extraction system to be capable of sensing the temperature to within +2.5°C and adjusting the microwave field output power... 

Moreira ME, Carvalho ICS, Cao W, Bailey C, Taheri B, Palffy-Muhoray P (2004) Cholesteric liquid-crystal laser as an optic-fiber based temperature sensor. Appl Phys Lett 85 2691-2693... 

Miura N (1991) New-type calorimetric gas sensor using temperature characteristics of piezoelectric quartz crystal fitted with noble metal catalyst film. Sens Actuators B 5 211-217 Monz6n-Hemdndez D, Luna-Moreno D, Martfnez-Escobar D (2009) Fast response fiber optic hydrogen sensor based on palladium and gold nano-layers. Sens Actuators B 136 562-566 Mueller WM, Blackledge IP, Libowitz GG (1968) Metal hydrides. Academic, New York, NY Noh J-S, Lee JM, Lee W (2011) Low-dimensional palladium nanostmctures for fast and rehable hydrogen gas detection. Sensors 11 825-851... 

Fiber-optic chemical sensors offer several advantages over other sensing technologies based on the unique characteristics of optical fibers. The principal advantages include their immunity to harsh environmental conditions (e.g., electromagnetic interference, high temperature, high pH) and their ability to function without any direct electrical connection to the sample. These features have resulted in the development of different flber-optic chemical sensors for analytical applications in the clinical, environmental, and industrial fields. 

Udd E, Lawrence C M and Nelson D V, Development of a three axis strain and temperature fiber optical grating sensor . In Proc. SPIE - Smart Structures and Materials 1997 Smart Sensing, Processing, and Instrumentation, 1997,3042,229-36. 

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. 

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]. 

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