Fiber optic temperature probe

A variety of optical alignment accessories for the launch of the excitation light into the fiber optic temperature probe, the collection of the fluorescence response, and optical filters used to isolate the excitation and fluorescence emission at the detector and in some cases at the excitation source as well. 

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... 

Equipment Single mode microwave synthesizer configured for manual peptide synthesis equipped with a fiber optic temperature probe (Discover SPS microwave-assisted peptide synthesizer, GEM Corporation) (rrr Note 1). 

K. T. V. Grattan, A. W. Palmer, and Z. Zhang, Development of a high-temperature fiber-optic thermometer probe using fluorescent decay, Rev. Sci. Instrum. 62(5), 1210-1213. 

The investigator who wants to make an EDL is thus faced with a very large amount of information dispersed in the literature and finds it very difficult to reproduce these procedures to develop EDL with the properties desired. An experimental vacuum system for EDL (Hg, Hgl2, Cd, T, KI, P, Se, S) manufacture has recently been designed by Cirkva and coworkers (Fig. 19.4) [58]. The technique is very simple and enables the preparation of EDL in a conventional chemistry laboratory. Examples of EDL are shown in Fig. 19.5. EDL performance is tested to prepare the lamps for spectral measurements [58]. A typical experimental system for such testing comprises a round-bottomed flask, placed in a MW oven, containing n-heptane and equipped with fiber-optic temperature measurement, a spectral probe, and a Dimroth condenser (Fig. 19.6). 

In the fiber-optic thermometry probe technique, a temperahue sensor, consisting of a small amount of a temperature-sensitive material (manganese-activated magnesium fluorogermanate), is mounted on the end of a probe and is placed on the surface of the device under test (DUT). A filtered xenon flash lamp provides a blue-violet light to excite the phosphor on the probe to fluoresce. When excited by this wavelength of light, the phosphor in the sensor exhibits a deep red fluorescence. 

The fiber-optic thermometry probe technique can measure temperatures with accuracies of 0.1°C. Using the smallest probe, this probing technique can measure temperatures of 0.001-in. spot sizes. After the DUT has reached thermal equilibrium, the system can make up to four measurements per second. To accurately measure junction temperature, the device must be unencapsulated and unsealed. The probe is placed on the junction. 

Reflective probes may be used over the entire rang of particle concentrations, from extremely dilute flows to the fixed bed state for several powder types in gas or liquid media, once they have been suitably calibrated [63, 85, 166, 238]. These probes are also nearly free of interference by temperature, humidity, electrostatics and electromagnetic fields. Lischer and Louge [116] developed a reflective F-OPT specifically for measuring solids concentration. In the fiber optical reflection probe developed by Hartge et al. [82], the emitted light from a laser diode reaches the... 

These results provide clear evidence for the existence of selective heating effects in MAOS involving heterogeneous mixtures. It should be stressed that the standard methods for determining the temperature in microwave-heated reactions, namely with an IR pyrometer from the outside of the reaction vessel, or with a fiber-optic probe on the inside, would only allow measurement of the average bulk temperature of the solvent, not the true reaction temperature on the surface of the solid reagent. 

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]. 

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. 

CombiCHEM System (Fig. 3.9) For small-scale combinatorial chemistry applications, this barrel-type rotor is available. It can hold two 24- to 96-well microtiter plates utilizing glass vials (0.5-4 mL) at up to 4 bar at 150 °C. The plates are made of Weflon (graphite-doped Teflon) to ensure uniform heating and are sealed by an inert membrane sheet. Axial rotation of the rotor tumbles the microwell plates to admix the individual samples. Temperature measurement is achieved by means of a fiber-optic probe immersed in the center of the rotor. 

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 ... 

Figure 11.15. Schematics of the optical arrangement and temperature probes for the Cr+ fluorescence lifetime-based fiber optic thermometers. F = short-pass optical filter Fa = bandpass or long-pass optical filter LD = laser diode LED = light emitting diode S = the fluorescence material used as sensing element vm = signal to modulate the output intensity of the excitation light source v/= the detected fluorescence response from the sensing element.

Fiber optic fluorescence thermometry can provide several quite flexible approaches to access the required measurement regions. The temperature probes can be... 

The subsequent development of laser diode sources at low cost, and improved electronic detection, coupled with new probe fabrication techniques have now opened up this field to higher-temperature measurement. This has resulted in an alexandrite fluorescence lifetime based fiber optic thermometer system,(38) with a visible laser diode as the excitation source which has achieved a measurement repeatability of l°C over the region from room temperature to 700°C, using the lifetime measurement technique. 

In the worse case, where either sample temperature, pressure or reactor integrity issues make it impossible to do otherwise, it may be necessary to consider a direct in situ fiber-optic transmission or diffuse reflectance probe. However, this should be considered the position of last resort. Probe retraction devices are expensive, and an in situ probe is both vulnerable to fouling and allows for no effective sample temperature control. Having said that, the process chemical applications that normally require this configuration often have rather simple chemometric modeling development requirements, and the configuration has been used with success. 

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