Remote optical

The instrumentation for sensors based on absorption measurements can be designed on the traditional spectrophotometers by using a flowthrough cell for automatic sampling with the sensors mounted inside the flow-through cell shown in Fig. 20a.3. For remote optical sensing using optical fibers, the chromophores can be immobilized in reflective... 

Chemical equilibrium and analysis of a mixture. A remote optical sensor for C02 in the ocean was designed to operate without the need for calibration.21 The sensor compartment is separated from seawater by a silicone membrane through which C02, but not dissolved ions, can diffuse. Inside the sensor, C02 equilibrates with HCO3 and CO3-. For each measurement, the sensor is flushed with fresh solution containing 50.0 pM bromothymol blue indicator (NaHIn) and 42.0 pM NaOH. All indicator is in the form HIn-or In2 near neutral pH, so we can write two mass balances (1) [HIn ] + [In2-] = Fln = 50.0 pM and (2) [Na"] = FNa = 50.0 pM + 42.0 pM = 92.0 pM. HIn- has an absorbance maximum at 434 nm and In2 has a maximum at 620 nm. The sensor measures the absorbance ratio RA = A620/A434 reproducibly without need for calibration. From this ratio, we can find C()2( [Pg.420]

W. W. Fowlis, Remote optical techniques for liquid flow and temperature measurement for Spacelab... 

Vaughan JM (2004) Remote optical sensing and measurement. In Dakin J and Brown R (eds.) Elandbook of Optoelectronics. Bristol lOP Publishing. 

J.S. McCormack Remote optical measurements of temperature using fluorescent materials. Electr. Lett. 17, 630 (1981)... 

H Owen, JM Tedesco, JB Slater. Remote optical measurement probe. U.S. Patent 5,377,004 (filed October 15, 1993 issued December 27, 1994). 

Usually on-line IR spectroscopy is used to monitor the chemical evolution under UV irradiation of fast curable resins as thin films. Baillet et al. [190] proposed remote optical-fibre Raman spectroscopy equipped with an He-Ne 633 nm laser that allows... 

BE-7S67 Fibre optics for remote monitoring of structural integrity of elevated temperature insulated systems (FORMS) Mr. Manuel Gomea Eitrada Nacional... 

The sample cells for molecular fluorescence are similar to those for optical molecular absorption. Remote sensing with fiber-optic probes (see Figure 10.30) also can be adapted for use with either a fluorometer or spectrofluorometer. An analyte that is fluorescent can be monitored directly. For analytes that are not fluorescent, a suitable fluorescent probe molecule can be incorporated into the tip of the fiber-optic probe. The analyte s reaction with the probe molecule leads to an increase or decrease in fluorescence. 

Fiber-Optic Probes. Fiber-optic probes provide remote sampling capabilities to Raman instmmentation, are stable, and give reproducible signals. Their historical niche has been in environmental monitoring. More recently these probes have been used in chemical process control and related areas such as incoming materials inspection. 

For the visible and near-ultraviolet portions of the spectmm, tunable dye lasers have commonly been used as the light source, although they are being replaced in many appHcation by tunable soHd-state lasers, eg, titanium-doped sapphire. Optical parametric oscillators are also developing as useful spectroscopic sources. In the infrared, tunable laser semiconductor diodes have been employed. The tunable diode lasers which contain lead salts have been employed for remote monitoring of poUutant species. Needs for infrared spectroscopy provide an impetus for continued development of tunable infrared lasers (see Infrared technology and RAMAN spectroscopy). 

The objective ia any analytical procedure is to determine the composition of the sample (speciation) and the amounts of different species present (quantification). Spectroscopic techniques can both identify and quantify ia a single measurement. A wide range of compounds can be detected with high specificity, even ia multicomponent mixtures. Many spectroscopic methods are noninvasive, involving no sample collection, pretreatment, or contamination (see Nondestructive evaluation). Because only optical access to the sample is needed, instmments can be remotely situated for environmental and process monitoring (see Analytical METHODS Process control). Spectroscopy provides rapid real-time results, and is easily adaptable to continuous long-term monitoring. Spectra also carry information on sample conditions such as temperature and pressure. 

Hereia optical spectroscopy for laboratory analysis, giving some attention to remote sensing usiag either active laser-based systems (13—16) or passive (radiometric) techniques (17—20), is emphasized. 

Radiometry. Radiometry is the measurement of radiant electromagnetic energy (17,18,134), considered herein to be the direct detection and spectroscopic analysis of ambient thermal emission, as distinguished from techniques in which the sample is actively probed. At any temperature above absolute zero, some molecules are in thermally populated excited levels, and transitions from these to the ground state radiate energy at characteristic frequencies. Erom Wien s displacement law, T = 2898 //m-K, the emission maximum at 300 K is near 10 fim in the mid-ir. This radiation occurs at just the energies of molecular rovibrational transitions, so thermal emission carries much the same information as an ir absorption spectmm. Detection of the emissions of remote thermal sources is the ultimate passive and noninvasive technique, requiring not even an optical probe of the sampled volume. 

List the advantages and disadvantages of remote sensing techniques by optical methods. 

A Similar aphical presentation of the spatial distribution of a tracer g is or a real contaminant and thereby to some extent the airflow in the studied area is based on the use of computed tomography and optical remote sens-jt]g I2.M beams are sent out horizontally and reflected back to an IR analytical instrument, analyzing the average concentration of the contaminant along the IR beam. By combining data from several measured tines it is possible ro present data in a similar way to Fig. 12.8. Those methods presuppose access ro an expensive and complicated sampling/data processing system. 

In certain cases, the optical probe can be used at a large distance from the experimental equipment. Hence, spatial zones can be probed that are normally accessible with difficulty or inaccessible for traditional measurement devices. This arrangement provides a means for remote measurements. 

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