Optical process control

Chemical Gas Detection. Spectral identification of gases in industrial processing and atmospheric contamination is becoming an important tool for process control and monitoring of air quaUty. The present optical method uses the ftir (Fourier transform infrared) interference spectrometer having high resolution (<1 cm ) capabiUty and excellent sensitivity (few ppb) with the use of cooled MCT (mercury—cadmium—teUuride) (2) detectors. 

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. 

The development of fiber optics technology, user-friendly displays, and enhanced data presentation capabihties have made on-line analysis acceptable within the plant manufactuting environment. However, it is apparent that a barrier stiU exists to some extent within many organizations between the process control engineers, the plant operations department, and the analytical function, and proper sampling is stiU the key to successful process analytical chemistry. The ultimate goal is not to handle the sample at ah. 

Phototypesetting represented an easier way to compose type. Eady phototypesetters used an optical process, whereby a disk of characters, ia different sizes and typefaces, was spun under computer control. Each character was projected ia turn onto photosensitive film or paper. This was followed by systems where characters drawn on a cathode ray tube (CRT) exposed the photosensitive material. In each case, the operator iateracted with the system at a video screen that only showed the characters of the text (the iaformation content) and codes that iadicated how the characters were to look on paper. An experienced operator was required to obtain high quaUty results. 

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. 

Abbott, M. Roth R.J. Henry, Automated Process Control of Moisture II — Optical Moisture Analyzer , PATR 4298 (1971)... 

Miller H.H., Hirschfeld T.B., Fiber optic chemical sensors for industrial and process control, Proc. SPIE-Int. Soc. Opt. Eng. 1987 718 39. 

As a conclusion it has been demonstrated that optical sensors have a wide field of applications in the process control, surveillance and biosciences. They supply the chance to monitor processes an-line and with short time resolution. Interferometric sensors are rather sensitive and applicable in... 

A variety of optical oxygen sensor systems have been developed for applications such as biomedical, environmental and process control . But very few of them have been critically assessed for their suitability for food packaging applications. It has been proven that substantial development, optimization and redesign of the oxygen-sensitive materials and fabrication processes are required for the oxygen sensors to match practical requirements for these applications5. In particular, specific requirements of food applications are ... 

The manufacture of a photonic crystal requires extreme process control because a deviation from perfect periodicity in the order of a few percent of the wavelength worsens the optical performance. Macroporous silicon is a potential candidate for the realization of such structures because of its photolithographic patterning. The precision of the macroporous structures is reflected in the transmission measurements along the T-M and T-K directions, which exhibit a photonic band-gap centered at 5 pm, as shown in Fig. 10.16. For measurement the macroporous... 

C. Ovren, M. Adoleson, andB. Hok, Fibreopticsystems fortemperatureand vibration measurements in industrial applications, Proc. Int. Conf. Optical Techniques in Process Control, The Hague (1983). 

A. L. Harmer, Fibre optic sensors for offshore process control instrumentation, Proc. Optical Fibre Sensors Conference (OFS 86), Informal Workshop at Tusukuba Science City, 1986, VII. Pub Institute of Electronics and Communication Engineers of Japan, Tokyo, 1986. 

A.C. Quinn, P.J. Gemperline, B. Baker, M. Zhn, D.S. Walker, Eibre-optic UV/visible composition monitoring for process control of batch reactions, Chemom. Intell. Lab. Sysl, 45, 199-214 (1999). 

P. Kotidis, R. Crocrombe and W. Atia, Optical, tunable filter-based micro-instrumentation for industrial process control. Abstracts of Papers, Federation of Analytical Chemistry and Spectroscopy Societies (FACSS), Orlando, EL, USA, October 19-23, 2003, Federation of Analytical Chemistry and Spectroscopy Societies, Santa Fe, NM USA, 2002. 

This latter application is the key to the broadband femtosecond approach to nonlinear microspectroscopy presented here. From the point of view of coherent control, it becomes clear that high spectral bandwidths are needed providing a hnge nnmber of photon energies and, as such, interfering pathways is necessary to be able to achieve high interference contrast, and thus good controllability of optical processes. 

This CVD procedure is somewhat different from that used to deposit semiconductor layers. In the latter process, the primary reaction occurs on the substrate surface, following gas-phase decomposition (if necessary), transport, and adsorption. In the fiber optic process, the reaction takes place in the gas phase. As a result, the process is termed modified chemical vapor deposition (MCVD). The need for gas-phase particle synthesis is necessitated by the slow deposition rates of surface reactions. Early attempts to increase deposition rates of surface-controlled reactions resulted in gas-phase silica particles that acted as scattering centers in the deposited layers, leading to attenuation loss. With the MCVD process, the precursor gas flow rates are increased to nearly 10 times those used in traditional CVD processes, in order to produce Ge02-Si02 particles that collect on the tube wall and are vitrified (densified) by the torch flame. 

---