Spectroscopy is a branch of physics which is concerned with the production, measurement, and interpretation of electromagnetic spectra arising from either emission or absorption of radiant energy by various substances. Essentially, a beam of polychromatic light is directed to a sample. The light transmitted through the sample, reflected from the sample, or both is then collected and analyzed. Analysis involves separating the collected light into its individual wavelengths and then determining the energy content at each wavelength. Because a sample will absorb certain wavelengths of light more than others, the collected light has a spectrum which is indicative of the composition of the sample.
Because spectroscopy can rapidly provide accurate composition analysis, it has found a wide variety of applications. For example, in the areas of food and agriculture, spectrometers are used for the measurements of constituents in dairy products, cereal, grains, beverages, fruits, meats, etc. Other examples of applications for spectroscopic analyzers include:
measuring lubrication of yarn and for fiber finish in nylon, polyester, cotton and others in the textile industry; PA1 measuring the percent of tar and nicotine in the tobacco industry; PA1 chemical analysis of paper including colorings, thickness, and moisture in the paper industry; PA1 measuring tape and film thicknesses in the plastics industry; PA1 compositions determination in the gasohol and petroleum industry; PA1 measurement of the content of oils and other ingredients in the cosmetics and perfume industry; and PA1 measurement and identification of drug composition in the pharmaceutical industry.
There are various types of spectral analyzers on the market for performing these types of analysis, including the moving grating analyzer and the fixed grating, detector array-type analyzer. The moving grating analyzer provides highly accurate spectral data and is best suited for applications where accuracy is paramount. These devices are capable of scan/sample rates up to a few scans per second. U.S. Pat. No. 4,540,282 to Landa et al. discloses one such scanning analyzer.
For applications (e.g., product sorting) where speed is paramount, the fixed grating, detector array-type analyzer is most suitable. Fixed grating analyzers are capable of scan rates in excess of 100 scans per second. The conventional fixed grating analyzers includes a light source, an optical probe or a sample chamber, and a spectrograph. The analyzer is normally a single channel device. That is, only a single probe is used such that the analyzer can only be used for a single application at any one time.
Because spectral analyzers tend to be expensive, it is desirable to produce a multiple channel analyzer. Multiple channels would allow a single analyzer to be simultaneously used for numerous measurements and applications. In order to handle multiple channels, the analyzer must time multiplex the spectral data which is provided to the spectrograph. Unfortunately, conventional optical multiplexing schemes have tended to be inaccurate and slow such that the very forte of the analyzer is sacrificed for the added channels.