Filter photometer, infrared

Instrument Designs for Infrared Absorption The simplest instrument for IR absorption spectroscopy is a filter photometer similar to that shown in Figure 10.24 for UV/Vis absorption. These instruments have the advantage of portability and typically are used as dedicated analyzers for gases such as ITCN and CO. 

The dispersive infrared analyzer, which is similar to the double-beam spectrometer, is capable of analyzing components of liquid and gaseous process streams. In contrast, the nondispersive infrared analyzer, which is a filter photometer, is more suited to the selective analysis of components of gaseous process streams. In general, the design and operation of nondispersive infrared analyzers are simpler than those of dispersive infrared analyzers. Also, the use of filtering techniques with the nondispersive infrared analyzers increases the selectivity of the analysis, but this can also reduce sensitivity. These infrared analyzers are commonly used for the analysis of... 

We use the term colorimeter to designate an instrument for absorption measurements in which the human eye serves as the detector using one or more color-comparison standards. A photometer consists of a source, a filler, and a photoelectric transducer as well as a signal processor and readout. Note that some scientists and instrument manufacturers refer to photometers as colorimeters or photoelectric colorimeters. Filter photometers are commercially available for absorption measurements in the ultraviolet, visible, and infrared regions, as well as emission and fluorescence in the first two wavelength regions. Photometers designed for fluorescence measurements arc also called fluorometers. 

Infrared (IR) spectroscopy offers many unique advantages for measurements within an industrial environment, whether they are for environmental or for production-based applications. Historically, the technique has been used for a broad range of applications ranging from the composition of gas and/or liquid mixtures to the analysis of trace components for gas purity or environmental analysis. The instrumentation used ranges in complexity from simple filter-based photometers to optomechanically complicated devices, such as Fourier transform infrared (FTIR) spectrometers. Simple nondispersive infrared (NDIR) insttuments are in common use for measurements that feature well-defined methods of analysis, such as the analysis of combustion gases for carbon oxides and hydrocarbons. For more complex measurements it is normally necessary to obtain a greater amount of spectral information, and so either Ml-spectrum or multiple wavelength analyzers are required. 

Infrared photometers designed to monitor the concentration of air pollutants, such as carbon monoxide, nitrobenzene, vinyl chloride, hydrogen cyanide, and pyridine, are often used to ensure compliance with regulations established by the Occupational Safety and Health Administration (OSHA). Interference filters, each designed for the determination of a specific pollutant, are available. These transmit narrow bands of radiation in the range of 3 to 14 p,m. 

Flame infrared emission (FIRE) spectrometry is a new technique that is useful in determining FAC in liquid bleach. In the FIRE method, solutions of sodium hypochlorite are acidified to produce aqueous CI2 (reactions [I] and [II] and Figure 1). Dissolved CI2 is liberated from solution in a purge tube and converted to vibrationally excited HCl molecules in a hydrogen-air flame. The intensity of the P-branch of the HCl stretching vibration at 3.8 pm is monitored with a simple filter infrared photometer that employs a lead selenide detector. 

The definition team for the infrared photometer consists of R. Hall, D. Kleinmann and G. Neugebauer. As a first generation experiment the team proposes a simple filter wheel photometer which works from 1 p to 1 mm. A spectrometer with a spectral resolution of 3 x 10 is proposed for a second generation... 

Figure 2 - One concept of the infrared radiometer layout is shown. The photometer contains a dewar with a one-year lifetime, the chopper for removing the background offset, two detectors and a set of variable apertures and filters for each.

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