Microprocessor-controlled spectrometers are available to measure concentrations of a variety of gases and vapors in ambient air. These units can be portable or permanently installed and can comply with environmental and occupational safety regulations. In the IR spectrometer design, an integral air pump draws ambient air into the test cell, operating at a flow rate of 0.88 acfm (25 l/min). The microprocessor selects the wavelengths for the components and the filter wheel in the analyzer allows the selected wavelengths to pass through the ambient air sample in the cell. The microprocessor automatically adjusts the path length through the cell to give the required sensitivity. Because of the folded-path-length design, the path length can be increased to 20 m (60 ft), and the resulting measurement sensitivity is better than 1 ppm in many cases.
As shown in Table 5.10.2, practically all organic and some inorganic vapors and gases can be monitored by these IR spectrometers. The advantage of the microprocessor-based operation is that the monitor is precalibrated for the analysis of over 100 Occupational Safety and Health Administration (OSHA)-cited compounds. The memory capacity of the microprocessor is sufficient to accommodate another ten user-selected and user-calibrated gases. Analysis time is minimized because the microprocessor automatically sets the measurement wavelengths and parameters for any compound in its memory. A general scan for a contaminant in the atmosphere takes about 5 min, while the analysis of a specific compound can be completed in just a few minutes. The portable units are battery-operated for 4 hr of continuous operation and are approved for use in hazardous areas.
Was this article helpful?