ABSTRACT

For industrial applications, a notable exception is nitrogen, which being homonuclear, has only negligibly weak absorption, and being chemically rather inert, exhibits minimal interaction with chemical indicators. It is unfortunate that even the most cost-efficient optical sensors are still often several times more expensive than other sensor types. Industrial markets are highly sensitive to cost. It is therefore important to emphasize the other attractions of optical methods. Direct optical detection of gases offers the potential for a rapid, almost instantaneous response, typically determined by the integration time constant of detectors needed to provide a good signal-to-noise ratio. This allows leaks or pollution to be detected more rapidly than with many other sensor types and helps in rapid determination of the dynamics of processes such as combustion. The characteristic wavelengths at which the gas absorbs can often be used to identify the gas species.