OPAL SINGAPORE
Environmental Systems
Lambert-Beer law
When a monochromatic light beam traverses through gas containing particulate matter and color, the intensity of the beam will decrease by absorption and scattering processes within the particulate distribution. The net effect is described by the Lambert-Beer law.
Transmissometer
Transmissometer, also termed opacity monitor, measure the transmittance of light that passes through a flue gas.
Continuous Emission
Monitoring System
 | | The optical system in a transmissometer is designed to captured the ratio of both intensities I / Io is the fractional transmittance. The opacity which is the primary output of the instrument is calculated through the following expression: Opacity = 1.0 - Transmittance Opacity can be defined as "the fraction of incident light that is attenuated by an optical medium of interest" (US EPA 40 CFR 60, Appendix B). |
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NON-DISPERSIVE INFRARED
An infrared source generates broad band radiation which is modulated by a mechanical chopper. This energy is transmitted through a sample cell to the detector. The detector comprises two or three series of arranged chambers, filled with the gas to be measured and a small flow path between the chambers, incorporating the microflow sensor. An infrared pulse reaching the front chamber heats the gas due to specific absorption, causing expansion and flow from front chamber to back chamber. The change in flow amplitude is related to the gas concentration in the sample cell. The signal from the detector is fed into the microcontroller. 