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Opacity The amount of light obscured by particulate pollution in the air; clear window glass has zero opacity, a brick wall is 100 percent opaque. Opacity is an indicator of changes in performance of particulate control systems.

Public awareness of environmental pollution, especially the release of toxic pollutants, is increasing. Continuous monitoring systems are used to provide assurance that a facility is not emitting pollutants in excess of its standards.

The application of continuous monitoring systems serve many purposes including:
Compliance monitoring
Εnforcement and public relations tool to address public concerns over stack emissions

Modern methods for opacity measurement still use the darkness of the stack gases to measure the amount of smoke or dust emitted within the exhaust gases.
Our opacity monitors use the light transmission technique to measure the visible opacity of exhaust gas in a duct, stack or flue, in which a high intensity light beam is projected across the stack. Any dust, smoke or particulate present will attenuate the transmitted light and the decrease in light intensity, due to absorption and scattering, is measured.

One advantage of opacity systems is that they are insensitive to interference from other flue gas components since the beam spectrum is within the photopic region (400-700 nm) and most other flue gas constituents do not absorb in this spectral region.

There are two types of opacity monitors; Single Pass and Double Pass.

Single pass opacity monitors have a Transmitter/Receiver arrangement with the light beam emitted from the Transmitter passing across the stack to a Receiver. Double pass opacity monitors have a folded beam Transceiver/Reflector arrangement with the light beam emitted from the Transceiver (TRX) passing across the duct to a Reflector, which then returns the light to the Transceiver.

Single pass opacity monitors are the simplest type of instrument and offer a very cost effective solution to meet monitoring requirements. One advantage to single pass systems is that they are suitable for applications with long path lengths, i.e. large stack diameters and our single pass opacity monitors can be used for path lengths of up to 20m.

Double pass systems are more suited to continuous emission monitoring as they have a number of advantages over single pass systems in that:

Double pass opacity monitors have better sensitivity at smaller duct diameters
Double pass opacity monitors are simpler to install as electrical services are only required to one side of the stack

Double pass opacity monitors allow for an in-situ zero and calibration facility

We currently offer three different opacity monitors.

220 Series Single Pass Opacity Monitor

320 Series Double Pass Opacity Monitor

460 Series Double Pass Opacity and Particulate Monitor


Series output as particulate (mg/m3) output as opacity (%) Measurement Technique Cal Check Option Single Pass Double Pass Compliance
220 Light Transmission Manually CE
320 Light Transmission Manually CE
460 Light Transmission Manually CE