Double pass opacity monitor for monitoring opacity and smoke emissions

The DSL-320 Opacity Monitor is an optical instrument designed to measure the visible opacity of exhaust gas in a duct, stack or flue.


Gas flow's measurement
In situ measurement directly in exhaust gas flow
Opacity's measurement
Measurement reading as % Opacity
Modulated green LED source
Modulated green LED source for long lifetime stability and immunity to ambient light
Rugged construction
Rugged 316 stainless steel construction
In-situ zero and calibration check facility
Interface options
Choice of interface options enabling easy integration
Free utility software
Free utility software for PC based set-up, control and data logging
Optional Operator Interface
Optional Operator Interface with different mounting configurations

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The DSL-320 uses the double pass light transmission measurement technique, with a folded beam Transceiver/Reflector arrangement. A light beam emitted from the Transceiver (TRX) passes across the duct, stack or flue to a Reflector, which then returns the light to the Transceiver where the intensity of the received light is measured.

Increased particulate or smoke density in the stack gas attenuates the transmitted light and causes the intensity of the received light to fall. This reduction in intensity is measured and presented as % opacity. The higher the level of particulate or smoke present, the more light lost and therefore, the greater the opacity.


  • Simpler installation than single pass opacity monitors
  • Better accuracy over shorter path lengths than single pass opacity monitors
  • Rugged design with no moving parts so low maintenance
  • Latched head and lid design to enable ease of access for installation and maintenance

Why do you need DSL-320 ?

Ideal for monitoring opacity and smoke levels in the exhaust gas of industrial combustion or air filtration processes.

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