Device for measuring the opacity of smokes

Claim 1

In a device for measuring the opacity of gases by absorption of a luminous beam through which said gases are passed, said device including: a. an optical system having a light source, a condenser system and a diaphragm arranged to pass a luminous beam first to a semi-reflecting mirror and then along a first path to a reflecting mirror from which said luminous beam is reflected back along said first path to said semi-reflecting mirror and is reflected along a second path onto a photo-element; and b. an outlet chamber having a Venturi tube positioned orthogonally to said first path for passing gases through said luminous beam of said optical system, said Venturi tube having its narrowest section coincident with said first path, the improvement which includes a Venturi which in its narrow section is not less than 100 mm in diameter, said semireflecting mirror being inclined relative to said luminous beam and at an angle of about 45*, an infra-red filter located in front of said photoelement along said second path and support means for suspending said device for measuring the opAcity of gases on said first path of said luminous beam.