Apparatus and method for monitoring particle flow in a stack

Apparatus for monitoring particles flowing in a stack, the apparatus comprising:

• a light source for emitting light along an optical path for scattering from the particles;
• a rotatable monitoring assembly mounted in the optical path;
• a detector for detecting the scattered light;
• wherein the rotatable monitoring assembly contains at least two apertures and is configurable into a plurality of different configurations, including:
• an operation configuration, wherein the light passes through the rotatable monitoring assembly and into the stack unimpeded;
• a zero-check configuration, wherein the rotatable monitoring assembly blocks the light from reaching the stack;
• a span-check configuration, wherein light of varying intensity passes from the light source through the rotatable monitoring assembly into the stack;
• a contamination-check configuration, wherein the light is reflected through the rotatable monitoring assembly onto the detector, without entering the stack;
• and
• a safety-shutter configuration, wherein the rotatable monitoring assembly protects the detector from the particles in the stack,
• wherein the rotatable monitoring assembly is positioned along an optical axis of the light source, and is rotatable about an axis parallel to the optical axis of the light source.

An apparatus for monitoring particles flowing in a stack, the apparatus comprising:

• a light source for emitting light along an optical path for scattering from the particles;
• a rotatable monitoring assembly mounted in the optical path;
• a detector for detecting the scattered light;
• wherein the rotatable monitoring assembly contains at least two apertures and is configurable into a plurality of different configurations, including:
• an operation configuration, wherein the light passes through the rotatable monitoring assembly and into the stack unimpeded;
• a zero-check configuration, wherein the rotatable monitoring assembly blocks the light from reaching the stack;
• a span-check configuration, wherein light of varying intensity passes from the light source through the rotatable monitoring assembly into the stack;
• a contamination-check configuration, wherein the light is reflected through the rotatable monitoring assembly onto the detector, without entering the stack;
• and
• a safety-shutter configuration, wherein the rotatable monitoring assembly protects the detector from the particles in the stack, wherein the rotatable monitoring assembly includes a third aperture for allowing light to pass from the light source to the stack.