Abstract: A method and apparatus (1) for monitoring particles flowing in a stack are disclosed. The method comprises emitting light from a light source along an optical path for scattering from the particles, rotating a rotatable monitoring assembly (15) mounted in the optical path, and detecting the scattered light using a detector. The rotatable monitoring assembly (15) contains at least two in apertures, and the method further comprises rotating the rotatable monitoring assembly (15) into a plurality of different configurations. In an operation configuration, light passes through the rotatable monitoring assembly (15) and into the stack unimpeded. In a zero-check configuration, the rotatable monitoring assembly (15) blocks the light from reaching the stack. In a span-check configuration, light of varying intensity passes from the light source through the rotatable monitoring assembly (15) into the stack.

Abstract: A method and apparatus (1) for monitoring particles flowing in a stack are disclosed. The method comprises emitting light from a light source along an optical path for scattering from the particles, rotating a rotatable monitoring assembly (15) mounted in the optical path, and detecting the scattered light using a detector. The rotatable monitoring assembly (15) contains at least two in apertures, and the method further comprises rotating the rotatable monitoring assembly (15) into a plurality of different configurations. In an operation configuration, light passes through the rotatable monitoring assembly (15) and into the stack unimpeded. In a zero-check configuration, the rotatable monitoring assembly (15) blocks the light from reaching the stack. In a span-check configuration, light of varying intensity passes from the light source through the rotatable monitoring assembly (15) into the stack.

Abstract: A method of monitoring particles in a stack comprises generating on a first side of the stack a beam of light directed towards a second, opposite, side of the stack. The beam is reflected back towards the first side of the stack and through the particles in the stack. An image is obtained of light scattered from the particles. The image is obtained using an imager positioned and oriented to have a field of view that includes unwanted scattered light. The method includes the step of blocking the unwanted scattered light from the image.

Abstract: A method of monitoring particles in a stack comprises generating on a first side of the stack a beam of light directed towards a second, opposite, side of the stack. The beam is reflected back towards the first side of the stack and through the particles in the stack. An image is obtained of light scattered from the particles. The image is obtained using an imager positioned and oriented to have a field of view that includes unwanted scattered light. The method includes the step of blocking the unwanted scattered light from the image.