Apparatus and method for monitoring particle flow in a stack

Abstract

A method and apparatus () 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 () mounted in the optical path, and detecting the scattered light using a detector. The rotatable monitoring assembly () contains at least two in apertures, and the method further comprises rotating the rotatable monitoring assembly () into a plurality of different configurations. In an operation configuration, light passes through the rotatable monitoring assembly () and into the stack unimpeded. In a zero-check configuration, the rotatable monitoring assembly () 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 () into the stack. In a contamination-check configuration, the light is reflected through the rotatable monitoring assembly () onto the detector, without entering the stack. In the safety-shutter configuration, the rotatable monitoring assembly () protects optical components in the instrument from particles in the stack.