The methods of measuring dust content in flue gas are specified by Japanese Industrial Standard (JIS Z-8808). A standard method is the dust tube and filter paper method. This is based on manual gravimetric procedures which make continuous measurement impossible. A continuous monitor, therefore, is required for controlling the operating conditions of boilers and dust collectors.
On line measuring of dust concentration can be achieved by light schattering, light transmittance and quantity of electrostatic charge. In United States, opacity is introduced to evaluate dust emission from stationary sources, is relative to the light transmittance.