Analysis of errors of coal quality monitors

On-line nuclear meters have been in use in the coal industry for many years. They have been utilised for coal quality monitoring, in the control systems for coal blending, or for separating coals in the heavy media separation process. Their operation is based on the scattering or the absorption of incident gamma radiation, and the derived density or ash value is the result of a time-averaged measurement. In this paper, errors of ash monitors have been analysed. These errors appear due to several reasons: measurements are performed on samples which inaccurately represent a whole mass of tested coal, measuring methods are sensitive to variations in chemical composition of ash, size distribution of coal and moisture content. The signal from the radiation detector has to be averaged over a long period of time which results in delay of measuring results.