Analog optical rock dust meter

The US Bureau of Mines previously constructed a portable meter based on optical reflectivity for measuring the concentration of rock dust in rock dust-coal dust mixtures. This early design was accurate to within +or-2 wt.% rock dust for mixtures whose rock dust concentration was between 30 wt.% and 100 wt.%. Below 30 wt.% rock dust, the meter exhibited poor accuracy. The Bureau researchers have redesigned the meter based on a theory for optical reflectivity of binary dust mixtures. This new meter was tested against both laboratory-prepared coal-dust-rock-dust mixtures and samples taken from various coal mines and found to be accurate to +or-2-wt.% rock dust from 0 wt.% to 100 wt.%. The meter also has a lower power consumption than the previous model (which translates into longer battery life between charges), has fewer internal and external adjustments, is lighter in weight and can be held comfortably in one hand. It can be readily field calibrated.<>