Sensing pulverized material mixture proportions by resonant cavity measurements

Based on differences in the permittivity of coal and limestone rock, a resonant cavity measurement technique is presented for the rapid determination of the proportions of coal and limestone in powdered mixtures. The ratio of the resonant frequency shift and the change in the transmission factor when mixed coal and limestone samples are inserted into the cavity provides a means for estimating the percentage of coal in the mixture relatively independent of the bulk density of the mixture. The technique might be developed for rapid tests of dust in coal mines to determine whether the 65% noncombustible content requirement is being met for prevention of coal mine explosions.