针对同忻煤矿在线监测井下毛煤灰分的应用需求，基于灰分与煤的天然放射性呈正相关的原理，通过采用高射线透过率材料的隔爆型矿用射线探测器、由隔离变压器供电的光纤通讯分析仪表以及由内外屏蔽实现低本底水平的环境屏蔽体，完成了井下矿用无源灰分仪的设计，并将之应用于同忻煤矿井下毛煤的灰分监测。实践表明：矿用无源灰分仪应用效果良好，测量值与人工化验值的均方根误差低于1.26%；利用灰分监测数据指导井下采煤生产，使毛煤年平均灰分下降了0.76个百分点，达到了从源头加强煤质管控的目的。

In order to meet the needs of Tongxin Mine for online monitoring of ash of run-of-mine coal underground, a mine passive ash meter is developed and put into service. The ash meter is designed based on the principle that coal ash is directly, correlated with natural radioactivity, and through the use of flameproof γ-ray detector made materials featuring a high radiation transmittance, the optical fiber communication analysis device powered by shielded transformer, and the both internally and externally shielded cost-effective environmental screening structure. Practice shows that the meter works remarkably well; compared with the analytical value, the root-mean-square error of the measured value is smaller than 1.26%; and with the use of the measured data to direct mining operations, the ash of run-of-min coal is seen to be decreased by 0.76 percentage points on an average annual basis. The use of the ash meter has attained the objective of strengthening coal quality control at the source.