Development of a miner personal dust continuous monitor based on the principle of oscillating balance

Abstract

An accurate measurement of coal mine dust concentration is an important prerequisite for effective dust control. Traditional offline filter sampling gravimetric methods need a long measuring period and cumbersome operations, while direct-reading light absorption/scattering measurement methods are susceptible to environmental conditions and dust properties. To overcome the above-mentioned problems, a miner personal dust continuous monitor based on the principle of oscillating balance was developed. The finite element simulation method was used to explore the effects of different characteristics of the oscillating element on the response frequency and mass sensitivity of the oscillation system. The optimal gradient optimization algorithm was used to design the material and shape of the oscillating element. An oscillating tube with highly stable elastic modulus was fabricated. Its frequency temperature coefficient is 3×10−5 Hz/℃, which is minimally affected by temperature, ensuring the accurate measurement of the oscillation frequency when the external ambient temperature conditions vary. An oscillating balance mass sensor was developed. A digital self-excited oscillation closed-loop control circuit was designed to realize the automatic control of resonant frequency and real-time output. The oscillating balance mass sensor had a mass sensitivity of approximately 1 mg/Hz and a mass detection limit of 2 μg. Finally, a miner personal dust continuous monitor based on the principle of oscillating balance was developed for the first time in China by integrating the respiratory dust sampler, the total dust sampler, the heating tube, the mass sensor, the air pump, the flow rate controller, and the temperature, humidity and pressure sensors. The detection limit of this instrument is 0.035 mg/m3 in terms of the average dust mass concentration. The instrument can provide continuous monitoring information, including the real-time total dust or respirable dust concentration and the cumulative occupational exposure concentration of the day. This instrument was applied to dust measurement in an underground coal mine. Its measurement results were compared with those from the instrument using traditional filter sampling gravimetric method, with a relative error of approximately 5%. This instrument has the capability of rapid and accurate measurement of coal mine dust. It has the potential to be an alternative of offline filter sampling weighing methods and direct-reading dust monitors based on optical principles.

Keywords

• coal mine dust
• oscillating balance
• mass sensing
• dust monitor