Guangdong Song

Advances of optical fiber sensors for coal mine safety monitoring applications

Optic fiber sensors (OFS) offer a number of unique advantages for safety monitoring in explosive and hazardous environment such as underground coal mines. This paper reports on latest development of fiber optic sensors for monitoring methane and other gases, detection of seismic events and application systems for hazard monitoring and early warning of coal mine combustion, roof integrity and seismic activities. The application potential and future trend of OFS research for coal mine hazard detection and prevention are also discussed in the paper.

A compact wideband precision impedance measurement system based on digital auto-balancing bridge

The ac impedance spectroscopy measurements are predominantly taken by using impedance analyzers based on analog auto-balancing bridge. However, those bench-top analyzers are generally complicated, bulky and expensive, thus limiting their usage in industrial field applications. This paper presents the development of a compact wideband precision measurement system based on digital auto-balancing bridge. The methods of digital auto-balancing bridge and digital lock-in amplifier are analyzed theoretically. The overall design and several key sections including null detector, direct digital synthesizer-based sampling clock, and digital control unit are introduced in detail. The results show that the system achieves a basic measurement accuracy of 0.05% with a frequency range of 20 Hz?2 MHz. The advantages of versatile measurement capacity, fast measurement speed, small size and low cost make it quite suitable for industrial field applications. It is demonstrated that this system is practical and effective by applying in determining the impedance-temperature characteristic of a motor starter PTC thermistor.

Sensitivity analysis and temperature performance of the fiber Bragg grating (FBG) acceleration sensor

A high sensitive fiber Bragg grating (FBG) acceleration sensor based on filtering demodulation is analyzed on sensitivity, resolution and temperature experiment. Sensitivity and resolution of FBG sensor lies on the structure of the sensor shell and the shape of the reflectivity spectrum of FBG. The temperature experiments of the FBG sensor show the work and storing temperature range of the sensor based on different preparing stress and packaging glue. Experiments on the detecting systems frequency character have been done. Results show that this acceleration sensor can detect the smallest acceleration of 1mm/s2 with a flat response from 5Hz to 40Hz.

Application of the fiber Bragg Grating (FBG) sensors in coal mines

The FBG strain sensors were applied to the Dongtan Mine to monitor the stress variation of the lined wall in the gateway retained along goaf of No. 3203 coal mining face on line. The results showed that the FBG strain sensor with high measuring range could measure the stress variation accurately during the support process of the gateway retained along goaf and could provide the basis to further optimize the support structure and to determine the support plan of the gateway retained along the goaf. The FBG micro-seismic sensors were used in Xinglong Mine to detect micro-seismic signal. The signals are well received and analyzed to determine the earthquake source and do warming. The FBG sensors and detecting system show great prospect in micro-seismic detection, and geological disasters detecting.

Distributed fiber optic microseismic monitoring system for coal mines

Microseismic monitoring is essential for rock burst predication in coal mines. However, the existing monitoring instruments based on electric geophone have inherent limitations and hardly progress further. This paper presents the design and implementation of a novel microseismic monitoring system using fiber optic sensing and distributed data acquisition techniques. The technical details including seismic sensor, interrogation system, and seismic substation are introduced. The results show that the system achieves a bandwidth of 0.5-400 Hz and a dynamic range of 80 dB. The location accuracy reaches 10 m by reasonable configuration of sensors, and so it is particularly suitable for precision mine microseismic monitoring.

Research on microseismic energy calculation and duration automatically picking

Accurate measurement of energy is a technical difficulty that various microseismic monitoring systems are facing. In this article, we applied the groundbreaking fiber optics microseismic monitoring system to mine rock burst monitoring for the first time around the world. We suggest to calculate microseismic energy via the duration of vibration. Precise picking of P wave first arrival and end point is essential to microseismic energy calculation. According to the huge energy difference before and after the arrival of the seismic wave, we use the sliding time-window energy ratio method to pick the first arrival and end point, and put forward the quantitative relationship between the sliding time-window width TWL and the sampling frequency as well as the signal dominant frequency for the first time. The results of P wave automatically picking are almost the same as those manually picked. However the end point may need to be corrected if wave distortion occurred.

A high sensitive fiber Bragg grating(FBG) geophone detecting system

A high sensitive fiber Bragg grating (FBG) geophone detecting system based on narrow line width distributed feedback (DFB) laser is realized by using filtering demodulation. Sensitivity of FBG geophone lies on the structure of the sensor shell and the shape of the reflectivity spectrum of FBG. Experiments on the detecting systems frequency character have been done. Results show that this geophone can detect the smallest acceleration of 1mm/s2 with a flat response from 5Hz to 40Hz.. The experiments on coal mine exhibit that the geophone can be used to measure microseismic signals. The detecting system shows great prospect in micro-seismic detection, and geological disasters detecting.