Underground electromagnetic measure and filter based on time-frequency analysis applied in coal mine monitoring system

Because all equipments run in the underground explosive atmosphere, the underground electromagnetic measurement could not be accomplished perfectly. A novel electromagnetic soft-sensing method was proposed to measure the electromagnetic distribution indirectly. The wavelet time-frequency analysis was introduced to monitoring system and the electromagnetic interference(EMI) sources could be ascertained. The startup time, duration and waveform could be detected based on the running records of underground electric equipments. It is seen that it is convenient to perform the EMI measurements while the total cost can be reduced greatly. Moreover, the electrical surge, the most outstanding interference, was studied to verify the validity of wavelet analysis. EMI filter was improved in accordance of the EMI gotten from wavelet analysis. Power port immunity was developed obviously. Therefore the surge of data port was restrained markedly with wavelet filtration and the protection circuit. Coordinative effect of EMI power and wavelet filter resulted in reduction of sensor false alarms. Results indicate that wavelet analysis and the improved EMI filter have enhanced the electromagnetic compatibility(EMC) of monitoring substations and sensors obviously. It is concluded the wavelet analysis is of guiding significance to measure underground EMI distribution and improve EMC of the underground monitoring system.