Induced polarization voltage signal detection of mine⁃used focused dual⁃frequency IP instrument based on phase⁃locked amplification technology

The underground environment of coal mines is harsh，the electromagnetic and noise interference in the ad⁃ vanced detection process in mine roadway is complicated，and the effective signal to be measured is weak and diffi⁃ cult to be accurately detected. To accurately detect the amplitude and phase of the weak IP signal，the double phase⁃ locked amplification technology is used to extract the signal under test from the noise signal. Based on the signal experiment test and the construction of the mine⁃focused dual⁃frequency instrument test platform，the noise suppres⁃ sion characteristics of the system under the interference of different noise signals are studied. The mathematical model of the dual phase⁃locked amplification technology has been established，and it is proved that the technology can be used for signal detection. The system’s suppression of even⁃numbered frequency⁃multiplied noise and odd⁃numbered frequency⁃multiplied noise have been theoretically analyzed. When the noise signal frequency is an odd multiple of the reference signal frequency，the relative error of the signal amplitude and phase increases with the increase of the ratio of the noise signal amplitude to the waiting signal amplitude. When the noise signal frequency is an even multiple of the reference signal frequency，the relative error of the signal amplitude and phase is independent of the noise signal amplitude，frequency and phase. Based on the above theoretical analysis，the test system is established based on the dual phase lock⁃in amplification technology，and the hardware circuit design and digital part processing algo⁃ rithm are provided. Also，the integration time characteristic and noise suppression characteristic test of the test system are completed. The results show that when the integration time is an integer multiple of the period of the signal to be measured， the DC noise and even⁃numbered frequency noise have basically no effect on the system， and the AC noise affects the calculated amplitude，while the effect on the calculated phase can be ignored. A prototype based on the phase⁃locked amplification technology is designed，and the test proves that the absolute value of measurement error of the voltage amplitude has nothing to do with the amplitude of the voltage signal，but has something to do with frequency. The prototype can collect the voltage signal with amplitude less than 5 V，and the absolute value of the maximum measurement error is less than 1.5%，which can realize the high⁃precision detection of the voltage signal amplitude and phase.