The rail length measurement circuit design based on the lock-in amplifier technology

The paper studied the rail length measurement method, analyzed the sound waves attenuation in rails. The sound wave attenuated severely after traveling through the rail, so adopted the signal correlation principle of the lock-in amplifier to detect weak signal. Then completed the circuit design such as the acoustic emission circuit, the preamplifier circuit, the signal operation circuit of the digital lock-in amplifier and so on. The lock-in amplifier did correlation operation between the signals and completed the reference signal phase shift function by DSP and at last, detected the weak signals in noises.