Design of Signal Processing System for Pipeline Pig Tracking and Positioning Receiver Based on Orthogonal Digital Lock-in Amplification Principle

The current signal processing system of pipeline pig tracking and positioning receiver based on bandpass filter is difficult to ensure high reliability and sensitivity when receiving weak signals from transmitters in complex environments due to limitations of Q value. Meanwhile, the frequency characteristics and overall sensitivity of the signal processing stages within the system are fixed and not adjustable, limiting the system's ability to adapt to different operating modes under varying environmental conditions. This paper presents a signal processing system based on orthogonal digital lock-in amplification principle. The system employs operational amplifier AD821 with low-noise for preamplification, specialized filter chips LTC10696 and LTC1068200 with adjustable frequency characteristics for low-pass filtering and band-pass filtering, then STM32F103RBT6 microcontroller is utilized to perform the A/D conversion and orthogonal digital lockin amplification (DLIA) processing. The system can reliably receive the 23 Hz sinusoidal signal from the transmitter with ultrahigh sensitivity, and its frequency characteristic and receiving sensitivity can be flexibly adjusted through programming. Experiment shows that the system can meet the diversified demands for detection sensitivity under different environmental conditions, with effective receiving sensitivity (up to 40 m in the highest sensitivity setting) much higher than current systems (less than 20 m).