Design and Implementation of ZPW-2000 Frequency Shift Signal Coding and Detection Instrument

A signal detection experimental equipment using the ZPW-2000 frequency shift signal detection method is designed, which is based on the cycle frequency measurement method. The experimental track circuit frequency shift signal detection apparatus has an field programmable gate array（FPGA） at its core. The side frequency detection method uses two counters to detect the upper and lower jumping edges of the counting signal, and the counting error is reduced to 0-1 counting signal cycle by choosing the larger value of the two sets of counting values. The side frequency detection error can be controlled within 0.07 Hz under the counting signal of 200 MHz. The detection method uses eight counters to realize the detection of shifted frequency information. In order to achieve the acquisition of low-frequency components in the frequency-shifted signal as well as the detection and calculation of low-frequency frequency, the low-frequency detection employs six asynchronous counters, respectively. The experimental instrument measurement demonstrates that the side frequency and low-frequency detection error can meet the requirements of the railway standard TB/T 3532—2018 in the frequency shifted signal up and down the side frequency error of ±0.15 Hz and low-frequency error of ±0.03 Hz. The experimental instrument can accurately calculate the shifted frequency information, which is based on the FPGA ZPW-2000 frequency shifted signal generator. The experimental equipment breaks the limitations of specialized equipment in teaching and experiment, and help students better understand how track circuits are coded and detected.