Interference Fringes and Time Interval Measurement Method for Gravimeter Based on Dual Phase-Locked Loop IP Core in FPGA

The principle and method of measuring falling time and distance of the falling body in the absolute gravimeter by FPGA are introduced, and the programmable system-on-chip based on Altera Cyclone IV series EP4CE6E22C8N chip and the implementation process of frequency doubling phase shift timing method are described. The measurement error of the falling body in the gravimeter during a falling process of about 200m is ± 0.6ns. The standard uncertainty of measurement is 0.308ns, and the resolution can reach 0.4ns, which improves the accuracy of the existing absolute gravimeter. Finally, the correctness and effectiveness of the design are verified by simulation software and experimental data.