Precise Measurement Module for Laser Two Frequency Gyroscope-Based Seismometer

We present a precise frequency and amplitude measurement module designed for a multidimensional seismometric system based on set of Laser Two Frequency Gyroscopes (L2FG). The novelty of this system is that the monitoring of tracked vibrations is based on the precise measurement of the frequency deviation of two laser beams with different wavelengths, not on the measurement of the Sagnac Effect. The main measurement functions of the module are performed by a dedicated frequency counter implemented in a medium complexity FPGA device, while the control of the measurement process, fast data processing and transmission are provided using of a popular microcontroller. The use of the modified reciprocal frequency measurement method with linear regression (Ω counter) provides high measurement precision well below 1 Hz@600MHz for measurement gate durations longer than 1 ms.