Development of vibration environment for calibration ultra-low-frequency seismometers

Waveform distortion is a key factor that influences the calibration precision in the standard sine vibration metrology. A new method is proposed to realize the ultra-low-frequency and low-distortion vibration environment in the vibrator. The causes for waveform distortion, including nonlinear effect of supporting spring, nonuniformity of magnetic flux distribution in air gap, harmonic distortion of driving current, moving damping, are analyzed and then by the technology of feedback, a new kind of device is proposed as a solution to the above problems. The simulation results show that this device could be used to realize more perfect vibration environment, and the displacement distortion can be reduced to less than 0.2% when the vibration frequency is lowed to 0.01Hz. The device has been used for calibration of ultra-low-frequency seismometers.