Accurate Determination of Oscillating Mass Displacement in Seismometry Using the Moire Technique

摘要

In this paper, a new method based on the moire technique is presented to calculate the displacement of the oscillating mass in seismometry and other oscillating systems in which the position and displacement of the mass are important. The oscillating system consists of a spring-suspended mass whose position is monitored using the moire technique. To form the moire pattern, two similar Ronchi gratings are used so that they are facing each other without physical contact. One of the gratings is fixed to the oscillating mass and the other to the body of the oscillating system. An arrangement consisting of a laser diode, a narrow slit, and a photodiode was also used to detect and record the signal from the displacement of the moire fringes due to the oscillation of the suspended mass. Also, an algorithm for calculations and conversion of electrical signal into displacement signal is presented. To validate the equations and the proposed algorithm, simulated and real data were evaluated and the results were compared. The results show the high capability and accuracy of the moire technique and proposed algorithm in determining the oscillating mass displacement.