The Design Of Force-balanced Differential Capacitance Seismometer With Even Oblique Axis

Development of seismology is marked first by seismologic observation techniques, the reification of which is the evolution of seismometers. Comparing with traditional moving-coil transducer, differential capacitance transducer can sense seismic signal with much lower frequency. At the same time, the development of MEMS (Micro Electro-Mechanical Systems) accelerometer makes it possible that MEMS seismometers with characteristics of micromation, high reliability, low power consumption come into reality. So this paper aims to design force-balanced seismometer on the basis of differential capacitance accelerometer.In this paper, firstly mathematical model of pendulum accelerometer is constructed, and its transfer function is deduced. Then it is shown that the principle of differential capacitance accelerometers by theoretical analysis.And then focusing on the design of seismometer. Each component of it is restricted to moving at a 54.7 degree angle to the ground. Three components , named U, V, W, respectively, are evenly distributed on the pedestal with 120 degree of separation .The circuit consists of three parts, including accelerometer circuit, integrating circuit and coordinate transformation circuit.The properties of the seismometer are tested by calibration, such as its sensitivity, frequency response, linearity, noise, SNR, transversal effect, dynamic range and so on. Furthermore, analysis on transfer function is done.Experimental result indicates the characteristics of the seismometer are as follows: (1) frequency band : 0.01Hz-25Hz (2)high sensitivity: about 2300V/m/s (3)good linearity:1% or so (4) low transversal effect:<1% (5)low noise (6)large dynamic range:>120dB...