MODELING AND PARAMETER IDENTIFICATION OF GEOPHONE

摘要

Accurate absolute velocity sensing is critical for active vibration isolation (AVI) purposes [1]. Geophone is the most commonly used absolute velocity sensor in the field of AVI, where geophone resonance frequency should be as low as possible in order to measure low frequency vibration. Geophones with low resonance frequency always have large dimensions and need external power supply, which are not cost-effective. The resonance frequency of commercially available geophone that suitable for AVI application is typically at 4～12Hz. Therefore extension of geophone linear response range at low frequency is necessary, which is based on accurate model and parameters of geophone [2]. Manufacturers provide geophone parameters with an error interval, which makes parameter identification of geophone necessary. Shake-table method is one of the classic identification techniques, which needs a collocated, previously identified velocity sensor as reference sensor [3]. And it needs mechanical exciting equipment that limits its application in the field. Masahiro [4] and Frank [5] use impedance method to identify the parameters of a geophone. But geophone is a mechatronics system, thus injecting current can't excite its mechanical characteristics completely, which make impedance method less accurate than Shake-table method [3]. The step release method is a simple, fast and very accurate method for calibrating geophones when used with a system identifier [6]. But its precision is low when the geophone has high damping ratio [7].