The Research For Performance And Self-noise Measure Of Force-balanced Seismometers

Force-balanced seismometers are the result of combing modern electronic technology with seismometry. Besides its advantages over conventional ones, force-balanced seismometers have much more complicacy. Therefore, a thoroughly grasp to the principle of force-balanced seismometers is the start point of seismometer design. It just as Melton's viewpoint: "The design of practical seismographs requires good engineering coupled with an appreciation of the basic principles involved, rather than the creation of esoteric suspension systems or unconventional electronics."Based on a new viewpoint (no essential distinction between feedback seismometers and none-feedback ones; feedback ones can be simplified into its none-feedback equivalents).Some fundamental problems in the design of force-balanced seismometers are studied thoroughly, a series of conclusions are drawn and many formulae are presented also in this dissertation. The main contents and results of this paper are as follows:1 For demonstrating and justifying the conclusions presented in this dissertation, a sample accelerator is designed and produced in detail. It performances as same as being wanted.2 The algorithm for instrument noise measuring is analyzed in simulation mode and practiced in the measuring of FBS₃B's self-noise. Some common topics in instrument noise measuring are detailed and conclusions are got. Besides this, the probable noise sources in seismometers are listed and analyzed. The ways to alleviate noise are given also.3 Prove that there is not essential distinction between feedback seismometers and none-feedback ones. Argue that the law for designing seismometers is to approximate a simple system (2-order or 3-order), which can be carried out easily, to the wanted system, which has ideal performance but can not be carried out easily, by adding some correcting units into the simple one. The wanted system can be substituted by the corrected system and the corrected system will appearing as a high-order system of which performance is similar to that of the wanted system(2-order or 3-order). The order of high-order system can be reduced to 2-order or 3-order. The approximating methods are varied but some of them are optional.4 The influence of feedback network on the dynamic range, resolution, signal-noise ratio and stability of seismometers are analyzed thoroughly. The optional and reasonable way to design the amplification of each component of seismometers are presented. The foundational problems about the resolution of seismometers are detailed also. Additionally, some formulae for calculating resolutions of seismometers are presented.5 Instability of a close-loop control system is a common and knotty problem in system design. Because there are a lot of energy-storing components in a close-loop control system, the system will loss its stability and be out of work if the parameters of partial units are unreasonable-designed, hi this dissertation, the contributions of feedbacknetworks to the system stability are analyzed.6 Basing on a 2-order system, demonstrate how to construct the wanted system by add correcting and compensating unit in. Conversely, the way to simplify a high-order system as a low-order one are also given.7 The ratio of mechanical balance force to electrical feedback balance force in a force -balanced accelerator is give; the way to design the mechanical parameters of the accelerator is presented also.The originality in this dissertation:(1)The relationship of a feedback seismometer's performance and its feedback is researchedsystematically and comprehensively. (2)Prove that there is no essential distinction between feedback seismometers and none-feedbackones. (3)Simplify the feedback seismometers into their equivalent open-loop seismometersand then get the analytical-function of the parameters. (4)Some common issues in instrument noise measuring are analyzed by simulating andconclusions are given.