The Data Acquisition System Of Broad Band Seismic Recorder

Broad band seismic recorder is a three-component, large dynamic range andintellectualized seismic recorder with broad band and high degree of accuracy. It isespecially arresting to use broad band seismic recorder to explore natural earthquake andtomographic earthquake. It not only is economical but also can supply the structural mapwith a rather large depth, thereby, can supply the approach to solve the essential problemof geodynamics. With the ceaseless perfection of instrument, its significance is obviousto explore tentonic characteristics reaching a depth of several hundred kilometers underthe station in virtue of portable seismic recorder in the area with underdevelopedtraffic. Now, GSN,PASSCAL and USArray projects carrying into execution inAmerican all used broad band seismic recorder to do the artificial focus refractive andreflected explosions, record natural earthquake, research deep structure and constitutionof lithosphere and monitor geological disaster. In our country, the research ofgeodynamics in Qingzang tableland is the field focused attention upon all over the world.In order to take a share in international compete in the advancing front field ofresearching in geodynamics in Qingzang tableland, Qingzang tableland laboratory in theCAS geology and physical geography graduate school and Jilin university exploittogether a new broad band digital seismic recorder. Based on this instrument, weestablished a reliable digital earthquake flowing network supplying high-classobservation data, so that can supply indispensable deep information observation systemfor study multi-wave, multi-component and multi-parameter earthquake tomographicimaging.As the seismic recorder mixed recording the artificial focus and natural earthquake,as a result of particularity of long-term field operation, we should consider enough theproblems listing hereinafter while designing broad band seismic recorder:1. Low power, the function of power supply managing;2. A reliable, large capacity data storage system;3. Large system dynamic range;4. The ability of self-test and fault tolerant capability;5. Wide operating temperature range: -20℃ ～ 60℃;6. Small capacity, light weight, taking expediently;Combined with the special application environment, referred to the designexperience, and based on the former research, a new design of broad-band seismographis proposed, the prototype has been finished, and the primary test results are given. Thedesign of data acquisition module is mainly discussed in this article. The maintechniques are in the following: seismic data acquisition system with large dynamicrange is realized by the 24bit ?-Σ conversion set (CS5371/CS5372 and CS5376). Thelarge storage problem is solved by CF card. The less volume, higher reliability andconvenient upgrade and maintenance have been realized using FPGA in the A/Dinterface circuit. In addition, the test circuit makes the field self-diagnosis and moreconvenient field application of the instrument possible.The data acquisition system consists of low-pass detector, preamplifier, 24 bit ?-ΣA/D, and logic control circuit, etc. In order to make the weak seismic signal fit the inputrange of 24bit A/D, two stage preamplifiers direct coupled are adopted. PGA204 with 1and 100 gain as the first stage receives the differential input, amplifies and then outputsas single end. And the second stage is a differential linear amplifier which converts thesingle end signal into differential input signal for reducing the interference of commonmode input.It makes collection circuit of broad band seismic recorder having improvement thatapplication of 24-bit Δ-ΣA/ D converter. It leaves out traditional analog circuit such asfloating-point amplifier and anti-mixture filter, which advances instantaneous dynamicrange and collection precision of system, at the same time, advances integration andreduces volume, so whole weight and power consumption of broad band seismicrecorder falls down.Mass data storage uses CF card as memory medium, by properly process, 50 pins ofCF card can be changed to standard IDE interface with 44 pins. If this interface is joinedwith PC's IDE interface and the written data is operates by standard file format FAT32,data file writing in CF card can dump and process in PC machine conveniently.As the seismograph can record the signal both excited by artificial hypocenter andnature hypocenter, the online test function for higher reliability is more important in thelong field record. The system test function in broad-band seismograph concludes: thedetector, impulse, sine wave and short circuit test. The switch of corresponding testfunctions is finished by the main controller and logic control unit.Finally, the main work and results are concluded, and the further improvements andsuggestions are proposed.