Master of Science (MS)
Physics and Astronomy
The measurement of ground motion is important for a wide range of fields. In physics, advanced experiments can involve precise positioning of components. In civil engineering, engineers need to know the characteristics of ground motion to better design large scale structures, and the study of ground motion form distant earth quakes help geologists understand the structure and dynamics of the earth. Each application requires instruments of different specifications. In this thesis I describe the design, fabrication, assembly, and operation of two broad band force balance seismometers and the associated control software. The design, control elements, and methods used in this project can be extended to other applications were specific criteria are needed in the development of custom seismic sensors. A proportional, integral, and derivative (PID) control scheme was written for the negative feedback loop. Along with the control software, I include a user interface to control the feedback and assist in loop tuning. Closed loop operation of each seismometer was successfully accomplished and the step responses were compared to the step response of an ideal model of the seismometers developed in software. Three parameters are useful in the description of a step response: the settling time, overshoot, and deadtime. The ideal model step response has a settling time of 0.09 seconds and an overshoot of less than 30%. The seismometers exhibit settling times of 1 second and 0.5 seconds and overshoots of 20% and 10%. The ideal model does not exhibit a deadtime but the actual seismometer deadtime was just 30 ms.
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Weber, Andrew, "Design, fabrication, and operation of two broadband force balance seismometers" (2009). LSU Master's Theses. 164.
Johnson, Warren W.