Negative feedback can be applied to an electromagnetic
seismometer through the coil terminals using a Maxwell
impedance bridge to bypass the coil impedance. The application of feedback by this method obviates the need for a second transducer, and permits direct calibration of the feedback seismometer.
Feedback of a simulated ground acceleration proportional
to the acceleration of the suspended mass effectively
increases the mass, lengthening the natural period of the seismometer. Displacement feedback effectively stiffens the spring, decreasing the resonant period, while the seismometer damping can be increased with velocity feedback.
Experimentally determined sensitivity curves obtained
with a Willmore Mk.I. seismometer demonstrate the capabilities of negative feedback in altering the response of the seismometer. A resonant period of 17 sec. corresponding
to an equivalent suspended mass of 1230 kg. is readily obtained.
A discussion of instrument noise in the feedback seismometer is included. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/37207 |
| Date | January 1965 |
| Creators | Meldrum, Robert David |
| Publisher | University of British Columbia |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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