EVALUATION TESTS, NATIONAL GEOPHYSICAL COMPANY SEISMOMETER TYPE 21.
Special rept. no. 21.
UNITED ELECTRODYNAMICS INC PASADENA CALIF
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This report describes the results of the evaluation tests. A table summarizing the results obtained from the tests is presented. Measured or computed values of the various parameters are compared with the manufacturers specifications and with equivalent values for the JohnsonMatheson seismometer. The manufacturers specifications on damping and natural frequency were confirmed by the test. Mass, weight and the maximum travel were not measured. In general, the J-M and National-21 systems are similar. However, thunderstorm activity caused much larger signals on the National-21 than on the J-M system. The magnification of the National-21 system is approximately 40 of that of an equivalent J-M system when used as a current sensitive device feeding a low impedance amplifier. If used as a voltage-sensitive device feeding a high impedance amplifier, the magnification of the National-21 is approximately 65 higher than that of the J-M. Author