Page 94 - Thomson, William Tyrrell-Theory of Vibration with Applications-Taylor _ Francis (2010)

Sec. 3.13 Vibration-Measuring Instruments 81

Figure 3.11-4. Ranger seismometer. (Courtesy of Kinemetrics, Inc.,
Pasadena, California.)

of this kind can have a natural frequency from 1 to 5 Hz and a useful frequency
range of 10 to 2000 Hz. The sensitivity of such instruments can be in the range of
20 to 350 mV/cm/s, with the maximum displacement limited to about 0.5 cm peak
to peak.
Both the displacement and acceleration are available from the velocity-type
transducer by means of the integrator or the differentiator provided in most signal
conditioner units.
Figure 3.11-4 shows the Ranger seismometer, which because of its high
sensitivity was used in the U.S. lunar space program. The Ranger seismometer
incorporates a velocity-type transducer with the permanent magnet as the seismic

mass. Its natural frequency is nominally 1 Hz with a mass travel of ± I mm. Its size
is 15 cm in diameter and it weighs 11 lb.

Accelerometer: instrument with high natural frequency. When the
natural frequency of the instrument is high compared to that of the vibration to be
measured, the instrument indicates acceleration. Examination of Eq. (3.11-4)