On the Extensometer of a Variable Capacitor Type

Abstract

Descriptions of a newly devised extensometer of a variable capacitor type, and some observational results at Kamigamo and Osakayama Observatories of Kyoto University are given. The principle of this instrument is based on a variable capacitor transducer, and the frequency changes of a crystal oscillator due to the ground strain are multiplied by ten, a hundred or a thousand times. After the comparison with a standard frequency, the differences are recorded on a frequency meter. One millimeter of trace displacement corresponds to a plate movement of about 28 Å of the variable capacitor, and a strain of 2.8×10^-10 is detectable when the standard length is 10 meters. This instrument is stable against the humidity, atmospheric pressure and temperature, and good for the observation of earth tides, crustal deformations and seismic strains.