Strain measurement using oscillator circuit sensor with high sampling frequency

Abstract

A strain measurement system based on astable multivibrator using CMOS inverter has been developed. This system could omit an amplifier, filter and A/D converter unlike conventional Wheatstone bridge type sensor, because strain is measured by counting frequency of circuit voltage output due to resistance changes of a strain gauge. In the previous studies, it was shown that static strain could be measured with the same level of accuracy as Wheatstone bridge circuit. However, it was found that the sampling frequency for counting was not high (around 1 Hz) and it was difficult to measure dynamic strain. A reciprocal counting method has been applied to the system to improve sampling frequency in this study. Fatigue tests of a notched specimen were carried out and strain was measured during the tests to compare performance between the developed sensor and original sensor. As a result, strain could be measured with high frequency by the developed sensor. It is also found that strain measurements with high frequency could detect crack propagation state during the fatigue tests.