SOME FACTS ABOUT LONG-TERM RELIABILITY OF VIBRATING WIRE INSTRUMENTS

Abstract

In this review of a manufacturer's experience during the last 50 years, the durability and stability of vibrating wire (acoustic) monitoring instruments are discussed and statistics on survival rates are presented. The causes of instrument failure are analyzed; the factors that affect and the mechanisms of zero drift are discussed. The relationship between instrument failure and cable laying, manufacturing process, and cable connections is discussed. Analysis shows differences in zero drift between plain strain gauges and complex sensors. Mention is made of the influence of wire behavior and sensor structure. There is discussion of factors that affect wire and sensor structure aging. Special tests on aging are described. Various tests on long-term observation of a wire or a sensor are summarized. Examples are given of instruments still faithfully operating several dozen years after installation. Those examples involve dams in operation. Although reliability factors considered are limited to survival and time stability, some consideration is given to quality of sensor response and to other aspects, such as resonance, that affect reliability. On the basis of an analysis of data from two types of sensors, it is concluded that vibrating wire instruments offer an extremely high degree of stability, accuracy, and durability.