Critical aspects of using vibrating wire piezometers in geotechnical monitoring of dams: how to meet basic operating principles of the devices and avoid common errors that compromise monitoring


2. Operation of Vibrating Wire Piezometers


2.1. Physical principles, components and operation The operating principle of vibrating wire piezometers can be understood in a manner analogous to the functioning of a tuning fork. According to[11]


, frequency measurement in a vibrating wire transducer involves


two main stages: wire excitation and the measurement of the vibratory response over time, with the aim of determining its vibration frequency. Vibrating wire sensors consist of a steel wire stretched between two anchoring points fixed to the


structure being monitored, as illustrated in Figure 1. A coil positioned near the wire generates an electrical impulse that excites the wire and subsequently captures its vibration frequency. This frequency varies according to the tension applied to the wire, which, in turn, is related to the relative displacements of the anchoring points[12]


.


Figure 1. Simplified model of a vibrating wire sensor (Note: 1 – Wire; 2 – Anchoring points; 3 – Coil; 4 – Selector switch; 5 – Input signal; 6 – Damped sensor response signal) (Source: Adapted from[12]


)


The excitation dynamics of the wire are analogous to the classical experiment involving two tuning forks. When one tuning fork is struck, it emits vibrations at its resonance frequency. If a second tuning fork with the same frequency is placed nearby, it also begins to vibrate, even without direct contact (Figure 2). However, if the tuning forks have different frequencies, resonance does not occur.


Vol XXXIII Issue 3 | Dam Engineering | 107


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