VSPECT® Essentials Improving vibrating-wire noise immunity using spectral analysis

Introduction

Structural and geotechnical engineers often use vibrating-wire sensors to measure strain, pressure, tilt, displacement, and load. These sensors have a reputation for being accurate, stable, and durable—making them well suited for long-term static monitoring. Despite their acceptance, vibrating-wire sensors are sometimes plagued by a susceptibility to external electromagnetic noise. This weakness can produce unusable data, requiring data analysts to devote considerable effort to qualifying their data. This susceptibility to external noise is especially difficult in real-time alarm systems where post-collection analysis is not possible.

This web resource discusses a frequency-domain approach that uses spectral analysis to read vibrating-wire sensors, which improves noise immunity when compared to traditional time-domain methods. Fig. 1 shows this improved noise immunity when a drill motor was turned on near a vibrating-wire strain gage.

Noise immunity graph
Fig. 1. Comparison of noise immunity of time-domain analysis with spectral analysis during a noise event

Although the actual strain changed by only a few tenths of a µstrain during the test, the time-domain analysis gave errors of 12,000 µstrain. As shown by Fig. 2, the spectral analysis gave errors of typically less than ±0.5 µstrain during the same noise event.

y-axis data from previous graph
Fig. 2. Improved noise immunity using spectral analysis with zoomed-in y-axis