User's Guide

CHAPTER 1. OVERVIEW 3
1.2.1 Vibrating Wire Sensors
Vibrating wire sensors are class of sensor that are often used in
geotechnical or structural monitoring applications.
The sensor contains a steel wire that is attached to a mechanical
system which converts the property being measured to an increase
or decrease in the length of the steel wire. This change in the length
of the wire corresponds to a change in the resonant frequency of
the wire.
An electromagnetic coil is located close to the steel wire. To
read the resonant frequency of the wire it is electronically ‘plucked’
by sending a swept sine signal to the coil. This causes the wire
to vibrate and the resonant frequency is sensed by measuring the
frequency of the voltage induced in the coil.
The ability to read the property from the sensor using frequency
means that the signal is resilient to electrical noise, changes in the
cable resistance and a number of other problems that affect other
types of sensors. The only downside to reading the sensor using
frequency is that the mechanical components and the wire itself
are typically very sensitive to temperature. To overcome this prob-
lem, vibrating wire devices are fitted with integrated temperature
sensors to enable accurate temperature compensation.
Vibrating wire sensors support reading many types of environ-
mental and structural values, including:
• Strain Gages
• Crack sensors (linear displacement)
• Strandmeters
• Extensometers
• Settlement Sensors
• Pressure Cells
• Load Cells
• In-Place Inclinometers
• Stress Meters
1.2.2 Compatibility
The FlatMesh Vibrating Wire Nodes have been designed to be sen-
sor agnostic. The system is designed to work with devices that have