Figure 4-1. Basic CRVW3 parts
4.1 Measurement theory
A vibrating-wire sensor is designed so that its output corresponds to changes of the
phenomenon in the environment that is being measured. This is done by converting
environmental changes into changes of the tension on a suspended metal wire, which is located
inside the sensor. The natural frequency of the wire changes as the tension changes; therefore, a
change in frequency may be detected as changes in the measured phenomenon. A magnetic coil
circuit is placed near the suspended wire and senses the motion of the wire by picking up the
changes in the magnetic field caused by wire vibrations.
To measure a vibrating-wire sensor, three main steps are taken by the measurement system:
1. Electrical energy is inserted into the coil circuit, creating a changing magnetic field that
excites (plucks, or inserts energy into) the wire.
2. The excitation terminates so that the wire is left to vibrate at its characteristic resonant, or
natural, frequency. The coil circuit is used to electrically capture the motion of the wire
vibrations during this stage.
3. The measurement system processes the time-series waveform captured from the coil to
assess the frequency of the wire vibrations. The basic output of a vibrating-wire sensor is
CRVW3 3-Channel Vibrating-Wire Data Logger
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