frequency in Hz. Conversion from frequency to engineering units is possible based on a
knowledge of how the sensor operates, and that is provided by the sensor manufacturer.
Figure 4-2. Internal view of a typical vibrating-wire piezometer sensor
The CRVW3 excites vibrating-wire sensors with a swept excitation (frequency-rich) waveform.
The lowest frequency and highest frequency used in that excitation are customizable by the user.
This lowest-to-highest frequency range represents all expected natural frequencies that the
sensor should produce, including during the most extreme conditions in the environment. By
exciting the sensor in only a certain range, interference from unwanted signals on the wire is
reduced. The level of excitation (12, 5, and 2 VDC) can also be controlled by the user.
The main measurement output from a vibrating-wire sensor is a frequency (in Hz or digits) that
corresponds to the natural resonance vibrations of the wire element embedded within the
sensor. This frequency changes as the phenomenon being measured changes. It is important to
consult the manual of your vibrating-wire sensor to document the highest and lowest
frequencies that are expected as output. Consider the most extreme conditions of the
phenomenon you are measuring. Then consider the highest and lowest frequencies that can be
expected under both of those conditions. Using this information, you will formulate both a low
frequency value and high frequency value to be configured into the CRVW3. This frequency
range is used during excitation and during the read-back of the sensor: only energies within the
specified frequency range are used for excitation, and only frequencies within the window are
processed during sensor response read-out. Frequencies outside the specified range are
ignored. This is one of the ways that the VSPECT technology filters unwanted noise out of your
vibrating-wire measurements.
4.2 VSPECT
®
The CRVW3 uses Campbell Scientific VSPECT technology (U.S. Patent No. 7,779,690) to measure
standard, single-coil-circuit vibrating-wire sensors. Learn about the patented Campbell Scientific
VSPECT spectral-analysis technology at:
CRVW3 3-Channel Vibrating-Wire Data Logger
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