The patented VSPECT process uses frequency-domain analysis (including the use of Fourier
transforms), interpolation, and digital signal processing (DSP) to identify and eliminate unwanted
noise from the measurement. The process produces a very high-resolution frequency output.
Figure 4-3. Time series and frequency response of a vibrating-wire sensor
Since changes in temperature can impact the density of the vibrating-wire element of the sensor,
a slight change in frequency is expected on the sensor as temperature changes occur. To
compensate for this effect, many vibrating-wire sensors contain a built-in thermistor or other
resistive temperature device. The resistance of the device is measured and converted to
temperature. The temperature at the time of measurement is recorded and can then be used
together with the frequency reading to calculate the value of the output phenomenon in
engineering units (for example, measured value given with its dimensions or units of measure).
The following two sets of graphs illustrate the use of VSPECT to identify a sensor signal in a quiet
and noisy environment. Both graphs were created from the same sensor using the Vibrating Wire
Report created using a VWAnalyzer. The graphs on the left were was generated from a sensor
measured in an electrically quiet environment. While the graphs on the right show an electrically
noisy environment (AC power) similar to what can be seen in a field environment (power lines,
motors, radio signals, etc.).
CRVW3 3-Channel Vibrating-Wire Data Logger
8