Campbell CR6 Series, Operator'S Manual

Page: 453 / 690

Section 8. Operation
453
FIGURE 103: Wide Sweep, Low Noise
Additional measurements were made on the same sensor with an electric rotary
drill operated 10 mm from the sensor. The measurements graphed in the figures
Narrow Sweep, High Noise
(p. 454)
and Wide Sweep, High noise
(p. 455)
show the
effect of narrowing the beginning and ending frequencies to reject the electric
motor noise. The narrow measurement reduces the noise and yields a
signal-to-noise ratio of four times better than the wide measurement. Notice that
if the beginning frequency in the wide measurement is much less than 450 Hz, the
60 Hz harmonic is dominate. When the sensor is measured with the drill a an
increased distance (several centimeters), 60 Hz harmonics are much less and not
dominate. Sensors with frequency ranges below 450 Hz should work well even
in the presence of 50 or 60 Hz noise; however, they should be characterized.
Note Check the manufacturer specifications for the sensor frequency
and excitation ranges to help determine the swept frequency range.