Campbell TDR200, Инструкция по эксплуатации

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TDR200-Based Time-Domain Reflectometry System
20
FIGURE 8-3. Waveforms collected in a sandy loam using CS610 probe
with RG8 connecting cable. Volumetric water content values are
0.10, 0.18, 0.26, 0.30, and 0.37. Solution electrical conductivity is
10.2 dS m
–1
.
The combined effect of long cable runs and high soil electrical conductivity
must be considered when TDR measurements are taken.
8.3 Filtering and Averaging
The following parameters for the TDR200 instruction are available for
improving measurements in noisy environments.
Noise from ac power lines can be reduced by using the Noise Rejection
Frequency setting. Option 50 takes two contiguous measurements that are
exactly 10 ms out of phase to cancel 50 Hz noise. If the WaveAvg parameter is
an odd number, the actual number of averages will be the next highest even
integer. Option 60 takes two contiguous measurements that are exactly 8.33 ms
out of phase in order to cancel 60 Hz noise. If the WaveAvg parameter is an odd
number, the actual number of averages will be the next highest even integer.
The TDR Filter Level setting is used to reduce noise from the TDR trace by
applying a weighted moving average (arithmetic convolution) to the data
points. The filter level determines the number of neighboring values to include
in the weighted average. Acceptable values are 0 (no filtering) to 10 (maximum
filtering). As an example, choosing a Filter Level of 2 will use five measured
values in calculating the final output value: two values prior to the point of
interest, the actual measured point of interest, and the two values after that
point. Each of those points is weighted with the closer points having more
weight than those further away.
The WaveAvg setting is used to define the number of waveform reflections
averaged by the TDR200 to give a single result. A waveform averaging value
of 4 provides good signal-to-noise ratio under typical applications. Under high
water content = 18%
water content = 37%