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Standardizing Characterization of Electromagnetic Water Content Sensors

Part 2. Evaluation of Seven Sensing Systems

Dep. of Plants, Soils and Biometeorology, Utah State University, 4820 Old Main Hill, Logan, UT, USA 84322-4820

View larger version (108K): [in a new window]   Fig. 1. Probes of the sensing systems considered in the study are from left to right: Acclima Digital TDT Sensor, three-rod TDR probe used with Tektronix TDR and TDR100 (0.15-m-long 3.20-mm-diam. rods, 12.0-mm rod spacing), CS616, ECH2O Probe, Hydra Probe, and Theta Probe.

View larger version (17K): [in a new window]   Fig. 2. Deviation of higher frequency broadband sensing system ' predictions from the modeled network analyzer ' measurements (reference) in nonrelaxing and nonconducting (NR-NC) media. The frequencies from which the reference ' measurements were taken are in parentheses and are maximum passable frequencies (fmax).

View larger version (18K): [in a new window]   Fig. 3. Deviation of the lower frequency sensing system (excluding CS616 and ECH2O Probe) ' predictions from the modeled network analyzer ' measurements (reference) in nonrelaxing and nonconducting (NR-NC) media. The frequencies from which the reference ' measurements were taken are in parentheses and are reported sensor frequencies. The x axis ranges from 0 to 80 to indicate the measurement range compared with the higher frequency broadband sensing systems (Fig. 2). Note that the CS616 and ECH2O Probe are excluded because the manufacturers do not provide information for permittivity determination.

View larger version (24K): [in a new window]   Fig. 4. Response models fit to the NR-NC media data for the (a) higher frequency broadband sensing systems (model is Eq. [1] fit to the data using an electrical length, Le, of 0.15 m and where the travel times measured with the Acclima TDT are divided by a factor of four to account for 0.60-m waveguide length), (b) CS616, (c) Hydra Probe (response model was not derived for the Hydra Probe because it uses three output voltage values to derive permittivity and the details concerning how this is accomplished were not available from the manufacturer), (d) Theta Probe and ECH2O Probe. The models for the CS616, Theta Probe, and ECH2O Probe are empirical equations fit to the data with TableCurve (Jandel Scientific, San Rafael, CA).

View larger version (14K): [in a new window]   Fig. 5. Deviation of higher frequency broadband sensing system ' predictions (from response model) from modeled network analyzer ' measurements (reference) in relaxing and nonconducting (R-NC) (Table 2) media as relaxation increases. The frequencies from which the reference network analyzer ' measurements were taken are the individual maximum passable frequencies (fmax) of the sensing systems in the three R-NC media samples (glycerol, Brasso, and 1-propanol). It should be noted that the fmax values in R-NC media are reduced by approximately 1 GHz compared with the nonrelaxing and nonconducting (NR-NC) media.

View larger version (16K): [in a new window]   Fig. 6. Deviation of lower frequency sensing system (excluding the CS616 and ECH2O Probe) ' predictions (from software for Hydra Probe and response model for Theta Probe) from modeled network analyzer ' measurements (reference) in relaxing and nonconducting (R-NC) media (Table 2) as relaxation increases. Note that the CS616 and ECH2O Probe are excluded because their measurement frequencies in R-NC media and cannot be estimated from Eq. [3] or inferred from network analyzer data (manufacturers do not provide information for permittivity determination).

View larger version (13K): [in a new window]   Fig. 7. Deviation of higher frequency broadband sensing system ' predictions from the ' prediction where electrical conductivity (b) = 0.0 dS m–1 (reference) as nonrelaxing and conducting (NR-C) sample b increases from 0.0 to 2.0 dS m–1. The NR-C sample used here has a s = 40.0 (Table 2).

View larger version (13K): [in a new window]   Fig. 8. Deviation of higher frequency broadband sensing system ' predictions from the ' prediction where electrical conductivity (b) = 0.0 dS m–1 (reference) as nonrelaxing and conducting (NR-C) sample b increases from 0.0 to 2.0 dS m–1. The NR-C sample used here has a s = 78.5 (Table 2).

View larger version (14K): [in a new window]   Fig. 9. Deviation of lower frequency sensing system (excluding ECH2O Probe; see Fig. 10) ' predictions from the ' prediction where electrical conductivity (b) = 0.0 dS m–1 (reference) as nonrelaxing and conducting (NR-C) sample b increases from 0.0 to 2.0 dS m–1. The NR-C sample used here has a s = 40.0 (Table 2).

View larger version (11K): [in a new window]   Fig. 10. Deviation of ECH2O Probe ' predictions from the ' prediction where electrical conductivity (b) = 0.0 dS m–1 (reference) as nonrelaxing and conducting (NR-C) sample b increases from 0.0 to 2.0 dS m–1. The NR-C sample used here has a s = 40.0 (Table 2).

View larger version (15K): [in a new window]   Fig. 11. Deviation of higher frequency broadband sensing system ' predictions from modeled network analyzer ' measurements in nonrelaxing and nonconducting (NR-NC) media with a temperature (T) range of 5.38 to 39.5°C (Table 2). The NR-NC sample used here has a s = 38.5 to 41.3 (Table 2).

View larger version (15K): [in a new window]   Fig. 12. Deviation of higher frequency broadband sensing system ' predictions from modeled network analyzer ' measurements in nonrelaxing and nonconducting (NR-NC) media with a temperature range of 5.05 to 40.0°C (Table 2). The NR-NC sample used here has a s = 73.4 to 86.1 (Table 2).

View larger version (18K): [in a new window]   Fig. 13. Deviation of lower frequency sensing system ' predictions from modeled network analyzer ' measurements in nonrelaxing and nonconducting (NR-NC) media with a temperature (T) range of 5.38 to 39.5°C (Table 2). The NR-NC sample used here has a s = 38.5 to 41.3 (Table 2).