4
Measurements, Parameters, and Data Interpretation
4.1 Analog Hydra Probe Output
Parameters V1, V2, V3 and V4 returned by the digital probes correspond to the voltages read
from the analog probe. In almost all applications, V1, V2, V3, V4 and V5 by themselves are of
no interest to most users of the digital Hydra Probe. See section 2.2.3 for analog processing
information.
4.1.1 Raw Voltages V1, V2, and V3.
The first three voltages are the raw signal responses. The Hydra Probe is an impedance based
dielectric spectrometer in that it is determining the complex dielectric permittivity by measuring
the reflected voltages produced by the characteristic impedance of a coaxial wave guide. A
standing wave generated from the reflection of an electromagnetic wave at a radio frequency of
50 MHz. The 50 MHz electromagnetic wave propagates within the wave guide. The soil absorbs
most of the wave. The portion of the wave that reflects back down the wave guide encounters the
emission propagation creating a standing wave. The first three voltages represent the behavior of
the standing wave and thus the complex dielectric permittivity. The direct measurement of the
complex dielectric permittivity from the raw signal responses is the basis behind the other
parameters and makes the Hydra Probe unique among other electromagnetic based sensors.
(Campbell, 1990, Seyfried and Murdock, 2004).
4.1.2 V4
V4 is the raw signal response of the diode thermistor. The diode thermistor is located within the
probe housing. V4 is used to make temperature corrections to the electronics. See Diode
temperature below for more information.
4.1.3 V5
V5 is the raw signal response of the soil thermistor. The soil thermistor is located in the stainless
steel base plate between the tines. It is in close proximity to the soil providing accurate soil
temperature readings from -30 to 40 degrees Celsius. Complex dielectric permittivity is
influenced by temperature. Not only can the Hydra Probe measure soil temperature, it can make
temperature corrections to the calibration curves based on the temperature corrections of the
complex dielectric permittivity. See temperature corrected real and imaginary dielectric
permittivity for more information. See section 2.2.3 for analog processing information.
4.1.4 ADC Reading 1 through 5
The ADC Reading 1 through 5 are the analog to digital values at 10 bits. They are the binary
numbers that correspond to V1 through V5. They are used by Stevens for development or trouble
shooting purposes.
4.1.5 Diode Temperature
The Diode Temperature is the temperature of the electronics within the Hydra Probe housing. It
corresponds to V4. Because the electronics produces a negligible amount of heat while taking a
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