responds to all of the prompts, the output is displayed. The displayed output consists of the
dielectric constants, the temperature, the soil moisture, and the soil electrical conductivity.
2.2.2 Trouble Shooting the Analog Hydra Probe
If the Hydra Probe appears to be malfunctioning, there are three likely causes:
!
communication with the logger
!
soil hydrology
!
a malfunctioning probe.
See the section about soil hydrology.
Programming a data logger is not a trivial task. The data logger needs to extract 4 raw voltages
from four analog ports on the logger with the desired timing interval. If the user is unable to get a
response from the Hydra Probe, it is recommended to first physically check wire connections
from the probe to the logger. The user may also want to cycle the power to the probe by
disconnecting and reconnecting both ground wires. If the connections are sound, the user will
next need to check the logger’s setup.
Are the data ports enabled? Are the data ports scaled
properly in the appropriate units? Are the probes and logger adequately powered? Is the data
properly recorded on the logger?
If the logger has GUI based operation software, there may be
a help function. If the logger only accepts terminal command scripts in a terminal window, refer
to the logger’s manual or manufacturer. Also, make sure the computer is properly connected to
the logger.
Is the computer on the proper COM port? What about the Baud rate? Does the
logger need a NUL modem or optical isolator in order to be connected to a computer?
Most of
the technical support questions Stevens receives are not due to malfunctioning probes but rather
an incorrect data logger setup.
A good way to verify if the probe is working properly is to submerge the probe in distilled
water* in a plastic container and check the real dielectric permittivity. Once the probe is
submerged, connect the black and yellow wires to a ground and connect the red wire to a +12
volt DC power source. Use a voltmeter to measure the raw voltage on the 4 data wires. A
common hand held unit is adequate. Use HYDRA.EXE to process the voltages. The temperature
corrected real dielectric permittivity should be 75 to 85 and the imaginary dielectric permittivity
should be less than 5. The user may use this method to verify if the probe is functioning
properly, and to verify the logger output. If the probe is buried in the soil, the user can obtain the
4 raw voltage outputs with a multimeter and compare them to the logger’s output.
*The user may also use tap water for this procedure, however, it is important to note that tap water contains
dissolved material and trace contaminants that might affect the dielectric constants.
2.3 Other Applications and Alternative Calibrations
It may be possible to use the Hydra Probe for applications in media other than mineral soil. Some
examples include peat, decomposed plant material, grain, compost, ice cream/ food products or
any material that has a small real dielectric permittivity compared to that of water. The
calibration curves used to calculate soil moisture may not be valid for material different from
mineral soil; however, the complex dielectric permittivity is provided allowing the user to
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