6
Maintenance and Trouble Shooting
If a probe appears to be malfunctioning, there are generally three main reasons that may explain
why a probe may appear to be malfunctioning. The three most common reasons why a probe
may seam to be malfunctioning are:
1)
Improper logger setup or improper wiring,
2)
soil hydrology may produce some unexpected results, and
3)
the probe is defective.
6.1 How to tell if the Hydra Probe is Defective
The Hydra Probe goes through several tiers of quality control testing at various stages of
production; therefore, it is extremely uncommon for a user to encounter a bad probe. Also, the
probes are rugged enough to function for many years buried in soil.
The Hydra Probe is a dielectric constant sensor, therefore if the Hydra Probe is placed in material
with a know dielectric constant, the Hydra Probe’s dielectric constant measurements should
match that of the literature values. Distilled water has a dielectric constant of about 80. The
Hydra Probe when placed in distilled water should have a real dielectric permittivity
(temperature corrected) from 75 to 85 and the imaginary permittivity constant should be less than
5. The Hydra Probe temperature measurement can be verified with a thermometer. Use a clean
plastic container and make sure the probe is completely submerged.
All configurations of the Hydra Probe should have a real dielectric permittivity of about 80 in
water. For special instructions for trouble shooting Analog probes see Section 2.2.3.
If the Hydra Probe produces a temperature corrected real dielectric permittivity of 80 +/-5 in
distilled water, the Hydra Probe is NOT malfunctioning.
If distilled water is not available, the user may use tap water for this procedure. It is important to
note, however, that tap water may contain trace levels of material that may affect the dielectric
permittivities.
6.1.1 SDI-12 Hydra Probe Trouble shooting commands
To verify that the Hydra Probe is functioning properly perform the following commands: Place
the Hydra Probe in distilled water in a plastic container. Make sure the entire probe is
submerged. In transparent mode and with the third parameter set (aM3!), type “
1M3!
”
followed
by “
1D0!
”
(with a probe address of 1 for this example). The typical response of a Hydra Probe
that is functioning properly should be
1+77.895+78.826+2.462
.
From this example, the real
dielectric permittivity is 77.895, the temperature corrected dielectric constant is 78.826, and the
imaginary dielectric permittivity is 2.462. According to factory specifications, the temperature
corrected dielectric constant should be from 75 to 85 and the imaginary dielectric permittivity
should be less than 5. After the probe verification, the user may wish to reset the probe back to
the default parameter set or any other parameter set.
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