Delta-T HH2, User Manual

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Technical Reference Moisture Meter User Manual 4.0
Zero mm Deficit
The default root depth in the HH2 is zero. If you do not enter a root depth for your soil
you will get zero for mm deficit.
Do not assume that the default values for Field Capacity pre-set in the HH2 will give
reliable results for your particular soil. It is much better to independently measure it
enter it into the HH2. See Calculating Field Capacity on page 108.
Negative readings
Negative soil moisture readings can be obtained at very low soil moisture values.
This can be frustrating and confusing.
This can be a result of the approximation used when representing a large population
of empirical test data of soil moisture vs. permittivity as a simple equation or table.
The error indicates a limitation of the permittivity based methods of soil moisture
measurement.
Note the impact of the soil moisture coefficient a
0
in the following equation when
water values are low:-
Water content θ = (√ε – a
0
) /a
1
where √ε is the square root of the dielectric permittivity of the soil
and the soil parameters a
0
=1.6 and a
1
=8.4 are used to represent a Mineral soil.
When √ε is less than 1.6 (i.e. in very dry soil) the meter will report a negative reading.
This is a consequence of the fact that no two soils are exactly the same.
The permittivity measurement method is sufficiently good for most purposes, using
generic look-up tables representative of a range of soils. Most users are happy to use
the generic Mineral Soil calibration provided by us.
If necessary you may calibrate your own soil and derive and enter your own soil
parameters a
0
and a
1
.
Dataset Import Wizard reports 'Unexpected error 0x80041004' in a HH2 dataset.
This is what you get when you open a HH2 dataset CSV file in Excel, then save it
using Save As... .CSV file. Although Excel saves the file according to the .CSV rules
with comma separators etc, the data you get in the file is a .CSV version of what you
see on screen and is subtly different from the original file contents in certain points of
detail: especially spacing and number and date/time formatting. Dataset Import
Wizard expects a file format that is exactly as retrieved from the HH2, and is unable
to interpret the Excel version.