Capacitive frost depth indicator
Laen...
Kuupäev
2018
Kättesaadavus
Autorid
Ajakirja pealkiri
Ajakirja ISSN
Köite pealkiri
Kirjastaja
Abstrakt
The depth of soil freezing
, i.e., the depth at which water is frozen, is a significant
factor
in meteorology, as it affects many processes in agriculture, building, etc. Soil frost penetration is
an important factor for overwintering organisms, but also for physical and chemical processes in
soil, particularly for its mechanical properties. The de
pth of freezing is normally determined
directly, i.e. mechanically, using a special soil
freezing meter, i.e., frost
-
depth
indicator,
according to the process of water freezing in the probe. Another method lies in determining the
soil temperature by the in
terpolation of the curves from the graph, as measured by soil
thermometers according to the change in the resistivity of soil or water, when frozen. The
principle of the
frost
-
depth
indicator
function is to evaluate the
temperature dependence of
water
perm
ittivity, which decreases, when water is frozen, from
ε
r
~ 87 at 1
°C
to ε
r
~ 3.2 at
-
1
°C
,
typical for ice.
The water permittivity is evaluated by a measuring capacitor, which is adapted
into the shape of the frost depth indicator probe,
whose dielectric
is deionized water. During
freezing, the capacity is reduced in this area. The capacity of the partially frozen probe is directly
proportional to the length of its non
-
frozen section. The measuring capacitor is a part of the
resonant circuit of the oscilla
tor. The frequency of the oscillator varies with the capacity of the
probe and is further evaluated. The achievable measurement accuracy is approximately 2% for
the probe of a 1m length and in direct evaluation by an autonomous counter. For the computer
ev
aluation, with the possibility to compensate the probe non
-
linearity, the measurement accuracy
is approximately 0.5%.
Kirjeldus
Article
Märksõnad
depth of soil freezing, capacity measurement, water permittivity, articles