15
TEROS 12
3.3.2 TEMPERATURE
The TEROS 12 uses a thermistor in the center needle to take temperature readings. This is
more important for measurements near the surface where temperature changes are faster.
The TEROS 12 sensor output temperature is in degrees Celsius unless otherwise stated in
the data logger program, such as in preferences in the ZENTRA software.
NOTE: Even though the sensor head is white, in direct sunlight, the temperature measurement may read high. Use
caution when installing the sensor with the sensor head in the sun.
3.3.3 ELECTRICAL CONDUCTIVITY
EC is the ability of a substance to conduct electricity and can be used to infer the amount
of ions that are present in solution. EC is measured by applying an alternating electrical
current to two electrodes and measuring the resistance between them. Bulk EC is
derived by multiplying the inverse of the resistance (conductance) by the cell constant
(the ratio of the distance between the electrodes to their area). TEROS 12 sensor bulk
EC measurements are normalized to EC at 25
°
C. The bulk EC measurement is factory
calibrated to be accurate within ±3% of measurement from 0 to 20 dS/m. This range is
adequate for most soil and growth substrate applications.
EC measurements above 10 dS/m are sensitive to contamination of the electrodes by skin
oils, etc. Be sure to read
Section 4.2
about sensor cleaning if measuring the EC of salty soils.
3.3.4 CONVERTING BULK EC TO PORE EC
For many applications, it is advantageous to know the EC of the solution contained in the
soil pores (
p
), which is a good indicator of the solute concentration in the soil. Traditionally,
p
is obtained by extracting pore water from the soil and measuring
p
directly, a time-
consuming and labor-intensive process. The TEROS 12 sensor measures the EC of the bulk
soil surrounding the sensors (
b
). A considerable amount of research has been conducted to
determine the relationship between
b
and
p
. Hilhorst (2000) took advantage of the linear
relationship between the soil bulk dielectric permittivity (
b
) and
b
to accurately convert
b
to
p
if the
b
is known. The TEROS 12 sensor measures
b
and
b
nearly simultaneously in the
same soil volume. Therefore, the TEROS 12 is well-suited to this method.
The pore water conductivity (
p
) is determined from
(see Hilhorst 2000 for derivation):
Summary of Contents for TEROS 12
Page 1: ...TEROS 12 ...
Page 3: ...ii TEROS 12 4 4 Customer Support 20 4 5 Terms and Conditions 21 References 22 Index 23 ...
Page 4: ...iii ...
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