19
TEROS 11/12
4.1.3 APPARENT DIELECTRIC PERMITTIVITY
Apparent dielectric permittivity (
a
) can be used to determine VWC using external published
equations such as the Topp equation (Topp et al. 1980). Dielectric permittivity is also used for
calculating pore water EC. Dielectric permittivity is given by
Equation 7
ε =
(
2
.
887
×
10
−
9
×
RAW
3
−
2
.
080
×
10
−
5
×
RAW
2
+
5
.
276
×
10
−
2
×
RAW
−
43
.
39
)
2
4.2 CLEANING
If the sensor needles become contaminated with oils from contact with skin or another
source, it is necessary to clean the needles to ensure accurate EC readings in salty soils with
bulk EC greater than 10 dS/m.
1. Clean each needle using a mild detergent such as liquid dish soap and a nonabrasive
sponge or cloth.
NOTE: Avoid detergents that contain lotions or moisturizers.
2. Rinse the sensor and needles thoroughly with tap or deionized (DI) water.
NOTE: Do not touch the needles with an ungloved hand or bring them in contact with any source of oil or other
nonconducting residue.
4.3 TROUBLESHOOTING
Table 3 Troubleshooting the TEROS 11/12
Problem
Possible Solution
Sensor not
responding
Check power to the sensor.
Check sensor cable and stereo plug connector integrity.
Check data logger wiring to ensure brown is power supply, orange is digital
out, and bare is ground.
Sensor reading
too low (or slightly
negative)
Check for air gaps around sensor needles. These could be produced below
the surface of the substrate when the needle contacts a large piece of
material and pushes it out of the way, or if the sensor is not inserted
perfectly linearly.
Ensure the calibration equation being used is appropriate for the media type.
There are significant differences between substrate calibrations, so be sure
to use the one specific to the substrate.
