METER TEROS 12 - 4. Service; 4.1 Calibrations

18
SERVICE
4. SERVICE
This section contains calibration information, calibration frequencies, cleaning guidelines,
troubleshooting guidelines, customer support contact information, and terms and conditions.
4.1 CALIBRATIONS
Following is a list of the mineral soil, soilless media, and dielectric calibrations for TEROS12,
where  is the VWC (in m
3
/m
3
), where  is dielectric, and where RAW is the raw sensor output,
when read with a METER or third-party data logger.
The TEROS 12 is not sensitive to variation in soil texture and EC because it runs at a
high measurement frequency. Therefore, its generic calibration equation should result in
reasonable absolute accuracy; 0.03 m
3
/m
3
for most mineral soils up to 8dS/m saturation
extract. Its calibration equations are shown below for mineral soil, soilless growing
media (i.e., potting soil, perlite, or peat moss), and dielectric permittivity. However,
for added accuracy, customers are encouraged to perform soil-specific calibrations.
For more information on how to calibrate sensors or to learn about METER calibration
service (calibrations performed for a standard fee), see soil sensor calibration or contact
Customer Support.
4.1.1 MINERAL SOILS
According to METER tests, a single calibration equation will generally suffice for most
mineral soil types with ECs from 0 dS/m to 8 dS/m saturation extract. VWC () is given by
Equation 5:
Equation 5
Θ m
3
/ m
3
( )
= 3.879×10
−4
× RAW − 0.6956
A linear equation is used for the mineral soil calibration because it provides the best
predictions of VWC in the range of VWC found in mineral soils, but this equation reaches
a maximum at approximately 0.70 m
3
/m
3
in pure water. To display data on a scale from
0 to 1.0 m
3
/m
3
, VWC should be modeled with a quadratic equation (which would result in
a1.0m
3
/m
3
in water). However, METER does not recommend this for mineral soils because it
often makes the calibration in the range of VWC found in mineral soil less accurate.
4.1.2 SOILLESS MEDIA
TEROS 12 sensors are calibrated in potting soil, perlite, and peat. The goal is to create a
generic calibration equation that will work in many nonsoil substrates with an accuracy
of better than 0.05 m
3
/m
3
. For higher accuracy, performing a media-specific calibration
should improve the accuracy to 0.01 to 0.02 m
3
/m
3
. The differences between mineral soil and
soilless media calibrations are caused by high-air volume in the organic soils that lowers the
starting (dry media) dielectric of the sensor.