METER TEROS 54 - Service and Support; Calibration Information; Mineral Soil Calibration

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SERVICE
4. SERVICE
This section describes the calibration and maintenance of the TEROS 54. Troubleshooting solutions
and customer service information are also provided.
4.1 CALIBRATION
METER software tools automatically apply factory calibrations to the sensor output data.
Calibration by the customer is not provided. Please contact Customer Support if a TEROS
54 needs to be recalibrated.
This section includes the mineral soil and dielectric calibrations for TEROS54, where Θ is
the VWC (in m
3
/m
3
), ε is dielectric and RAW is the raw sensor output when read with a METER
or third-party data logger.
The TEROS 54 is not sensitive to variation in soil texture and electrical conductivity (EC)
because it runs at a high measurement frequency. Therefore, its generic calibration equation
should result in high accuracy for most instances; 0.05 m
3
/m
3
for most mineral soils up to
8dS/m saturation extract. Its calibration equations are shown below for mineral soil 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), 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 to 8 dS/m saturation extract. VWC Θ is given by
Equation1:
Θ (m
3
/m
3
) = 1.8543E–08 × mV
3
– 4.1231E–05 × mV
2
+ 3.1015E-02 × mV − 7.7224E+00
Equation1
A third order polynomial is used for the mineral soil calibration because it provides the
best VWC predictions in the VWC range 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 0.0 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 VWC range found in mineral soil less accurate.