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ECH2O-TE/EC-TM Probe Operator’s Manual
4. Probe VWC Calibration
4. Probe VWC Calibration
The ECH2O-TE and EC-TM have been calibrated in media
types including mineral, organic, and potting soil and rock
wool. The goal of these calibrations was to create a generic
calibration equation that will work in all types of each media,
with an accuracy of better than ± 3% volumetric water content (VWC). If you need more accuracy, you can perform a
media-specific calibration to get the accuracy down to ±1-2%.
For more information on how to perform your own soil-specific calibration, or to have Decagon’s calibration service perform one for you, visit http://www.decagon.com/echo/
calibration.html.
Mineral Calibration
The probes were tested in four types of soil (sand, sandy loam,
silt loam, and clay) at solution electrical conductivities of 0.1
to > 5 dS/m and water contents from 0 to 35% volumetric
water content (VWC). The calibration equation generated
from these tests is:
θ = 1.087 * 10-3* Raw - 0.629
where θ is vol. water content and Raw is the output of the
probe sensors (see appendix). It is worth noting here that this
equation is linear. In fact, the linear fit provided as good a fit
in the mineral soil range as did a higher order polynomial, with
the added benefit that it is relatively easy to work with in datalogger programs, etc. However, one drawback with this
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