Campbell Scientific Sentek TriSCAN® Manual v 1.2a - Manual (Page 14)

TriSCAN Manual Version 1.2a
Copyright © 1991 – 2004 Sentek Pty Ltd All rights reserved Page 7
How does the TriSCAN sensor work?
Sensor output and measurement units
The TriSCAN sensor provides two outputs.
The first output is a signal of dimensionless frequency (raw count), that is converted via a normalization
equation and then a default or user-defined calibration equation into volumetric soil water content. The
measurement unit is thus volumetric water content (Vol %) or millimetres of water per 100 mm of soil depth.
The second output is also a dimensionless frequency (raw count) that, in conjunction with the first output
signal, is proportional to changes in soil water content and salinity. A proprietary data model processes the
changes of both output signals simultaneously to reflect the changes in soil salinity. The output of the data
model is a nominal Volumetric Ion Content (VIC). Measurement units of VIC can be quantitatively related
(benchmarked) to the soil EC through site-specific soil sampling and analysis.
Figure 2. Sensor output
Both outputs can be presented as dynamic trend changes over a chosen time scale.
Measurement Range and Soil Suitability
The effective measurement range of TriSCAN is between 0 and 17 dSm
-1
in sand, loamy sand and sandy
loam textures (Australian Soil and Land Survey Field Handbook). Use of TriSCAN at salinity levels and soil
textures outside this range is currently unsupported by Sentek.
Resolution and Accuracy
The resolution and accuracy of the sensor can be considered in terms of the two different outputs.
Volumetric Water Content:
The sensor has a resolution of 0.1 mm of soil moisture. Consecutive readings in equilibrated soil have a
coefficient of variation of 0.1%.
The accuracy of the system is dependent upon the similarity of the soil site to that of the original default soil
type used by Sentek. Calibration coefficients based on this default soil type are used in normal operation. If
site-specific (quantitative) values are required, then a calibration procedure is required to be performed
(refer to “Calibration of Sentek Probes” Manual). A high level of accuracy can be attained with careful
calibration.
Raw Data
Soil Water Content
Soil Salinity
+
Soil Water Content
Soil Salinity
+
Model