Instruction manual

CS650 and CS655 Water Content Reflectometers
• CS650 connected to datalogger programmed to measure probe
permittivity
• Cylindrical sampling devices to determine sample volume for bulk
density, such as copper tubing with diameter of ≥ 1 inch and length
about 2 inches.
• Containers and scale to measure soil sample mass
• Oven to dry samples (microwave oven can also be used)
Data needed for CS650 calibration are the CS650 permittivity output and an
independently determined volumetric water content. From this data, the probe
response to changing water content can be described by a function as described
in Section 8.4.2, User-Derived Calibration Equation
(p. 23).
The calibration coefficients are derived from a curve fit of known water
content and probe permittivity output. The number of data sets needed to
derive a calibration depends on the form of the calibration equation. At least
three data sets should be generated to determine whether the linear form is
valid. If a polynomial is to be used, four data sets will determine whether the
function is a quadratic or third order polynomial. Accuracy requirements may
require additional data sets. Consider the expected range of soil water content
and include data sets from the highest and lowest expected water contents.
Collecting measurements of CS650 permittivity and core samples from the
location where the probe is to be used will provide the best on-site soil-specific
calibration. However, intentionally changing water content in soil profiles can
be difficult.
A vertical face of soil can be formed with a shovel. If the CS650 is to be used
within about 0.5 meters of the surface, the probe can be inserted into the face
and water added to the surface with percolation. After adding water, monitor
the CS650 permittivity to determine if the soil around the rods is at
equilibrium.
With soil at equilibrium, record the CS650 permittivity.
Soil hydraulic properties are spatially variable. Obtaining measurements that
are representative of the soil on a large scale requires multiple readings and
sampling. The average of several core samples should be used to calculate
volumetric water content. Likewise, the CS650 should be inserted at least 3
times into the soil recording the permittivitys following each insertion and
using the average.
Remove the CS650 and take core samples of the soil where the probe rods
were inserted. This is necessary for measurement of bulk density. Copper
tubing of diameter ≥ 1 inch and length about 2 inch works well. The tubes can
be pressed into the soil surface.
It is good to take replicate samples at locations around the soil surface. Three
carefully handled samples will provide good results.
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