1
CS615 WATER CONTENT REFLECTOMETER
1. INTRODUCTION
NOTE: There is more than one version of
the CS615. This manual is written for
version 8221-07. The version number is
listed on a cable label near the end of the
probe cable. All CS615s are similar in
measurement method but the calibration
varies with version.
The CS615 Water Content Reflectometer
provides a measure of the volumetric water
content of porous media. The water content
information is derived from the effect of
changing dielectric constant on electromagnetic
waves propagating along a wave guide.
The reflectometer output is a square wave and
can be connected to Campbell Scientific
dataloggers CR10X, CR10, CR500, 21X, or
CR7. The measured period can be converted
to volumetric water content using calibration
values.
2. DESCRIPTION
The Water Content Reflectometer consists of
two stainless steel rods connected to a printed
circuit board. A shielded four-conductor cable is
connected to the circuit board to supply power,
enable the probe, and monitor the pulse output.
The circuit board is encapsulated in epoxy.
High speed electronic components on the circuit
board are configured as a bistable multivibrator.
The output of the multivibrator is connected to
the probe rods which act as a wave guide. The
oscillation frequency of the multivibrator is
dependent on the dielectric constant of the
media being measured. The dielectric constant
is predominantly dependent on the water
content. Digital circuitry scales the multivibrator
output to an appropriate frequency for
measurement with a datalogger. The CS615
output is essentially a square wave with an
amplitude swing of
±
2.5VDC. The period of the
square wave output ranges from 0.7 to 1.6
milliseconds and is used for the calibration to
water content.
FIGURE 1. CS615 Water Content Reflectometer
+12 V
Red
ground
Black
output
Green
enable
Orange
shield
Clear
