CS616 and CS625 Water Content Reflectometers
θ
g
wet
dry
dry
m
m
m
=
−
For the bulk density
ρ
bulk
dry
cylinder
m
volume
=
the dry weigh of the sample is divided by the sample tube volume.
The volumetric water content is the product of the gravimetric water content
and the bulk density
θ
θ
ρ
v
g
bul
=
*
k
The average water content for the replicates and the recorded CS616/CS625
period are one datum pair to be used for the calibration curve fit.
8.4 Collecting Field Data for Calibration
Required equipment
1. CS616/CS625 connected to datalogger programmed to measure probe
output period
2. Cylindrical sampling devices to determine sample volume for bulk density,
e.g. copper tubing of diameter
≥
1” and length about 2”
3. Containers and scale to measure soil sample weight
4. Oven to dry samples (microwave oven can also be used)
Data needed for CS616/CS625 calibration are the CS616/CS625 output period
(microseconds) and an independently determined volumetric water content.
From this data, the probe response to changing water content can be described
by a quadratic calibration equation of the form
( )
θ τ
τ
τ
v
C
C
C
=
+
+
0
1
2
2
*
*
with
θ
v
being the volumetric water content (m
3
m
-3
);
τ
, the CS616/CS625
period (microseconds); and C
n
, the calibration coefficient (n = 0..2).
The linear form is
( )
θ τ
τ
v
C
C
=
+
0
1
*
38
Summary of Contents for CS616
Page 2: ......
Page 8: ...Table of Contents iv ...
Page 50: ...CS616 and CS625 Water Content Reflectometers 42 ...
Page 52: ...Appendix A Discussion of Soil Water Content A 2 ...
Page 53: ......
