Campbell CS615, Instruction Manual

Page: 9 / 14

CS615 WATER CONTENT REFLECTOMETER
6
0
0.1
0.2
0.3
0.4
0.5
volumetric water content
0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6
CS615 output period (msec)
ec = 0.8 dS/m ec = 1.8 dS/m ec = 3.0 dS/m
CS615 calibration for version 8221-07
FIGURE 2. CS615 Calibration Curves
Figure 2 demonstrates the effect of electrical
conductivity on the calibration. At electrical
conductivity values of 1 dS m
-1
and below, the
calibration shown for 0.8 dS m
-1
works well for a
wide range of soil textures. The calibration
curves for the higher electrical conductivities
show that the slope decreases with increasing
conductivity. The response of the CS615 to
changes in water content at higher electrical
conductivity values is well-behaved up to
approximately 5 dS m
-1
. The calibration can be
approximated from figure 2 if the soil solution
electrical conductivity is known or if soil
measurements are made with the CS615 and
the actual water content is independently
determined. High clay content has a similar
affect on the calibration but the magnitude is
dependent on the clay type.
electrical
conductivity
(dS m
-1
)
calibration
≤
1.0
θ τ τ τ
v
( ) . . * . *
= − + +
0 187 0 037 0 335
2
1.8
θ τ τ τ
v
( ) . . * . *
= − + +
0 207 0 097 0 288
2
3.0
θ τ τ τ
v
( ) . . * . *
= − + +
0 298 0 361 0 096
2
θ
v
is the volumetric water content on a fraction
basis i.e. 0.20 is 20% volumetric water content.
τ
is the CS615 output period in milliseconds.
9.2 CALIBRATION FOR A SPECIFIC SOIL
The calibration relationship between volumetric
water content and CS615 output period for a
specific soil may need to be established if
increased accuracy is needed or if the
composition of the soil deviates from what might
be considered typical. High electrical
conductivity, high clay content, high quartz
content and high organic matter content are
conditions which will affect probe response.
10. SAMPLE PROGRAMS
Sample Program
number
Description
1 Monitor 1 CS615 with CR10
datalogger using Period
Averaging Instruction (P27)
2 Monitor 1 CS615 with 21X
datalogger using Pulse
Count Instruction (P3)
3 Monitor 48 CS615s with 21X
datalogger and AM416
multiplexer using Pulse
Count Instruction (P3)
4 Monitor 48 CS615s with
CR10 datalogger and
AM416 multiplexer using
Period Averaging Instruction
(P27)