B.2.3 deriving calibration function, B.2.3 – Campbell Scientific TDR Probes CS605, CS610, CS630, CS635, CS640, CS645 User Manual
Page 23
Appendix B. Correcting Electrical Conductivity Measurements for System Losses
The temperature effect is described by:
(
)
(
)
25
T
•
02
.
0
1
•
EC
EC
25
T
−
+
=
[B4]
where
is the electrical conductivity at 25
ºC and
is the electrical
conductivity at other temperatures.
25
EC
T
EC
B.2.3 Deriving Calibration Function
Using the K
p
,
ρ
open
and
ρ
shorted
values for each probe, the uncorrected electrical
conductivity as measured by the TDR100 can be corrected to give accurate EC
values that account for system losses. To do this, a range of EC values is
chosen for
σ
uncorrected
in equation [B5] and
σ
corrected
values calculated for the
chosen range of
σ
uncorrected
.
(
)
p
u
d
uncorrecte
p
shorted
u
d
uncorrecte
shorted
u
p
air
u
d
uncorrecte
air
p
u
d
uncorrecte
p
corrected
K
Z
•
K
•
Z
•
•
Z
K
•
Z
•
•
K
Z
•
•
K
−
σ
+
ρ
+
σ
ρ
ρ
+
σ
ρ
+
−
σ
−
=
σ
[B5]
This equation has a quadratic form. The correction is easier to use if a curve is
fit to the
σ
corrected
values for the chosen range of
σ
uncorrected.
This quadratic is
implemented in the datalogger program to given the final result that is
corrected electrical conductivity. This must be done for each probe.
0
0.75
1.5
0
0.75
1.5
uncorrected EC (siemen/meter)
corrected EC (siemen/meter)
FIGURE B-1. Example of corrected and uncorrected electrical
conductivity values.
The fitted equation for this probe is
2
d
uncorrecte
d
uncorrecte
corrected
•
35
.
0
•
95
.
0
01
.
0
σ
+
σ
+
=
σ
B-3