Campbell Scientific TDR Probes CS605, CS610, CS630, CS635, CS640, CS645 - Manual (Page 22)

Appendix B. Correcting Electrical Conductivity Measurements for System Losses
electrical conductivity. K
p
is calculated as the ratio of electrical conductivity to
electrical conductance and presented in equation [B3].
G
K
p
σ
= [B3]
With K
p
determined, a calibration equation can be derived that corrects EC
measurements for system losses.
B.2 Detailed Method Description
B.2.1 Collecting Reflection Coefficient with Probes Open and
Shorted
The EC measurement is independent of frequency and uses reflection
coefficient values from locations well after probe reflections have stabilized. A
distance of 200 meters is chosen for the measurement.
The ρ
open
value is collected with the probe suspended in air. The ρ
shorted
value
is collected with the end of the probe rods shorted while suspended in air. ρ
open
and ρ
shorted
values are easily determined using PC-TDR. Set waveform
parameters to:
Average = 4 Points = 20 Start = 200 Length = 1.
Click Get Waveform and adjust graph scale using the Adjust Axes Range button
to allow determination of reflection coefficient to nearest 0.005.
ρ
open
and ρ
shorted
values can also be collected using a datalogger. See Section
B.2.4 , CR1000 Program for Collecting ρ
open
and ρ
shorted
Values , for CR1000
datalogger program that can be used to collect ρ
open
and ρ
shorted
values.
B.2.2 Determining K
p
K
p
is the slope of electrical conductivity, σ, as a function of conductance, G.
Completely immerse the probe rods in a solution of known or measured
electrical conductivity. TABLE B-1 provides KCl amounts for a range of
solution electrical conductivities. Since
σ is zero when G is zero, K
p
is simply
the ratio of the known or measured electrical conductivity to the conductance,
G, measured using equations [B3] and [B1].
TABLE B-1. Standard KCl Solutions
Electrical Conductivity @ 25°C
(decisiemens/meter)
Grams of KCl/liter of solution
111.34 74.2460
12.86 7.4365
1.409 0.7440
0.147 0.0744
B-2