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Appendix B. Correcting Electrical Conductivity Measurements for System Losses

electrical conductivity. K

is calculated as the ratio of electrical conductivity to

electrical conductance and presented in equation [B3].

[B3]

With K

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 PCTDR. 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.

open

and ρ

shorted

values can also be collected using a datalogger. See Section

B.2.4 for CR1000 datalogger program that can be used to collect ρ

open

and

shorted

values.

B.2.2 Determining K

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

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 @ 25º 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

1 2 ... 15 16 17 18 19 20 21 22 23 24 25 26

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