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Appendix A. Discussion of TDR Probe Offset and a Simple Laboratory Method for Calculation

5. Enter terminal mode using Options/Terminal Emulator.

6. Hit Enter until get > (the line commands are not case sensitive)

7. Type GMO then Enter. This will return La/L.

8. Type GVAR then Enter.

9. It is recommended that steps 7 and 8 be repeated several times and that the

average values of Start and End used for following calculations.

GVAR returns the uncorrected Start and End. These values must be

converted to distance from index values. This is done as follows:

ngthWaveformLe

1datapoints

end

:endngthWaveformLe

1datapoints

start

:start

distancedistance

⋅

−

=⋅

−

Equations [A3] and [A4] are then used to calculate probe offset.

A.3.2 An Example Using CS605

• Measured TDR probe rod length:

• Measure temperature of water in column

24.

°C.

• Determine actual dielectric permittivity of water using following equation

or values in Table 1.

() () () ()

[

]

25T108.225T1019.125T105791.4154.78:T −⋅⋅−−⋅⋅+−⋅⋅−⋅=ε

−−−

()

76.78T =ε

(

)

TL:La ε⋅=

m 66.2La =

• Waveform parameters for PCTDR

0.1:Vp251:datapointsm 5:thWindowLeng =

m 0offset Probe m 0.3length Probe

• Start and end index values from terminal emulator mode of PCTDR as

described above

87.169:end44.32:start

indexindex

A-4

1 2 ... 11 12 13 14 15 16 17 18 19 20 21 ... 25 26

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