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

4. Enter Terminal Mode using Options/Terminal Emulator.

Press Enter until > appears (the line commands are not case sensitive)

Type GVAR then Enter.

It is recommended that step 6 be repeated several times and that the

average values of Start and End be 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: 3.0:L

•

Measure temperature of water in column C4.24:T °

•

Determine actual dielectric permittivity of water using following equation

or values in TABLE A-1.

() () () ()

⎥

⎦

⎤

⎢

⎣

⎡

−−−+−−=ε

−−−

25T

•

8.225T

•

19.125T

•

5791.41

•

54.78:T

()

76.78T =ε

(

)

T•L:La ε=

m 66 .2La =

•

Waveform parameters for PC-TDR

0.1:Vp251:datapointsm 5:thWindowLeng

m 0offset Probe m 0.3length Probe

•

Start and end index values from terminal emulator mode of PC-TDR as

described above

87.169:end44.32:start

indexindex

•

converting waveform index to apparent distance

thWindowLeng•

1datapoints

start

:start

index

distance

−

A-4

1 2 ... 13 14 15 16 17 18 19 20 21 22 23 ... 27 28

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Campbell TDR Manuale Pagina 18

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