A.3.2 an example using cs605, A.3.2 – Campbell Scientific TDR Probes CS605, CS610, CS630, CS635, CS640, CS645 User Manual
Page 18
Appendix A. Discussion of TDR Probe Offset and a Simple Laboratory Method for Calculation
4. Enter Terminal Mode using Options/Terminal Emulator.
5. Press Enter until > appears (the line commands are not case sensitive)
6. Type GVAR then Enter.
7. 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:
ngth
WaveformLe
•
1
datapoints
end
:
end
ngth
WaveformLe
•
1
datapoints
start
:
start
distance
distance
−
=
−
=
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
=
m.
• Measure temperature of water in column
C
4
.
24
:
T
°
=
.
• Determine actual dielectric permittivity of water using following equation
or values in TABLE A-1.
( )
(
)
(
)
(
)
⎥⎦
⎤
⎢⎣
⎡
−
−
−
+
−
−
=
ε
−
−
−
3
8
2
5
3
25
T
•
10
•
8
.
2
25
T
•
10
•
19
.
1
25
T
•
10
•
5791
.
4
1
•
54
.
78
:
T
( )
76
.
78
T
=
ε
( )
T
•
L
:
La
ε
=
m
66
.
2
La
=
• Waveform parameters for PC-TDR
0
.
1
:
Vp
251
:
datapoints
m
5
:
th
WindowLeng
=
=
=
m
0
offset
Probe
m
0.3
length
Probe
=
=
• Start and end index values from terminal emulator mode of PC-TDR as
described above
87
.
169
:
end
44
.
32
:
start
index
index
=
=
• converting waveform index to apparent distance
th
WindowLeng
•
1
datapoints
start
:
start
index
distance
−
=
A-4