Campbell Scientific TDR100 Time Domain Reflectometry Systems - Manual (Page 29)

TDR100
8 8 consecutive probes are read; the probes are connected to
channels 1, 2, 3, 4, 5, 6, 7, and 8 of the level 1 multiplexer.
Example 2
An entry of 3624:
Entry Description
3
channel 3 is specified for the level 1 multiplexer.
6 channel 6 is specified for the level 2 multiplexer.
2 channel 2 is specified for the level 3 multiplexer.
4 4 consecutive probes are read; the probes are connected to
channels 2, 3, 4, and 5 of the level 3 multiplexer.
6.3.4 Parameter 4: Waveform Averaging
Sets the number of measurements averaged at a given distance from the
TDR100. A value of 4 is recommended. Higher values can be used when
noise is present. Averaging is useful when noise from power sources or when
noise of random nature is superimposed on the reflection waveform.
Averaging is accomplished by collecting n values at a given distance before
collecting values at the next distance increment where n is the value entered in
Average.
6.3.5 Parameter 5: Relative Propagation Velocity
Relative propagation velocity is the ratio of actual propagation velocity for a
transmission line to the propagation velocity in air. A TDR system is typically
comprised of components with different signal propagation properties. The V
p
for a particular component depends on transmission line characteristics such as
the dielectric constant of inter-conductor insulating material. Setting V
p
= 1.0
and using apparent distances simplifies system setup. The displayed position
of a waveform is apparent distance. The value chosen for V
p
does not affect
water content or electrical conductivity measurement. The selected V
p
value
does affect waveform display.
6.3.6 Parameter 6: Points
The number of waveform values used to calculate apparent lengths or collected
as a waveform file. A value of 251 is recommended. A higher value can
provide higher resolution but can also be problematic in noisy environments.
The first data point is a relative zero and corresponds with the value of Cable
Length. If 250 spatial increments are desired to span the desired Window
Length, a value of 251 should be chosen.
6.3.7 Parameter 7: Cable Length (meters)
Cable length is used by the waveform analysis algorithm as the start position to
search for the probe beginning and end. It is an apparent length.
The value for cable length is easily found using PCTDR. Select the probe
using the Multiplexer feature in the Settings menu. Then adjust the cable
length and window length to position the waveform so the distance to the
23