Campbell Scientific CR9000X Measurement and Control System - Manual (Page 259)

Section 7. Measurement Instructions
7-35
Parameter
& Data Type Enter TDR100 PARAMETERS
WaveAvg The WaveAvg parameter is used to define the number of waveform
reflections averaged by the TDR100 to give a single result. A waveform
averaging value of 4 provides good signal-to-noise ratio under typical
applications. Under high noise conditions averaging can be increased. The
maximum averaging possible is 128.
Vp The Vp parameter allows you to enter the propagation velocity of a cable
when using the instruction to test for cable lengths or faults. Vp adjustment
is not necessary for soil water content or electrical conductivity
measurement and should be set to 1.0 for output Option 1, 2, or 3.
Points The Points parameter is used to define the number of values in the displayed
or collected waveform (20 to 2048). An entry of 251 is recommended for
soil water measurements. The waveform consists of the number of Points
equally spaced over the WindowLength.
CableLength The CableLength parameter is used to specify the cable length, in meters, of
the TDR probes. If a 0 is entered for the Option parameter, cable length is
used by the analysis algorithm to begin searching for the TDR probe. If a 1
or 2 is entered for the Option parameter, cable length is the distance to the
start of the collected waveform.
The value used for CableLength is best determined using PCTDR100 with
the Vp = 1.0. Adjust the CableLength and WindowLength values in
PCTDR100 until the probe reflection can be viewed. Subtract about 0.5
meters from the distance associated with the beginning of the probe
reflection.
Note that the specified CableLength applies to all probes read by this
instruction; therefore, all probes must have the same cable lengths.
WindowLength The WindowLength parameter specifies the length, in meters, of the
waveform to collect or analyze. The waveform begins at the CableLength
and ends at the CableLength + WindowLength. This is an apparent length
because the value set for Vp may not be the actual propagation velocity. For
water content measurements, the WindowLength must be large enough to
contain the entire probe reflection for probes with 20 to 30 cm rods. A Vp =
1 and Window length = 5 is recommended.
ProbeLength The ProbeLength parameter specifies the length, in meters, of the probe rods
that are exposed to the medium being measured. The value of this
parameter only has an affect when Option 0, La/L, is used for the
measurement.
ProbeOffset The ProbeOffset is an apparent length value used to correct for the portion
of the probe rods that may be encapsulated in epoxy and not surrounded by
soil or other medium being measured. This value is supplied by Campbell
Scientific for the probes we manufacture. The value of this parameter only
has an affect when Option 0, La/L, is used for the measurement.
Mult, Offset The Mult and Offset parameters are each a constant, variable, array, or
expression by which to scale the results of the measurement.