Campbell Scientific TDR100 Time Domain Reflectometry Systems - Manual (Page 26)

TDR100
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.
6.2 CR10X and CR23X Datalogger Instruction 119
parameter data
type
value description
SDM address 1: 2 (00)
4
to
(33)
4
Address of TDR100
see Table 5-1
Output option 2: 4 0 Returns L
a
/L
1 Returns vector of n + 9 values from TDR100
with n the number of waveform data points
selected. Elements 1-9 contain key Instruction
119 parameter values. Then next n elements are
reflection waveform values.
2 Returns the waveform plus the first derivative of
the waveform
3 Electrical conductivity option. See section on
probe constants for electrical conductivity
measurements.
Multiplexer and probe 3:
selection
4 See Section 5.1.1 for address protocol
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