Campbell Scientific TDR Probes CS605, CS610, CS630, CS635, CS640, CS645 - Manual (Page 9)

TDR Probes CS605, CS610, CS630, CS635, CS640, CS645
5.3 Electromagnetic Compatibility
All TDR probes are compliant with performance criteria available upon
request. RF emissions are below EN55022 limit.
6. Installation
TDR probes can be installed in any orientation: horizontally, vertically, or at an
angle to the surface. The measured water content is the integral or average of
the water content over the length of the probe rods. The probe rods should be
completely surrounded by the soil or other media being measured. If portions
of the probe rods are exposed to air, the algorithm for analyzing the waveform
reflection may not be able to correctly locate the beginning and end of the
probe rods.
Care must be exercised when inserting probe rods into the soil to minimize soil
compaction around the rods. Compaction can leave air voids along the length
of the rods. The region adjacent to the rod is the most sensitive so voids near
the rods can be a significant source of error.
After the soil is disturbed for probe installation, most soils will experience
rejuvenation of the soil structure with wetting/drying cycle and freeze/thaw
cycles.
TDR probes can be buried or inserted into the soil. The CS605G Installation
Guide should be used when inserting the CS605 and CS610 into the material
being measured. A guide is generally not needed for the smaller diameter
probes.
7. Operation
7.1 Probe Offset for Water Content Measurement
A portion of the TDR probe rods is surrounded by the probe head material and
is not exposed to the material being measured. Probe offset is used to correct
for this. TABLE 5-2 lists offset values for probes manufactured by Campbell
Scientific. These values are entered in the datalogger instruction or in the PC-
TDR software.
7.1.1 Calculating Probe Offset
Probe offset can be calculated using information from PC-TDR. The probe
rods are immersed in water of known temperature, algorithm values are
collected in the terminal emulator mode of PC-TDR, and simple calculations
provide custom offset values. See Appendix A, Discussion of TDR Probe
Offset and a Simple Laboratory Method for Calculation, for calculation
method.
The values listed in TABLE 5-2 were determined using TDR probes with short
cables. The shape of the waveform reflection is affected as cable length
increases, and this can introduce error into the water content measurement.
Using probe offsets determined by the method described in Appendix A,
Discussion of TDR Probe Offset and a Simple Laboratory Method for
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