CS645-L 3-Rod 7.5 cm TDR Probe with Low-Loss Cable
For Very High Conductivity Soils
Up to 25 m cable length
weather applications water applications energy applications gas flux and turbulence applications infrastructure applications soil applications


The CS645 is used in TDR100- and TDR200-based systems. This probe consists of a Santoprene head, three pointed rods, and a low-loss LMR200DB cable. The length of each rod is 7.5 centimeters, allowing the probe to be used in very high electrical conductivity soils or in laboratory column applications (maximum soil bulk electrical conductivity of 5 deciSiemens/meter). The low-loss cable is suitable for lengths up to 25 meters as measured from the tips of the probe's rods to the reflectometer. A similar probe, the CS640, is available for applications using shorter cable lengths (up to 15 meters). The CS640 and CS645 differ only in their cables.

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Detailed Description

The CS645 acts as a wave guide. Impedance along the rods varies with the dielectric permittivity of the surrounding soil. Because the dielectric permittivity of soil primarily depends on the amount of water present, soil volumetric water content can be inferred from the reflected measurements. Soil bulk electrical conductivity is determined from the attenuation of the applied pulse.


Maximum Soil Bulk Electrical Conductivity 5 dS/m
Rod Diameter 0.16 cm (0.063 in.)
Rod Length 7.5 cm (2.95 in.)
Santoprene Head Dimensions 4.5 x 2.2 x 1.0 cm (1.8 x 0.9 x 0.4 in.)


Note: The following shows notable compatibility information. It is not a comprehensive list of all compatible or incompatible products.

Measurement and Control

Product Compatible Note
SDMX50 (retired)
SDMX50LP (retired)
SDMX50SP (retired)
TDR100 (retired)

Frequently Asked Questions

Number of FAQs related to CS645-L: 1

  1. In applications where TDR probes are used to measure soil water content, the maximum distance from the TDR probe back to the TDR100/TDR200 (even through one or more multiplexers) cannot exceed 15 m (50 ft) when using RG58 coaxial cable; the CS605-L, CS630-L, and CS640-L TDR probes have an RG58 cable. When using low-loss coaxial cable, the distance cannot exceed ≈25 m (80 ft); the CS610-L, CS635-L, and CS645-L TDR probes have a low-loss coaxial cable.

    In slope stability and rock mass deformation applications, the maximum coaxial cable length should not exceed ≈1 mile (5,280 ft). The maximum combined length of all SDM cables in the system should not exceed ≈76 m (250 ft).

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