CS640

The CS640 is used in TDR100- and TDR200-based systems. This probe consists of a Santoprene head, three pointed rods, and a standard RG58 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 RG58 cable is suitable for lengths up to 15 meters (50 ft) as measured from the tips of the probe's rods to the reflectometer. A similar probe, the CS645, is recommended for applications requiring longer cable lengths. The CS640 and CS645 differ only in their cables.

The CS640 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.