A length of coaxial cable, grouted into a borehole, serves as the system s sensor. Areas of offset in the resulting trace depict zones of extension or shear along the cable. TDR was originally developed as a system to locate breaks in coaxial transmission cables. Discontinuities along the cable result in partial or total reflection of the signal. A coaxial cable is emplaced in a borehole and grouted into place.
Crimps appear as small negative polarity events along the trace of the waveform.
The Campbell Scientific TDR system is optimized for remote use. A CR10X or CR23X datalogger is housed in a weather-resistant enclosure along with a TDR100 Reflectometer. This significantly reduces power demands. The datalogger digitally stores waveform data from a sequence of cable tests, thus allowing the system to operate in an unattended mode. Data are retrieved via telecommunications.