Campbell Scientific (Canada) - Time Domain Reflectometry System

Time Domain Reflectometry System

Overview
TDR100 Reflectometer
SDMX50-Series Multiplexers
TDR Enclosure
Soil Water Measurement Probes
Other Soil Water Content Products
Rock Mass Deformation Measurements


Overview Time Domain Reflectometry (TDR) is widely used to measure soil water content, bulk electrical conductivity, and rock mass deformation. TDR measurements are nondestructive and offer excellent accuracy and precision. The principal components of a TDR system are the CSI datalogger, TDR100 Reflectometer, SDMX50-series coaxial multiplexers, interconnecting cabling, and TDR probes. The TDR100 is controlled using Windows software PCTDR or using a TDR100 instruction with a CR1000 or CR3000 datalogger. Typically the system is powered with a user-supplied, deep-cycle battery that is recharged by a 20 watt solar panel. Installations that have access to ac power may be able to use the PS100-8.5 sealed rechargeable battery in a CR1000 installation, or the CR3000's rechargeable battery.

TDR100 Time Domain Reflectometer
	Compact, low-cost reflectometer Designed for use in remote applications Determines volumetric water content and electrical conductivity in soil and other porous media Can be used in rock-mass deformation applications Communicates with SDMX50-series coaxial multiplexers using our SDM protocol CR1000 and CR3000 dataloggers use TDR100 to control operation of the TDR100, supported in: LoggerNet v 3.1 or higher
PCTDR Windows Software
	Included with the TDR100 Displays the waveform during system setup and troubleshooting Displays volumetric water content and electrical conductivity Switches SDMX50 channels Collects waveform and derivative data files Determines probe constant values needed for electrical conductivity measurements

SDMX50-Series Multiplexers The SDMX50-series multiplexers are eight-channel coaxial switching devices used in our TDR System. Three levels of switching allows up to 512 soil water content or rock mass deformation cables to be connected to one TDR100. The multiplexers are controlled by a CR1000 or CR3000 datalogger during automated measurements. The multiplexers can be controlled by the TDR100 when using PCTDR or connected to a PC. Three multiplexer models are available: the SDMX50, SDMX50LP, and SDMX50SP. All provide reliable and programmable channel selection, but are packaged differently to allow flexibility for a range of installation methods.
	The SDMX50 includes: 8-Channel multiplexer with mounting backplate 10" x 12" Environmental Enclosure with mounting hardware Backplate is perforated for strain relief of sensor cables Enclosure Supply Kit (includes cable ties, desiccant, humidity indicator, and conduit putty)
	The SDMX50LP includes: 8-Channel coaxial multiplexer attached to a backplate for use with customer-supplied mounting Cable ties for attaching sensor cable to enclosure backplate
	The SDMX50-SP includes: 8-Channel coaxial multiplexer with small base for mounting on 1" spacing Cable relief bracket for use in a standard CSC enclosure or a customer-supplied environmental enclosure Cable ties for attaching sensor cables to strain relief bracket
Note: Strain relief for coaxial cables in SDMX50-series multiplexers is very important. Forces on multiplexer coaxial connectors from cable weight or tension can damage the multiplexer, resulting in intermittent or catastrophic failure.
TDR Enclosure ENCTDR100
	16" x 18" enclosure that can house the datalogger, power supply, TDR100 and one SDMX50-SP multiplexer White, fiberglass-reinforced polyester Designed to protect TDR system components from weather, condensing humidity, and dust Includes interconnecting SDM and coaxial cabling, grounding wires, enclosure kit and hardware for mounting the enclosure on a pole, tripod mast, or tower leg

Soil Water Measurement Probes CS605
	3-rod design 30 cm long, 0.48 cm diameter, and 4.5 cm spacing between outer rods RG58 cable with user-specified length Maximum recommended cable length of 15 m Pointed, large-diameter rods and large epoxy head allow use in rugged environments
CS610
	3-rod design 30 cm long, 0.48 cm diameter, and 4.5 cm spacing between outer rods Low attentuation RG8 cable with user-specified length Maximum recommended cable length of 35 m. Longer cables can provide good results in some applications Pointed, large-diameter rods and large epoxy head allowing use in rugged environments Recommended when cable lengths greater than 15 m are required
CS630-L
	3-rod design 15 cm TDR probe Maximum recommended cable length of 15 m. a mid-range probe that provides a larger sample volume than the CS640 and the CS645
CS635-L
	3-rod design 15 cm TDR probe suitable for longer cable lengths (up to 115 feet) recommended for high conductivity soils
CS640
	3-rod design 7.5 cm TDR probe Maximum recommended cable length of 15 m. Recommended for very high conductivity soils or laboratory column applications and cable lengths less than 15 m
CS645
	3-rod design 7.5 cm TDR probe Low-loss LMR200DB cable suitable for lengths up to 35 meters Recommended for very high conductivity soils or laboratory column applications

Other Soil Water Content Products available from Campbell Scientific CS616 Water Content Reflectometer CS620 Handheld Water Content Sensor CD620 HydroSense Display for use with the CS620

Rock Mass Deformation Measurements Time Domain Reflectometry is used to detect deformation within a rock mass. The system is commonly used to monitor deformation associated with landslide, mining, and construction activities. A length of coaxial cable, grouted into a borehole, serves as the system's sensor. Electronic pulses are sent down the cable; reflected pulses are related to deformation of the cable or to pre-established reference points (crimps). 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. An electronic pulse emitted by a cable tester (or reflectometer) is transmitted through an attached coaxial cable (Moffit, 1964). Discontinuities along the cable result in partial or total reflection of the signal. Elapsed travel time and reflected signal strength are measured; travel time is indicative of distance to the discontinuity (±2%); reflected signal strength is related to the severity of cable deformation (O'Connor and Dowding, 1984). TDR was applied to measurement of rock mass deformation by Panek and Tesch (1981) and O'Connor and Dowding (1984). A coaxial cable is emplaced in a borehole and grouted into place. Crimps, at measured intervals along the cable, partially reflect the transmitted signal and provide a more accurate scale for correlation of deformational zones to depth (Dowding, Su, and O'Connor, 1989). Crimps appear as small negative polarity events along the trace of the waveform. Events that offset the waveform indicate deformational zones; the polarity of the offset indicates whether a zone is experiencing tensile or shear deformation. The Campbell Scientific TDR system is optimized for remote use. A CR1000 or CR3000 datalogger is housed in a weather-resistant enclosure along with a TDR100 Reflectometer. The datalogger, using Instruction TDR100, controls operation of the cable tester; power is supplied only during measurement. 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. It is also possible to reprogram the datalogger through telecommunications allowing zones of interest to be thoroughly examined. Multiplexers controlled by the datalogger allow the system to test as many as 512 cables. Because of the specificity of preferred coaxial cable to a particular installation, as well as the shipping costs and logistical difficulties associated with transporting long lengths of coaxial cable, Campbell Scientific recommends that customers acquire suitable coaxial cable from a local electrical parts supplier. Literature Cited Dowding, C. H., Su, M. B., O'Connor, K. (1989): Measurement of Rock Mass Deformation with Grouted Coaxial Antenna Cables, Rock Mechanics and Rock Engineering, 22, 1-23. Moffitt, L.R. (1964): Time Domain Reflectometry - Theory and Applications. Engineering Design News, November, pp. 38-44. O'Connor, K. M., Dowding, C. H. (1984): Application of Time Domain Reflectometry to Mining. Proceedings of 25th Symposium of Rock Mechanics, Northwestern University, Evanston, Illinois, pp. 737-746. Panek, L. A., Tesch, W. J. (1981): Monitoring Ground Movements Near Caving Slopes - Methods and Measurements, RI 8585, U.S. Bureau of Mines, Denver, Colorado, 108 p.