• Appendix A. Glossary of Selected Terms
• Appendix B. Bibliography of Time Domain Reflectometry Applicable to Geotechnical Engineering
• Appendix C. Vendors of Equipment for TDR Measurements
• Appendix D. Wiring Diagrams for Data Acquisition Equipment

Appendix A. Glossary of Selected Terms

cable fault: inefficiency in delivering electrical energy by an electrical conductor (cable). Can be caused by crimps, broken cables, water leaking through insulation, or poor splices and connectors.

capacitance: the ability of conductors, separated by a dielectric, to store energy between them.

characteristic impedance: the designed impedance of a cable.

dielectric: insulation. Does not allow electrical energy to flow away from conductor in a cable and also controls the velocity of propagation.

impedance: the sum of the resistance (opposition to DC) and reactance in an electrical cable. Note that it is expressed in ohms as is simple DC resistance.

incident pulse: the electrical pulse sent out by the cable tester. The pulse and its reflections from the cable make up the waveform shown on the cable tester screen.

inductance: the ability of a conductor to produce an induced voltage when there is a variation in the electrical current passing through it.

millirho: 1/1000 of a rho.

noise: electrical energy that interferes with a measurement, generally random. A noise filter averages out the waveforms to approach the real signal, but takes longer to acquire the waveform.

reactance: opposition to the flow of AC energy through a cable. Composed of capacitance and inductance.

reflectometer: instrument that uses reflections from points along a cable to make measurements.

resistance: opposition to the flow of DC energy through a cable.

rho: the reflection coefficient of a cable, that is, the ratio of the voltage applied to a cable divided by the reflected voltage. Almost all the energy is reflected back from the end of the cable (open circuit) so the coefficient is +1. A short circuit means that all energy is returned through the return conductor and the coefficient is -1. If no energy is reflected, the coefficient is 0. Deformations return a coefficient between -1 and 1.

short circuit: place where conductor contacts a return path or ground. Can occur at the end of coaxial cables if inner and outer conductor are allowed to touch.

time domain reflectometry (TDR): sends out pulses of energy and then times the interval until the reflections are received. If the velocity of propagation is known, the distance to deformations can be determined.

velocity of propagation: the ratio of the speed of electrical energy in a cable to the speed of electrical energy in a vacuum (the speed of light).

Appendix D. Wiring Diagrams for Data Acquisition Equipment

• FIGURE D-1. SDM 1502 and CR10 Wiring Diagram.
• FIGURE D-2. Cable Tester Power from CR10.
• FIGURE D-3. Multiplexer/Datalogger Wiring.
• FIGURE D-4. Datalogger/Relay Wiring.
• FIGURE D-5 . Cellular Phone System Wiring.
• FIGURE D-6. Power Supply Wiring.
• FIGURE D-7. TDR Coaxial Cable Wiring.

Last modified 06-23-97