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Evaluation of Uncoated and Coated Time Domain Reflectometry Probes for High Electrical Conductivity Systems

Dep. of Earth and Ocean Sciences, Univ. of British Columbia, 6339 Stores Road, Vancouver, BC, Canada V6T 1Z4

View larger version (13K): [in a new window]   Fig. 1. Schematic of TDR probe design: (1) F660 BEF Commscope 75 ohm RG6 coaxial cable; (2) female F-connector; (3) male F-Connector to plug; (4) polyethylene terminal block; (5) 3.2-mm diam. 316 stainless steel rod; (6) 3.2-mm diameter 316 stainless steel rod, optionally coated with 0.4-mm thick polyolefin heat shrink; (7) On Semiconductor MPN3404 PIN diode; and (8) terminal block sealed with a silicon sealant.

View larger version (20K): [in a new window]   Fig. 2. Raw time domain reflectrometry waveforms with manually determined tangent lines to the probe end reflection for a 160-mm length uncoated probe.

View larger version (33K): [in a new window]   Fig. 3. Remote diode shorting method waveforms for diodes located at the probe head (A, B) and at the probe base (C, D) for a 160-mm length uncoated probe in water solutions of varying electrical conductivity.

View larger version (34K): [in a new window]   Fig. 4. Manual probe shorting method waveforms for short circuits created using copper wire located at the probe-head end (A, B) of the exposed conductors and at the probe base end (C, D) of the exposed conductors for a 160 mm length uncoated probe in water solutions of varying electrical conductivity.

View larger version (16K): [in a new window]   Fig. 5. Automated remote diode shorted method measured two-way travel time, travel time measured using manual probe shorting and waveform differencing and travel time calculated from Hasted (1973) data for a 160-mm length uncoated probe in water solutions of varying electrical conductivity.

View larger version (25K): [in a new window]   Fig. 6. Raw time domain reflectrometry waveforms with manually determined tangent lines to the probe end reflection for a 281-mm length coated probe in water solutions of varying electrical conductivity.

View larger version (36K): [in a new window]   Fig. 7. Remote diode shorting method waveforms for diodes located at the probe head (A, B) and at the probe base (C, D) for a 281-mm length coated probe in water solutions of varying electrical conductivity.

View larger version (11K): [in a new window]   Fig. 8. Automated remote diode shorted method measured two-way travel time for a 281-mm length coated probe in water solutions of varying electrical conductivity

View larger version (39K): [in a new window]   Fig. 9. Remote diode shorting method waveforms for diodes located at the probe head (A, B) and at the probe base (C, D) for a 281-mm length coated probe in silica sand saturated with water solutions of varying electrical conductivity

View larger version (16K): [in a new window]   Fig. 10. Measured two-way travel time for 281-mm length coated probe in silica sand saturated with water solutions of varying electrical conductivity (A, B) and water of varying electrical conductivity (C). (A, closed circles) Automated remote diode shorting at both the probe head and end. (B, open circles) Manual dual-tangent fitting to the raw waveforms. (C, closed squares) Measurements in water solutions using automated remote diode shorting at both the probe head and end.

View larger version (31K): [in a new window]   Fig. 11. Relationship of coated probe measured apparent dielectric permittivity to apparent dielectric permittivity: linear correction (A); Eq. [2] using known probe dimensions (B): ro = 12.5 mm, Kc = 2.8 (B); Eq. [2] using ro as fitting parameter (C): ro = 53.5 mm., Kc =2.8.