HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text Free Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Lin, C.-P. Articles by Tang, S.-H. Search for Related Content PubMed Articles by Lin, C.-P. Articles by Tang, S.-H. GeoRef GeoRef Citation Agricola Articles by Lin, C.-P. Articles by Tang, S.-H. Related Collections Soil Methods/Instrumentation Soil Salinity

Accurate Time Domain Reflectometry Measurement of Electrical Conductivity Accounting for Cable Resistance and Recording Time

Dep. of Civil Engineering, National Chiao Tung Univ., 1001 Ta-Hsueh Rd., Hsinchu, Taiwan

View larger version (24K): [in this window] [in a new window]   Fig. 1. (a) The multisection transmission line model of the time domain reflectometry (TDR) measurement system, in which each uniform section is characterized by the geometric impedance (Zp), resistance loss factor (R), complex dielectric permittivity (r*), and waveguide length (L). The transmission line is driven by a source voltage (Vs) with a source impedance (Zs) and terminated in a load (ZL). The input impedance (Zin) is defined as the ratio of line voltage (V) to the line current (I). (b) The associated direct current circuit model, in which Rs is the inner resistance (equal to the source impedance Zs), Rcable is the cable resistance, R is sample resistance, vs is the source voltage (in time domain), and v is the TDR steady-state voltage. (c) A typical TDR waveform showing definition of reflection coefficient (), where t0 is the roundtrip travel time in the probe section, and tcable is the roundtrip travel time in the cable section.

View larger version (35K): [in this window] [in a new window]   Fig. 2. Effect of cable resistance on time domain reflectometry (TDR) waveforms for a variety of electrical conductivities (): (a) measured TDR waveforms compared with that predicted by the full waveform model in this study; (b) measured TDR waveforms in Fig. 5b of Castiglione and Shouse (2003).

View larger version (18K): [in this window] [in a new window]   Fig. 3. Illustration of the nonlinear relationship between the steady-state reflection coefficient with 200-m RG-58 cable and that without cable resistance, in which scaled is the scaled reflection coefficient by the Castiglione–Shouse method (Eq. [12]).

View larger version (20K): [in this window] [in a new window]   Fig. 4. The estimated electrical conductivity (est) using the actual probe constant in three different methods compared with the numerically controlled true electrical conductivity (true).

View larger version (20K): [in this window] [in a new window]   Fig. 5. The estimated electrical conductivity (est) using the fitted probe constant (ß) in three different methods compared with the numerically controlled true electrical conductivity (true).

View larger version (30K): [in this window] [in a new window]   Fig. 6. Examples showing how (a) electrical conductivity , (b) geometric impedance Zp and length L, and (c) dielectric permittivity affect the time required to reach the steady state, with time expressed as the time that includes multiples of roundtrip travel time in the probe section (t0).

View larger version (22K): [in this window] [in a new window]   Fig. 7. Recording time required for the voltage (vt) to reach steady state (v) for probes that are (a) short-circuited, (b) in water of two electrical conductivities, and (c) in open air.

View larger version (24K): [in this window] [in a new window]   Fig. 8. The effect of recording time (t), expressed as the time that includes multiples of roundtrip travel time in the probe section (t0), on the estimated electrical conductivity (t) using the series resistors model with (a) cable resistance Rcable measured and probe constant ß fitted, and (b) Rcable and ß fitted, or using the Castiglione–Shouse method with (c) actual ß determined, and (d) ß fitted.

View larger version (26K): [in this window] [in a new window]   Fig. 9. The effect of recording time (t), expressed as multiples of roundtrip travel time in the lead cable (tcable), on the estimated electrical conductivity (t) using the series resistors model with (a) cable resistance Rcable measured and probe constant ß fitted, (b) Rcable and ß fitted, or using the Castiglione–Shouse method with (c) actual ß determined, and (d) ß fitted.

View larger version (19K): [in this window] [in a new window]   Fig. 10. Electrical conductivity measured by time domain reflectometry (TDR) compared with that measured by a YSI conductivity meter (YSI) using three different models with the probe constant ß measured or fitted.