Campbell Scientific TDR100 TDR100 Time Domain Reflectometry Systems - Page 35
Soil Electrical Conductivity Effect on Water Content, Measurement
View all Campbell Scientific TDR100 manuals
Add to My Manuals
Save this manual to your list of manuals |
Page 35 highlights
TDR100 cable lengths will be maintained as long as soil electrical conductivity does not prevent a reflection from the end of the probe rods. This is discussed later in this section. Minimizing cable lengths should always be considered in the design of a measurement system using TDR. If long cable lengths are necessary, the adverse effects can be minimized by using low attenuation cable such as RG8. Careful probe design ensures correct probe impedance giving robust reflections. All TDR probes offered by Campbell Scientific are designed to optimize accuracy when longer cable lengths are used. 8.2 Soil Electrical Conductivity Effect on Water Content Measurement The signal at the probe will be attenuated when ionic conduction occurs in the soil solution. This inherent attenuation is used in TDR measurements to determine soil electrical conductivity as described by equation [5]. The presence of ions in the soil solution provides a path for electrical conduction between TDR probe rods. The attenuation of the signal can affect the accuracy and resolution of water content measurements. Figure 8-2 presents a series of waveforms when a solution with an electrical conductivity of 1.0 dS m-1 is added to a soil which has essentially no salt present. Figure 8-3 shows data for solution with high electrical conductivity. water content = 9.5% water content = 25% FIGURE 8-2. Waveforms collected in a sandy loam using CS610 probe with RG8 connecting cable. Volumetric water content values are 10, 16, 18, 21 and 25%. Solution electrical conductivity is 1.0 dS m-1. 29