TDR Sensor

The TDR Sensor is used for soil water content and electrical conductivity measurement.


A TDR Campbell Scientific TDR100 system is available for water content and electrical conductivity measurement of soil samples.

The TDR system consists of an electromagnetic step pulse generator with a fast rise time, a time equivalent sampling oscilloscope, and a trifilar waveguide. The oscilloscope and the step pulse generator are incorporated into the TDR100 and the waveforms are collected via serial port with a home-made software developed using Labview code. An uncoated, 8-cm buriable probe (Model C6630, Campbell Scientific) is used. The probe has three 3 mm stainless steel rods having 8mm spacing.

The TDR technique for water content measurement is based on the measurement of the velocity of propagation of an electromagnetic signal in the soil. This velocity is related to the dielectric apparent permittivity of the soil which is in turn related to the soil volumetric water content.

Reflection associated with stationary standing wave is used to infer electrical conductivity using probe-specific calibration curve derived using salt solutions of known electrical conductivity.

Access arrangements

We can perform tests on samples provided. Alternatively, access can be provided to individual researchers who wish to determine volumetric water content and electrical conductivity of soil sample.