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TDR versus Capacitance or FDR

When we talk with scientists at conferences they often want to know the difference between TDR versus capacitance or FDR.  We’ve written a paper about this in our app guide that has been pretty popular, but it can be difficult to find on our website. Here is an introduction and a link if you are interested in learning more.

TDR Sensor Installation (Giulio Curioni, School of Civil Engineering, Univ. of Birmingham)

TDR Sensor Installation (Giulio Curioni, School of Civil Engineering, Univ. of Birmingham)

Capacitance and TDR techniques are often grouped together because they both measure the dielectric permittivity of the surrounding medium. In fact, it is not uncommon for individuals to confuse the two, suggesting that a given probe measures water content based on TDR when it actually uses capacitance.

TDR

10HS capacitance sensor

With that in mind, we will try to clarify the difference between the two techniques. The capacitance technique determines the dielectric permittivity of a medium by measuring the charge time of a capacitor, which uses that medium as a dielectric. We first define a relationship between the time, t, it takes to charge a capacitor from a starting voltage, Vi , to a voltage V, with an applied voltage, Vf.  Read more….

Watch the webinar

In this webinar, Dr. Colin Campbell discusses the details regarding different ways to measure soil moisture and the theory behind the measurements.  In addition, he provides examples of field research and what technology might apply in each situation. The measurement methods covered are gravimetric sampling, dielectric methods including TDR and FDR/capacitance, neutron probe, and dual needle heat pulse.

 

Download the “Researcher’s complete guide to soil moisture”—>

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