How The Profile Probe Works - Delta-T Devices PR2 User Manual

How the Profile Probe works

Before you rush out and hammer your access tubes into the soil,
it will help to understand a little about how the Profile Probe
works:
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Soil Moisture
22 %
Profile Probe User Manual 3.0a
When power is applied to the Profile Probe...
...it creates a 100MHz signal (similar to FM
radio).
The signal is applied to pairs of stainless steel
rings....
... which transmit an electromagnetic field
extending about 100mm into the soil.
The field passes easily through the access tube
walls, but less easily through any air gaps.
The water content of the soil surrounding the
rings...
...dominates its permittivity.
(A measure of a material's response to
polarisation in an electromagnetic field. Water
has a permittivity ≈ 81, compared to soil ≈ 4 and
air ≈ 1)
The permittivity of the soil has a strong
influence on the applied field...
...resulting in a stable voltage output that...
...acts as a simple, sensitive measure of
moisture content.
soil
Introduction 9