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  28/07/2002
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Velocity Differentiation Domain (VDD)
how they work, some literature on them, where to get them and how much they cost:
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  photographs

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  basic principles

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  advantages

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  disadvantages

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  general

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  manufacturers

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  literature

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  details

From sowacs archives correspondance

               New Company Formed To Market 
            Soil Moisture Measurement Devices

HydroTek Inc. has recently been formed to develop and market soil
moisture measurement and irrigation management
technology. Their first product, called WAVE-1, delivers new,
cost-effective technology for full-range moisture detection. 

The WAVE-1 will directly provide soil-moisture feed-back to a
Programmable Logic Control (PLC) unit operating pivot
irrigation. HydroTek's WAVE-1 sensor operates on 24VDC +/- 15%
input voltage and produces output current from 4 -20
ma which corresponds to volumetric water content. The WAVE -1 has
been calibrated at the factory to provide full scale
output at 30% water by volume.

The WAVE-1 measures about 22" x 2". The epoxy, electronics
package region is about 1" thick. The sensing element
occupies about 16" of the total length and only the thickness of
a circuit board (.125"). These sensors are packaged for
direct burial, but need not be buried to function properly.

For more information, contact Jerry Pagel at HydroTek, Inc.
509-735-9142 or e-mail: jpagel@owt.com or Marty Grogan at
HydroTek@owt.com




             HydroTek Offers VDD Moisture Sensor

HydroTek has introduced it's Velocity Domain Differentiation
(VDD) moisture sensor. The VDD offers all of the
advantages of TDR (Time Domain Reflectrometry) without posing
comparable signal processing challenges.

HydroTek's proprietary methods and processes employ the natural
variation in propagation rates of electromagnetic
waves through different media. For soil moisture measurement, the
media are soil, water and air. Since air and soil
present nearly identical rates of propagation, most of the
variation in velocity results from variation in water content. An
electromagnetic wave-front is propagated through conductors
located in the soil. Increases in transition times between entry
and exit points indicate how much water surrounds the conductors.
Because of the unique sensing ability of VDD, mist, frost or even
a single drop of water can be detected.

For more information contact, Jerry Pagel, HydroTek, Inc. at
509-735-9142, e-mail: jpagel@owt.com or HydroTek@owt.com
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  other

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Relevant Links

Campbell Scientific
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supports Sowacs

MEA logo Data Logging Application and Measurement Systems Engineers

Aquaflex
Soil Moisture Meter

SMEC logo
Delta-T logo
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ism logo ism120x25.gif PRISM - CMP by Irrigation Scheduling Methods, Inc.

Paltin logo
Research, Products, Consultancy on Real-Time Water Dynamics

Eijkelkamp.com