Re: choose a sensor

[Dave Barnett]

I'm not clear on this explanation for the "Gro·Point" system:

"Gro·Point utilises a single-point, instrument designed for soil moisture
monitoring and irrigation control. The Gro·Point sensor is designed to be
buried in soil and the system uses Time Domain Transmissometry (TDT) to
measure the volumetric moisture content in soils, peat and other porous
materials."

Is this, or is it not Time Domain Reflectometry (TDR)? As far as I
understand the various electronic technologies, there are only resistivity,
capacitive ("Frequency" domain) and TDR (effective dielectric constant of
soils of various moisture content predictably affects velocity of
propagation of an RF signal along a balanced transmission line).
Theoretically, there could be an inductive sensor on the other side of the
Smith Chart to correspond to the capacitive scheme; it doesn't seem likely
to be worth the trouble--but it would probably be patentable, saving the
mumbo-jumbo surrounding the proprietary devices!

I'd like to hear from users (satisfied AND unsatisfied) and the manufacturer
on this.

Dave B.

Dave Barnett

KB1CWT

Technical Specialist I
UMass CEE Dept
Marston Hall 139
Amherst MA 01003
Fax: 413 545-2840