10
1 Introduction
Capacitance based soil moisture probes have been used for irrigation scheduling
purposes for the past 15 years around the world.
Global market trends have however necessitated a revised point of departure for
affordable and practical irrigation scheduling technology and instruments.
AquaCheck (Pty) Ltd, has recognized the shift in global trends. The AquaCheck
probe was therefore specifically developed to address these needs. Its design and
construction is not only flexible enough to interface with the most advanced irrigation
system, but also has the ability to function as a very basic tool for entry level
irrigators.
Five versions of the AquaCheck II probe are available:
o
A BASIC II wireless continuous logging version using a wireless hand-held
logger for data transfer to a PC;
o
An ANALOGUE version compatible to third party analogue loggers.
o
A SDI-12 version compatible to third party SDI-12 loggers.
o
A MODBUS version compatible to third party MODBUS loggers.
o
An AquaGREEN probe (SDI-12 or MODBUS) for greenhouse and turf
applications.
Capacitance sensors measure the dielectric constant of the soil by applying a
voltage between two electric plates (sensor rings). The frequency measured by the
rings varies with the dielectric constant, and this is used to calculate the soil
moisture content of the soil. The sensors are typically positioned at various depths
on a column 32mm in diameter. The current AquaCheck probe range offers six
standard length options varying from 200mm to 1200mm. The 400mm typically has
4 sensors and the 1200mm offers 6 sensor depths (
see page 10 – configuration
).
The column with attached sensors is positioned in the probe shaft and is sealed with
a water resistant resin. After assembly, the sensors are individually calibrated or
normalized to set the default air and water counts for each sensor. The probe also
takes a soil temperature reading at each depth. Each sensor has a built-in
temperature variation compensation factor. Readings from each sensor are
therefore corrected for possible inherent electronic temperature variations.
The probe can be set to take readings at variable time intervals but typically a
reading every 30 minutes (on all 6 sensors) would allow for up to 42 days on-board
storage capacity.
This manual covers the BASIC II wireless version.
