How the System Works
The weather system has two parts: an ITU G2 controller housed
in weatherproof enclosure and the Harvest backend servers. The ITU G2
controller interfaces directly to the sensors, assembles the data into a
log file and then transmits the data via the cellular network to the Harvest
servers. Once data has arrived at the servers it is then process for alarm (eg. frost),
data is published on the harvestalarms.com website
and then finally automated data transfers are done (eg. consent data to council/local government).
The system is configured to send data to the Harvest servers every 30 minutes unless it has alarms
configured in which case it will transmit data every minute when in frost conditions or when a new
event is triggered (eg. pump failure).
All data collected remains the property of the customer. As well as being held on the central Harvest
server cluster all data is also backed up to offsite servers. The Harvest server cluster consists of IBM
servers running in a redundant cluster and connected to the internet through a fiber connection with a
dedicated backup fiber connection.
All automated alarms (eg. frost, pump fail etc) are process by their own server cluster with built in
redundancy. SMS messages are processed via a bank of sixteen Motorola/Telit modems and four ISDN lines are
used for the voice messages. Future expansion includes the addition of SIP lines.
Temperature is measured using digital Dallas one-wire sensors
with a range of -55°C to +125° and an accuracy of 0.5%. Sensors
are calibrated at Harvest to 0.1% at 0°C in an environmental chamber with
a calibrated 0.01% platinum temperature sensor.
Rainfall is measured with a tipping-bucket rain gauge. Older systems
were supplied with the Pronamic gauge (1mm per tip) while all current
systems use the higher accuracy Davis 7852 gauge (0.2mm per tip).
Wind is measured using a Davis 7911 or Tru Track anemometers,
usually mounted directly on top of the weather station.
Humidity is measured using a Honeywell HIH-3610 sensor, which
has a range of 0–90% and an accuracy of 5%. After the humidity
data has been temperature-compensated, the dew point and wet bulb
temperatures are calculated from the humidity and the air temperature.
Soil Moisture is measured using either an Acclima TDT or Aquaflex probe.
Both probes use Time Domain Transmission (TDT) technology which allows for
accurate soil moisture readings.
Other sensors are available, such as leaf wetness, soil temperature,
solar radiation, barometric pressure, flow meters, float switches and
pressure sensors. Other sensors can be interfaced to via spare analog,
digital and SDI-12 inputs.
Every system is configured by default with a frost alarm but
can include other alarms too, eg. heat, wind machine on/off,
pump pressure low, etc. If frost alarms are turned on and the
temperature goes below the set frost alarm temperature, a text message,
voice message or email is sent to the specified user(s). The frost alarm
temperature thresholds and alarm roster can be modified online.
Each sensor can have both a frost alarm and a heat alarm,
and each alarm is specified with two alarm levels and a reset
level. For a frost alarm, a paging message is sent when the
temperature crosses below each of the two alarm levels. No more
alarms are sent until the temperature has crossed back above the
reset level, at which time the system goes back into
"wait for alarms" state. Heat alarms work the same way,
but the temperature must cross above the given temperatures for
an alarm, and back below the reset level to reset.