ZigBee Wireless Soil Moisture Sensor Design for Vineyard ...

3.2.1 Predicting Dew Point and Managing Frost
The dew point temperature is the temperature at which water vapour in the air
will condense into dew, frost, or water droplets given a constant air pressure. It
can be defined as the temperature at which the saturation vapour pressure and
actual vapour pressure are equal. At this temperature the humidity is 100%.
The dew point temperature together with relative humidity can be used to
determine the moisture content in the air. A dew point temperature below 0 °C
is referred to as the frost point because frost is produced when the air cools to
that temperature [19]. When the frost point is about to occur it is important to
take action beforehand otherwise severe damage may occur (refer to Figure
17).
Figure 17: Frost Damage [20]
The dew point temperature can be calculated at a particular temperature and
pressure. By using Magnus formula [21] the saturation vapour pressure and
dew point can be calculated, at a temperature T (in °C ). The saturation
vapour pressure EW (in hPa) over liquid water can be expressed as equation 1
[22].
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