LWS Dielectric Leaf Wetness Sensor
7
7.3.2 Minutes Dry, Minutes Wet or Contaminated, and Minutes Wet
The Voltage measurement can be further categorized into Minutes Dry,
Minutes Wet or Contaminated, and Minutes Wet as follows:
If
mV < 274
Then
Minutes Dry = Scan Interval in seconds / 60
Else
If
mV >= 284
Then
Minutes Wet = Scan Interval in seconds / 60
Else
Minutes Wet or Contaminated = Scan Interval in seconds / 60
End
If
End
If
Given a 2500 mV excitation, the thresholds of less than 274 mV for dry and
greater or equal to 284 mV for wet are recommended by Meter Environment.
However, the thresholds can be adjusted as needed. Minutes dry, minutes wet
or contaminated, and minutes wet can then be totaled and stored for any given
period (table interval). Minutes wet or contaminated can be considered a wet
condition or a contaminated condition depending on the user’s evaluation of
the sensors condition. The user may also choose to store an average of the
voltage measurement for post processing later.
7.3.3 Interpreting Data
Many leaf wetness applications, such as phytopathology, require a Boolean
interpretation of leaf wetness data. A Boolean threshold is determined by
analyzing a few days of time-series data. The time-series data in FIGURE
was obtained using a 5 Vdc excitation. The sensor yields approximately
445 mV when dry, approximately 475 mV when frosted, and greater than
475 mV when wet. Therefore, a Boolean wetness threshold of 500 mV should
serve well for interpreting these data.
FIGURE 7-3. Typical LWS response
