Casella CEL Nomad portable weather station - Manual (Page 47)

Units are individually calibrated and provided
with offset and multiplier values
Cable: 3 m cable supplied
6.9 Leaf Wetness Sensor
This is an additional sensor available for use
with “Special” Nomad Weather Systems.
The leaf wetness sensor is
connected by cable to an auxilliary junction
box. Clip this box to the lower part of the
tripod, and connect the output cable to the
7-pin socket in the bottom panel of a special
system environmental case.
The leaf wetness sensor is a low power electronic module in a
waterproof probe, where the active part of the probe consists of three carbon
electrodes. In effect, the sensor is a digital device, being either ON or OFF with
virtually no graduation between the two states. Free water on the sensing
element changes the conduction, switching the output from OFF to ON.
The device is not sensitive to changes in atmospheric humidity.
The installed device may be specified as optimised for either rain, frost
or dew. The rain sensing version incorporates a heater to dry the surface once
rain has ceased, and also to eliminate it’s sensitivity to the formation of dew.
The sensor will respond to a single 1 mm diameter droplet of distilled
water.
6.9.1 Leaf Wetness Sensor Specification
Part number: 187081B
Transducer: Three element carbon electrode
Length: 150 mm
Supply voltage: 9 - 18 V DC
Power consumption: 5 mA Max
Output Calibration Wet =1.5 V approximately
Dry = 0 V
Sensing area 15 x 30 mm
Operating temp. -10°C to +55°C
Cable: 3 m cable supplied
6.10 Grass Temperature Sensor
This is an additional sensor available for use
with “Special” Nomad Weather Systems.
The “grass minimum” sensor is
connected by cable to an auxilliary junction
box. Clip this box to the lower part of the
tripod, and connect the output cable to the
7-pin socket in the bottom panel of a special
system environmental case.
Grass minimum temperature
measurement is achieved by locating a
shielded thermometer at a fixed height
above the grass, supported on a small frame.
Optional Sensors
01062
Figure 18: Leaf wetness sensor
02025
Figure 19: Grass temperature sensor
Page 47 of 68
NOMAD Portable Weather Station
Users Handbook