Casella CEL Nomad portable weather station - Manual (Page 42)

Additional sensors are available for use with “Special Nomad Weather
Systems. They may include sensors to measure:
Soil temperature
Leaf wetness
Grass temperature.
The additional sensors should be ordered at the same time as the weather
station as a “special” system. However, if they are added at a later date, extra
hardware is required in the environmental case for connection and the new
sensors must be configured via the logger or via Online Pro.
Please consult the Casella CEL Sales Office for information on
additional sensor options.
This chapter is divided into separate sections that each describe one of
the sensors available.
Note that Casella equipment is guaranteed for 12 months from date of
dispatch, with the exception of the actual humidity sensing element. It is
impossible for Casella to control or know the environment in which the sensing
element has been used in relation to its performance constraints.
6.2 Combined Air Temperature and Relative
Humidity Sensor
The combined air temperature and relative
humidity sensor is installed within a single
radiation screen that is mounted on a
bracket below the sensor cross arm. Both
transducers are unaffected by condensation
and are resilient to airborne pollution.
The hygrometer is of the
capacitative type and is largely free from
drift. It offers high repeatability over large
ranges of humidity for long periods.
The temperature sensor is based
upon a platinum resistance element to
BS1904, DIN 43760, and incorporates
linearisation electronics within the sensor.
The output from the temperature sensor is
used to compensate the hygrometer for temperature effects.
Outputs from both of these sensors are led to a terminal box on the
sensor cross arm, from where a single sensor cable is taken to the 7-pin socket
on the bottom panel of the environmental case.
6.2.1 Temperature Sensor Specification
Sensor type: Thin film platinum resistance
Measurement range: -40°C to 60°C
Accuracy: ±0.3°C at 0°C
±0.55°C at 50°C
Operating Temperature -40°C to +60°C
6.2.2 Humidity Sensor Specification
Sensor type: Capacitative
Measuring range: 0 - 100% RH
Calibrated accuracy: ±3% RH
Hysteresis: ±1%
Linearity: ±1.5% RH between 5% - 95% RH
Time constant: <10 s between 10% and 90% RH
Standard Sensors
01056
Figure 11: Combined temperature
and relative humidity sensor
Page 42 of 68
NOMAD Portable Weather Station
Users Handbook