Casella CEL Indoor air quality monitor - Manual (Page 32)

12.4 Natural Wet Bulb Thermometer
Sensor Specifications
This sensor uses a PRTD covered with a wet
cotton wick (white). The sensing element is
located centrally above the water container with
the wick covering the complete length of the
sensor and extending down to the base of the
water container.
Distilled water is used in the instrument. This rises
under capillary action to the top of the
temperature sensor, where it evaporates under
natural ventilation. This results in a different
thermo-dynamic temperature to that determined
by forced ventilation (i.e. the psychrometer).
The top of the water container has a removable
cap for filling. This also restricts surface water
evaporation from affecting the final temperature.
In addition, the water container has a radiation
shield to stop the water temperature changing due
to direct radiation.
Specification
Sensing Element Platinum resistance wire
Overall Construction Stainless steel sheath
4 mm diameter x 30 mm long
Measuring Range 1
o
C to 60
o
C
Type PRTD PT100 grade 1
0.1% to BS1904/DIN 43760
4 Wire
Response Time (T
90
) 5 minutes
Accuracy ± 0.2
o
C
Connector Type 4 pin socket
Calibration Check once per year
Page 32 of 42
MICROTHERM indoor air quality &
WinIaq Application Software - User Manual