obstruction, and at least 30 m (EPA) from large, paved areas. Sensors should be protected from
thermal radiation, and adequately ventilated.
Standard measurement heights:
1.5 m (AASC)
1.25 to 2.0 m (WMO)
2.0 m (EPA)
See
(p. 16) for a list of references that discuss temperature and
relative humidity sensors.
When used in the field, the EE181 must be housed in a radiation shield such as the RAD10E
naturally aspirated shields.
The white color of these shields reflects solar radiation, and the louvered construction allows air
to pass freely through, thereby keeping the probe at or near ambient temperature. The RAD10E
uses a double-louvered design that offers improved sensor protection from insect intrusion and
driving rain and snow. In addition, the RAD10E shield has lower self-heating in bright sunlight
combined with higher temperatures (> 24 °C (75 °F)) and low wind speeds (< 2 m/s (4.5 mph)),
giving a better measurement.
The RAD10E radiation shield attaches to a crossarm, mast, or user-supplied pipe with a 2.5 to
5.3 cm (1.0 to 2.1 in) outer diameter. See
(p. 12) for an example of shield mounting.
The optimal location for the EE181 sensor tip inside a multi-plate shield is approximately 1/3 to 1/2
of the way down from the top shield plate. With a ten-plate shield, the tip of the EE181 should be
located around three to four plates down from the top of the shield. See
EE181 Temperature and Relative Humidity Probe
9
