Siting

The general EPA guidance for standard meteorological stations is to locate the sensor over an open, level area at least 9 m (29.5 ft) in diameter. The surface should be covered by short grass or the natural earth where grass does not grow. Sensors should be located at a distance of at least four times the height of any nearby obstruction and at least 30 m (98.4 ft) (EPA) from large, paved areas. Sensors should be protected from thermal radiation and adequately ventilated. Protect the filter at the top of the sensor from exposure to liquid water.

NOTE:

The connector at the base of the removable sensing element is susceptible to corrosion in locations where salt spray or corrosive gases are present. To protect the connector and avoid corrosion, Campbell Scientific recommends applying a small amount of high-vacuum grease around the pins of the connector. That type of grease is designed to have low levels of volatiles and to not outgas.

The sensor should be installed at a standard measurement height, which varies depending on the guides being used:

  • 1.5 m (4.92 ft) (AASC)
  • 1.25 to 2.0 m (4.1 to 6.5 ft) (WMO)
  • 2.0 m (6.5 ft) (EPA)

See Attributions and references for a list of references that discuss temperature and relative humidity sensors.

When used in the field, the HygroVue 5 must be housed in a radiation shield. Typically, the RAD06 unventilated or the TS100SS fan-aspirated solar radiation shield is used.

The white color of these shields reflects solar radiation, and the louvered construction allows air to pass freely through, thereby keeping the sensor at or near ambient temperature. The RAD06 has a double-louvered design that offers improved sensor protection from insect intrusion and driving rain and snow. In addition, compared to shields of a similar appearance, the RAD shields have lower self-heating in bright sunlight combined with low wind speeds giving a better measurement. The RAD06 attaches to a crossarm, mast, or user-supplied pipe with a 2.5 to 5.3 cm (1.0 to 2.1 inch) outer diameter.

The Apogee Instruments aspirated TS100SS shield can also be used where minimal solar errors and a fast speed of response is desired. A special adapter is available to allow the HygroVue 5 to fit within the shield. Refer for the documentation for the TS100SS shield for further installation instructions.

Tools required for installing a radiation shield to a tripod or tower include:

  • Adjustable wrench (to suit 12 mm (1/2 in) nuts)
  • Small screwdriver provided with data logger
  • Small Phillips screwdriver
  • UV-resistant cable ties
  • Small pair of diagonal-cutting pliers
  • Adjustable wrench with a minimum 50 mm (2 in) jaw size