Model HC2S3 Temperature and Relative Humidity Probe
10
7.2.2 VoltDiff() Instruction
When cable lengths are longer than 6.1 meters or when the sensor is constantly
powered, the
VoltDiff()
measurement instruction is used to measure the
HC2S3 sensor. The output scale is 0 to 1000 mV for the temperature range of
–40 to 60 °C and 0 to 1000 mV for the relative humidity range of 0 to 100%.
VoltDiff
(Dest, Reps, Range, DiffChan, RevDiff, SettlingTime,
Integ/FNotch, Mult, Offset)
Variations:
•
Temperature reported as °C
—
set
Mult
to
0.1
and
Offset
to
-40
•
Temperature reported as °F
—
set
Mult
to
.18
and
Offset
to
-40
•
Humidity reported as a percent – set
Mult
to
0.1
and
Offset
to
0
•
Humidity reported as a fraction – set
Mult
to
0.001
and
Offset
to
0
7.3 Installation
Sensors should be located over an open, level area at least 9 m (EPA) in
diameter. The surface should be covered by short grass or the natural earth
surface 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 (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. The hydrophobic nature of the filter repels light rain,
but driving rain can force itself into the pore structure of the filter and take time
to dry out.
Standard measurement heights:
1.5 m (AASC)
1.25 to 2.0 m (WMO)
2.0 m (EPA)
(p. 15)
, for a list of references that
discuss temperature and relative humidity sensors.
When used in the field, the HC2S3 must be housed in a radiation shield such as
the 41003-5 or RAD10 naturally aspirated shields, or the 43502 motor-
aspirated shield (please refer to the 43502 product manual for installation
details).
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 RAD10 uses a double-louvered design that
offers improved sensor protection from insect intrusion and driving rain and
snow. In addition, the RAD10 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 41003-5 and RAD10 Radiation Shields attach 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 FIGURE
and FIGURE