Model 107 Temperature Probe
6
Details of 107 probe measurement and linearization of the thermistor output
are provided in Section 8.2, Measurement and Output Linearization
(p. 8).
7.2.1 Therm107() Instruction
The Therm107() measurement instruction programs CRBasic dataloggers to
measure the 107 probe. It applies a precise excitation voltage, makes a half-
bridge resistance measurement, and converts the result to temperature using the
Steinhart-Hart equation. See Section 8.2, Measurement and Output
Linearization
(p. 8), for more information. Therm107() instruction and
parameters are as follows:
Therm107(Dest, Reps, SEChan, VxChan, SettlingTime, Integ/Fnotch,
Mult, Offset)
Variations:
• Temperature reported as °C — set Mult to 1 and Offset to 0
• Temperature reported as °F — set Mult to 1.8 and Offset to 32
• AC mains noise filtering — set Integ/Fnotch to the 60 Hz or 50 Hz
option (see Section 8.3, Electrically Noisy Environments
(p. 9))
• Compensate for long cable lengths — Set SettlingTime to 20000 (see
Section 8.4, Long Cable Lengths
(p. 9))
7.3 Air Temperature Installation
For air temperature measurements, locate probes over an open, level area at
least 9 m (EPA; Section 10, Attributions and References
(p. 11)) in diameter. The
surface should be covered by short grass or the natural earth surface where
grass does not grow. Probes 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.
Standard air temperature measurement heights:
• 1.25 to 2.0 m (WMO; Section 10, Attributions and References
(p. 11))
• 2.0 m (EPA; Section 10, Attributions and References
(p. 11))
• 2.0 m and 10.0 m for temperature difference (EPA)
When exposed to sunlight, the 107 should be housed in a six-plate solar
radiation shield. Six-plate shields offered by Campbell Scientific are models
41303-5A, 41303-5B, or RAD06.
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 RAD06 uses a double-louvered design that
offers improved sensor protection from insect intrusion and driving rain and
snow. In addition, the RAD06 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 41303-5A and RAD06 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. The 41303-5B attaches to a
CM500-series pole or a user-supplied pole with a 5.1 cm (2.4 in) outer
diameter.
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