Apogee TS-100 Manual del usuario - Página 4
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INTRODUCTION
Properties of materials and nearly all biological, chemical, and physical processes are temperature
dependent. Temperature is also a fundamental weather variable. As a result, temperature is perhaps the
most widely measured environmental variable.
Aspirated radiation shields are designed to shield temperature and humidity sensors from incident solar
radiation while maintaining equilibrium with ambient air through fan aspiration. Typical applications of
aspirated radiation shields include air temperature and humidity measurements in weather networks,
often for weather forecasting. Air temperature and humidity are critical input variables for calculation of
evapotranspiration and irrigation scheduling. Aspirated shields are also important in the precise
measurement of air temperature and humidity gradients above the land surface.
Apogee Instruments model TS-100 aspirated radiation shields are made from high-quality injection-
molded plastic with low thermal conductivity, maximum weather resistance, and a gloss white finish for
high reflectivity. The small size makes it easy to work with and reduces the surface area exposed to
incoming radiation. The shield is designed as
a lightweight, low power, and low cost alternative to other
aspirated and un-aspirated shields for air temperature and humidity measurement.
The efficient, low-
power fan draws ambient air into the shield using a rocket nozzle contour to maximize airflow around the
internal sensors. The curved inlet helps draw air into the shield during high cross winds. These unique
properties make the TS-100 ideal for use in
remote locations with limited power supply.
All Apogee TS-100 shields come with a precision air temperature sensor (model ST-110, thermistor). ST-
110 air temperature sensors are weatherproof, have excellent long-term stability, and are designed for
continuous air temperature measurement when housed in the TS-100. ST-110 thermistors offer improved
accuracy over thermocouples. The advantages of thermistors over platinum resistance thermometers
(PRTs) are high signal-to-noise ratio, requirement of only a single-ended channel for measurement, and
lower cost. Accelerated aging tests indicate that the epoxy-encased ST-110 thermistor has a long-term
stability equal to more expensive reference PRTs. However, TS-100 shields are designed to optionally
accommodate PRTs with a custom adapter.
Measurement errors due to thermal conduction of heat to the sensor are minimized by reflective white
heat shrink tubing, and shading of lead wire on the north side of the shield (in the northern hemisphere;
south side of shield in southern hemisphere). Thermal conductivity to the precision thermistor is further
minimized by using constantan wire, which has twenty-fold lower thermal conductivity than copper wire.