Measuring and testing – Meteorology – Naturally occurring radiation
Reexamination Certificate
1999-05-27
2001-06-19
Oen, William (Department: 2855)
Measuring and testing
Meteorology
Naturally occurring radiation
Reexamination Certificate
active
06247360
ABSTRACT:
This invention relates to an aspirated radiation shield for weather sensors. More particularly, a solar powered aspirated shield is disclosed for day and night operation where atmosphere to be measured is drawn into and across the measuring sensors along a path shielded from the effects of outside radiation.
As used in this disclosure, the word “sensor” describes that portion of a weather instrument that directly measures the desired weather parameter, usually temperature or humidity. It may or may not include the rest of the weather instrument, for example such as the required processing and conversion of the analog data at the sensor to the digital readout required by the user.
BACKGROUND OF THE INVENTION
Weather stations for home, agricultural, and industrial use have become increasingly numerous. In such stations, two of the most common measurements taken relate to humidity and temperature. Unfortunately, placement of the measuring sensors is critical. Users of such measuring sensors frequently must place the measuring sensors where thermal radiation conditions can and do create measurement error, especially as related to temperature and humidity. In certain shields for weather sensors, low wind speeds (for example fewer than five miles per hour), can cause obvious errors in temperature measurement. These errors can be quite large—in the range of 5° Centigrade.
Because these weather sensors must be placed in locations where incident radiation effects can introduce error into the desired measurement; the prior art has tried to provide the measuring sensor within a protecting shield. These devices are either passive shields, relying on natural ventilation provided by the wind, or active shields having a fan-induced air flow.
Regarding such passive shields, it is known to place weather sensors in cylindrically shaped louvered housings. The louvers are intended to block radiation from affecting the reading of the sensors. At the same time, these louvers allow the naturally occurring wind to ventilate the chamber containing the sensors.
Unfortunately, at very low wind speeds, these passive sensor shields loose their effectiveness. The louvers are heated by solar radiation. When the louvers become hot, their heat is passed on to the contained sensors.
As radiation effects are reversible, both day and night measurements are affected. The night sky is a cold radiation “sink.”
It is known to provide aspirated housings for weather sensors. In such shields, a fan typically draws air through the shield past a measuring sensor. The outer wall of the ventilated chamber is not shielded from solar radiation. High aspiration rates are required for the heat to be drawn off.
Alternately, in forced ventilation sensors, it is known to draw air over radiation deflecting louvers to a centrally contained sensor. Unfortunately, when the radiation deflecting louvers become warm, the air being drawn over the louvers is heated. Sensor error can result.
SUMMARY OF THE INVENTION
A cylindrical housing is provided with a passive shield of outside protecting louvers and central aspirated flow paths for sensor measurement. First, the surrounding louvers are circular and slope downward at their cylindrical edges so as to deflect radiation outwardly of the shield. Second, these surrounding louvers permit natural ventilation by horizontally blowing wind. Along the upper surface the louvers are each provided with apertures which enables natural convection. This natural convection reduces the tendency of relatively warm air to become trapped within the louvers. Third, the housing and the louvers are given a small spatial separation. To the extent that heating of the louvers occurs, such heat is prevented from having a direct conductive flow path to the central cylindrical housing containing the sensor. Thus, the central cylindrical housing shielded by the louvers provides another layer of insulation. Fourth, a motor driven fan is placed at the top of the central cylindrical flow path. Air is drawn from the bottom of the housing at a screen-guarded circular opening. Air then passes around an aerodynamically shaped radiation baffle into the sensor chamber of the shield. Radiation from below the shield is prevented from having a direct path to the sensor. Fifth, air is also drawn into the walls of the protecting housing along two flow paths. These two paths lie in two concentric spaces between three walls of the sensor chamber. Finally, a solar powered fan motor and battery circuit is provided with a resistor in series with the battery. The fan motor powering circuit enables increased aspiration during direct sunlight hours, limits solar cell charging current to the during sunlight hours, and finally reduces discharge current during non sunlight hours to prolong battery driven fan operation. Maximum uniformity of temperature and humidity measurement is provided.
An advantage of this aspirated design is that air is not drawn over heated surfaces to the sensor. For example, unlike those prior art aspirated shields that draw air over radiation deflecting surfaces, heating of the air routed to the sensor cannot occur.
It is an additional advantage to combine both passively-ventilated shielding with the aspirated shield of this invention. This combination allows relatively low air speeds to be used in the aspiration. As a direct consequence of this construction, fan motor power can be drastically reduced over that found in the prior art. By way of example, in the preferred embodiment of this invention, the motor runs at 0.16 watts during insolation under full sunlight and at 0.08 watts at night.
REFERENCES:
patent: 5591907 (1997-01-01), Stein et al.
Davis Instruments
Oen William
Townsend and Townsend / and Crew LLP
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