Davis+VantagePro2+Fan+Aspirated+Radiation+Shield

Question
What is the purpose of the Davis VantagePro2 Fan Aspirated Radiation Shield (6153 or 6163)

Answer
The Fan-Aspirated Radiation Shield (FARS) uses active and passive aspiration to minimize the effects of solar radiation and to provide accurate temperature readings. The fan aspirated radiation shield pushes air through the radiation shield. The passive radiation shield (6152 or 6162) is not 100% effective, and does absorb some heat. To improve accuracy, the air is circulated with a fan. There is also a smaller black body effect at night that will result in lower temperature than ambient temperature at night without fan circulation.

Question
How do I know if I need one where I live?

Answer
The radiation shield efficiency is a function of windpseed (passive air flow), temperatue and solar energy. If you live in desert or southern climates where there is little wind on hot summer days, you can get a temperature rise as much as 3 degF. In these environments, it is recommended. If you live in a coastal environment, there should be enough wind.

Question
Can I upgrade to a fan aspirated unit?

Answer
Yes, please visit: http://www.ambientweather.com/77dafarashki.html

Question
What is the difference between the daytime and 24 hour fan?

Answer
The daytime fan runs on solar power. The 24 hour fan runs on a combination of solar and battery power. The 24 hour fan can be configured to run only during the day. Unless you have a problem with radiant heat transfer from an external source at night, the daytime configuration is recommended. The fan will last longer (they typically last 40,000 hours) when it runs only during the daytime.

Testing Results
For Davis Instruments radiation shield testing results, please visit: []

Discussion
//Source, Davis Instruments Newsletter, February, 2009//


 * Q:** Do I need a fan aspirated radiation shield?

During a cloudless, windless night, a passive radiation shield will also report a temperature that is too high. At night, solar radiation is not the issue, but terrestrial radiation is. (These errors are true for any weather station with a passive radiation shield, not just Davis stations.) In many locations, these conditions happen rarely, but every place on earth has these conditions occasionally, particularly at night. But many of our weather station users do have these conditions often and/or want a station with the highest possible accuracy in all conditions. So our design engineers created an elegant and economical solution: the 24-hour fan aspirated radiation shield. The solar powered fan pulls the air through the shield, and has rechargeable batteries that run the fan all night. The temperature and humidity sensors are then measuring closer to ambient conditions. Tom Raymond, one of our amazing tech support team, recommends a fan aspirated radiation shield when you are in an environment that has relatively no wind flow or very little wind flow, or if you want the best possible accuracy in all conditions. The accuracy of the temperature in the passive radiation shield can vary up to 4 degrees F (2.2 degrees C) depending on the wind speed and solar radiation intensity.
 * A:** First, let's think about what a temperature sensor does. It is simple to think that it measures the temperature of the air around it, and our temperature sensors do a very good job of that, with an accuracy of +/- 1 degree F (+/- .6 degree C). Our passive radiation shield keeps direct sunlight off both the temperature and humidity sensors, allowing them to measure the ambient air temperature/humidity, and is very accurate when there is a breeze flowing through it. But when there is no wind, the air inside the shield is still, and if there is also high solar radiation, it tends to warm up. (And what happens to relative humidity when the temperature goes up? Right, it drops.)