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| Weather Instruments |
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| Figure 1. -- 1-Wire Instrument, Rain Gauge, Radiation Shield (with Humidty and Temperature Sensor) |
Weather Software
The software that runs this weather station consists of a number of tasks, which run at specified intervals. Some tasks are responsible for reading the weather instruments;
other tasks are responsible for formatting the data and posting it to logs and weather web sites.
Wind Speed
The wind speed task samples wind speed every three seconds and places each sample into a buffer, averaging over
a two-minute sliding window. It calculates the minimum and maximum wind speed every sample period.
Wind Direction
The wind direction task samples the wind direction every five seconds and places each sample into a buffer, averaging
over a two-minute sliding window. The averaging algorithm uses consensus averaging.
Temperature
The temperature task samples the temperature sensor once a minute and places the data in a buffer, averaging over a ten-minute
sliding window, and calculating the minimum and maximum temperature every sample period.
Humidity and Dewpoint
The humidity task samples the humidity sensor every minute and places the data in a buffer, averaging over a ten-minute
sliding window, and calculating the minimum and maximum humidity every sample period. Dewpoint is calculated from the humidity
and temperature data.
Barometric Pressure
The barometer task samples the air pressure sensor every minute and places the data in a buffer, averaging over a ten-minute
sliding window, and calculating the minimum and maximum air pressure every sample period.
Rainfall
The precipitation task samples the tipping-bucket rain gauge every minute and converts the number of bucket tips (0.01
inch each) into total accumulation since local midnight, and the number of bucket tips per minute as rainfall rate in inches
per hour summed over a 60-minute sliding window.
Posting Data to Weather Underground
Every ten seconds (a.k.a. " RapidFire"), the weather underground task posts the average temperature, average humidity, rainfall rate, accumulated rainfall since
midnight, the average wind speed, the maximum wind speed recorded for the previous ten seconds and the average wind direction
to Weather Underground Data Exchange.
Posting Data to Citizen Weather Observer Program (CWOP)
Every ten minutes, the CWOP task posts the average temperature, average humidity, rainfall rate, accumulated rainfall
since midnight, the average wind speed, the maximum wind speed recorded for the previous ten minutes and the average wind
direction to CWOP.
Weather Instrument Specifications
Weather Instrument Cluster
Temperature
Anemometer
Wind Vane
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Radiation Shield
To reduce solar warming effects on my thermometer/hygrometer, I built a radiation shield out of nested foil pie tins
(see figure 1, above). At this time, the pie tins are not painted, they're just natural aluminum. They started out shiny,
as pie tins do, but they have weathered down to dull aluminum, as pie tins also do.
The effectiveness of the radiation shield seems quite good. My temperature data quality typically rates " two thumbs up" from MADIS. I have some maintenance scheduled for this summer, and I might paint them with some flat white epoxy at that
time, and see how that affects accuracy.
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