How are the Holfuy weather stations measuring and processing the wind speed
Wind speed is a weather quantity caused by air moving from high to low pressure areas. There are many practices and methods to measure the wind speed values. In this chapter we describe, how Holfuy products are calculating and handling the wind speed data.
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In every N-th second a Holfuy station stores an "actual" wind speed sample in its internal memory. For the mechanical wind sensors 'N' is 3 seconds. And the sampling means counting the total number of rotations of the cups during the whole last 3 seconds, then calculate the average wind speed with the formula of the wind sensor. E.g. for the Davis 6410 wind sensor this formula is: 1600 rev/hr = 1 mph. For ultrasonic wind sensors the N is between ~2-10 seconds, and the samples are more like instantaneous wind speed readings.
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When it's time to report the weather data to the servers about the last measurement interval 'M' (2 minutes by default). There will be many (M/N) wind speed samples stored in the station's internal memory. From these the station calculates the following values:
- Average wind speed: The average value of the samples.
- Gust/maximum wind speed: The maximum value of the samples.
- Minimum wind speed: The minimum value of the samples.
E.g. if there are 10 samples and the samples are 3,4,1,0,2,4,6,9,8,6 the reported average wind speed will be 4.3 -> 4km/h, the maximum gust 9km/h and the minimum 0km/h.
Note:If the reported gust >= 40km/h and the gust >= the double of the reported average wind speed, then the system will dampen the gust to the average wind speed + 10km/h (to filter out irrational wind gusts). - The station uploads only these three values for the wind speed, together with other measurements like air temperature in a weather data packet. At the same time the internal wind speed samples from the last measurement interval will be deleted, and a new measurement cycle starts.
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The quarter hourly and hourly average tables are showing the average wind speeds and maximum wind gusts from the weather station. These are calculated by the server from the incoming weather data packets from the last one (quarter) hour long interval before the average's timestamp. E.g.: The displayed quarter hourly average wind speed for the 14:00 timestamp is the average of the reported average wind speeds between 13:45 and 14:00.
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