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Meteorologica

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    Morecambe, UK

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  1. If only that was true! Many sensors at official stations are out of calibration. Then of course there is the definition of how you officially measure wind speed and it is definetly not an instantaneous measurement, the official WMO specification is for it to be the average sampled over 2 minutes for land based stations. What most people see as the wind speed is actually the fastest recorded speed over a small sample period but sadly thats not anything like the official standard. The big difference between airport measurements and home measurements is the site location of the anemometer. On an airfield its mounted clear of any buildings so there is a planar air flow over the instrument producing a much more consistent speed measurement. In a domestic situation the anemometer tends to be mounted above the roof of a building and even though it is exposed to the wind without any obvious obstructions, the apparent sureface layer that the wind blows over is extremely bumpy due to the buildings in an urban environment. These "bumps" produce frictional drag and hence turbulant wind thus making the home based anemometer having to read the wind speed from a very turbulent wind stream.
  2. As we understand it, it takes a sample over 11 seconds, which is much better than the 128 seconds of the LaCrosse and even the 14 seconds of the WMR928. Then, every 33 seconds it sends the highest of the last three 11 second samples.
  3. We have a huge range of them http://www.meteorologica.co.uk/prodtype.asp?PT_ID=95
  4. You also need to be aware that the WMR928 has a wind sampling period of 14 seconds. Basically this means that it counts the anemometer revolutions in the 14 seconds and works out the average speed for the 14 seconds. Professional anemometers sample every 2 to 3 seconds so they are much more likely to see higher gust speeds. The rule is that the longer the sampling period the lower the maximum gust recorded will be. We have a WMR928 anemometer mounted alongside a Davis that samples every 2.5 seconds and on gusty days the WMR928 undereads by some 25% compared to the Davis. This, however, is not bad when compared to devices like the LaCrosse WS2300 that in wireless mode samples every 128 seconds unless its very windy where upon it samples every 32 seconds. This of course means the peaks are rounded out even more! You should also make sure that you have grounded your anemometer as this is a requirement for the WMR928 to make sure it works correctly and prevents static buildup on the electronics. If you haven't grounded it then this might also explain your weirdly consistent readings.
  5. The WMR918 is an older version of the current model which is a WMR928NX, it has lower power solar panels on its transmitters. As for fixings, you can buy poles from B+Q Warehouse. They sell them and brackets for TV use and they will do fine for a weather station. Location for the sensors is: Rain gauge, on a flat surface as far away from tall, surrounding objects as possible to prevent a "rain shadow" when the wind is blowing. Thermometer, in the shade at all times. Also it needs to be away from any heat sources such as a wooden fence that may warm up on the other side and then reradiate heat. Anemometer, as clear as you can from any nearby tall objects that will shelter it from the wind. Usually this means on a pole well above the roof line of the house. Often a local aerial installer will put this up for you.
  6. Don't know about WD but Virtual Weather Station has its own wizard for creating web pages from your weather data and it can then automatically upload them to your website.
  7. Both Lightning 2000 and NexStorm will allow you to upload images to the web.
  8. The 928 is a far superior weather station to the 3600. It also has a much better wind sampling period than the 3600 does in wireless mode which means it will record gusts far better.
  9. The WS3600 uses a fairly non standard way to communicate with the PC over the serial port and many usrs have discovered that most USB to serial converters don't work with this model.
  10. If you have an Oregon Scientific anemometer then it is a requirement that you earth it, they even have a tag on the end of the anemometer's arm just for this purpose. The anemometer is very susceptible to static buildup and it will simply stop working at some point needing a reset to get it going again if you don't earth it. This isn't lightning protection just a way to drain away any static charges it collects.
  11. For £150 you are limited in your choice if it has to connect to a PC and the LaCrosse models are probably the only ones available to you. The WS2300 with its potential problems is still not a bad buy for the money especially if you run it in wired mode rather than wireless as this changes the sample rate to 8 seconds from the 32 or 128 second sample on wireless (depends on wind speed)
  12. This is a common problem with the LaCrosse units. Basically the wire between all the sensors can act as an aerial and introduce noise into the system. The only way to fix it is to either replace the cable with screened or add some small capacitors onto the circuit boards. The wind speed underreads gusts because of the sampling rate. All electronic anemometers count the number of revolutions of the anemometer in the sampling period and then calculate the speed from that. So, if during the sample period a sudden gust blows the anemometer simply sees it as a small increase in the average speed over the sample period. THis is why the LaCrosse units in wireless mode always underead. We run a Davis (2.5 second sample) alongside an Oregon (14 second sample) and the Oregon always undereads gusts by 25% compared to the Davis.
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