Cumulus Support

My Oregon WMR968 wind speed has always shown wind speed values too low to believe. All of the other instruments seem very accurate.

I decided that the cause must be that it was not up high enough, so I put it up much higher.

It is now about 35 feet above the ground, and about 5 feet above the roof peak. There are trees taller than the house starting about 100 feet from the house, but most all of them have no leaves this time of year. There are no buildings in front or back of my house. The building to the south is shorter than mine (about 150 feet away), and the building to the north is 150 feet away and is the same height as mine.

When I moved the instrument to this high point, I got a slight increase in wind speed, butt I knew it was still very wrong.

I could raise it up about 2 more feet, but I doubt that it would make a difference.

I have now set the "Wind Speed" and "Wind Gust" calibrations both to 1.80. I used observations from several nearby stations as well as my own observations of the local tree sway to come up with the 1.8 number. I am now convinced that my readings are puls or minus 20%.

Is there anything I can do to better my accuracy?

Ken
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Hi Ken,

After the obvious "electro-mechanical" checks (for stiff bearings or mis-generated/detected revolution pulses, etc.) you should be able to calculate the calibration to within about +/- 20% assuming an "anemometer factor" of 2.75 (i.e. wind speed / cup speed).

If you don't have access to a calibrated wind tunnel and can't borrow a precision calibrated anemometer to run alongside yours, then attaching the anemometer to a moving vehicle may be the only practical way. But it needs a tall mast above the roof (or better, a long mast pointing ahead of the hood) of the car, a GPS to check the (probably "optimistic") speedometer, ideally a helper and a still day, etc. for a satisfactory conclusion.

Cheers, Alan.

This calibration would be worth doing just to see the looks you get from passersby!