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4/13/20 Rain/Wind/Thunder obs/disc


Torch Tiger
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Just now, ORH_wxman said:

Getting a bit worried here...really starting to crank and the woods behind my house are to the south....those tall trees would want to fall right towards the house in a southerly wind event.

Get the fam away from that area. I'm sure you know though.

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31 minutes ago, dendrite said:

It’s tough to get a near instantaneous mechanical sensor since you need to get a specific number of revolutions per given time to determine a speed. There’s just not enough rev samples if you try to cut it down to under a second. Now they could be using a 3rd party ultrasonic sensor that would have instantaneous capability, but my assumption was that they had the cups. Here’s Davis’ speed equation calculation...

F500DEB8-8B23-4826-AB8D-9D73449AAB67.jpeg

Or do it the old fashioned way with a motor that generates a voltage relative to the speed. Thought some of the earlier Davis stations worked this way hence their caution of extending the wind cable beyond 40 feet because the loss of voltage would cause the speed to be lower than measured.

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14 minutes ago, snowman21 said:

Or do it the old fashioned way with a motor that generates a voltage relative to the speed. Thought some of the earlier Davis stations worked this way hence their caution of extending the wind cable beyond 40 feet because the loss of voltage would cause the speed to be lower than measured.

The drop in voltage only affects the maximum possible recordable wind speed. IIRC, the max is around 175mph at 150ft but drops to under 140mph at about 250ft. They have large and small wind cups too which have different accuracies and max capabilities at different speeds and cable lengths.

Just found this...

https://www.novalynx.com/manuals/WRM_apnote15.pdf

Most of the Davis stations now have an integrated sensor suite or wireless anemometer transmitter so lengths are generally 40ft or less.

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