I think that anemometers are an interesting topic but it appears this one
has been beat to death and I'm not sure why this is even a topic for TT. Is
it because it is attached to a ham radio tower? If so maybe we need to
discuss the "ins and outs" of the flag I hang on my tower on 4th of July.
(Incidentally I have an anemometer on my tower too.)
I haven't gotten any raunchy pictures yet from TT but this will be my test.
Bill W5VX
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of GARY
HUBER
Sent: Wednesday, April 30, 2014 5:17 PM
To: k1ttt@arrl.net; TT TowerTalk
Subject: Re: [TowerTalk] Wired Anemometer for Tower?
The fans at
http://en.wikipedia.org/wiki/File:Twin_Groves_Wind_Farm_DSC03252.JPG --- 85
foot blades on 270 foot tower.
-----Original Message-----
From: GARY HUBER
Sent: Wednesday, April 30, 2014 12:54 PM
To: k1ttt@arrl.net ; TT TowerTalk
Subject: Re: [TowerTalk] Wired Anemometer for Tower?
I really have a problem with the big fans, several hundred locally, that
blow almost constantly around EN50nj. (tongue firmly in cheek)
73 & DX,
Gary - AB9M
-----Original Message-----
From: David Robbins
Sent: Wednesday, April 30, 2014 7:11 AM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Wired Anemometer for Tower?
and accuracy compared to what, and over what period?? wind speed is HIGHLY
variable over small distances and elevation change. There are
specifications for measuring wind that require so much open area, a specific
height above terrain(much lower than you would think), distance from
buildings, etc... basically measuring wind speed on a tower is only
interesting for you and your antennas, no one else would have any use for
it. take a look at my station's quality control charts...
http://weather.gladstonefamily.net/qchart/AR841?date=20140428 you will see
that normally things like temperature and barometric pressure track the
expected values pretty well... but my wind speed, when I just looked at
yesterday's values, were off by a factor of about 10 (my reading is higher!)
from the expected values. this is because my anemometer is 50' up and not
far enough from the house, and my house is almost 1000' above the nearest
airports or nws offices. and yet when measuring gusts usi ng skywarn tree
motion estimates or a handheld pith ball pressure gauge it usually reads low
by a factor of 2 (a gust estimated at 50-60mph only reads 25-30mph on the
anemometer). part of that is the response time, but most is probably the
averaging over 3 to 5 seconds that I think the davis uses. I tried at one
time to look up the specs for reading gusts, it gets very confusing even on
the noaa web site, there are at least 3 different specs (that I found) for
different instruments that use 3, 5, or 8 second gust averaging. If you
really want an eye opener about wind and height above ground come up my 180'
tower some day, it can be dead calm on the ground, and even at the 50'
elevation of the anemometer, but still have a nice 5-10mph breeze at the
top... nice for me, but tough for the ground crew fighting black flies,
mosquitoes, and deer flies.
Apr 30, 2014 07:40:14 AM, K8RI-on-TowerTalk@tm.net wrote:
On 4/29/2014 9:59 PM, Jim Lux wrote:
On 4/29/14, 5:08 PM, Al Kozakiewicz wrote:
I'm not going to belabor the point. Wind speed is derived by
measuring the change in rotational position divided by time. The
shorter the sampling interval (time), the lower the measurement
accuracy. There is no reason for this to controversial.
Just count the pulses, and divide by time. Plastic anometers have very
little rotational mass.
With out getting fancy you can easily get better than 1 mph accuracy.
To me, more than every three seconds is wasted energy/effort/money/time as
is all the effort expended to measure errors that are meaningless unless you
want lab accuracy for a study. Then calibration becomes a major portion of
the effort. Then you need standards traceable to the NBS and someone
certified to do it. Been there and done that, but not with anemometers.
73
Roger (K8RI)
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