Regardless of the specific instrument, ANY digital measurement system will
require some amount of time to sample the transducer output. The time required
depends on the resolution of the transducer, stability of the reference
timebase and the measurement accuracy required.
You're calculating windspeed from rotational velocity. The latter is probably
measured using either an optical sensor or some electromagnetic device. In
either case, you're counting pulses over a specific period of time to get a
large enough sample to outweigh the measurement uncertainty, which increases as
the sample time drops as well as with decreased encoder resolution.
I have no first hand knowledge of converting anemometer RPM's to windspeed, but
if the relationship isn't linear, you have the additional step of a table
lookup or curve fit to convert the rotational speed to wind speed for display.
Al
AB2ZY
________________________________________
From: TowerTalk [towertalk-bounces@contesting.com] On Behalf Of tomkd8deg
[kd8deg@centurytel.net]
Sent: Sunday, April 27, 2014 11:29 PM
To: 'Kim Elmore'
Cc: 'EZ Rhino'; towertalk@contesting.com
Subject: Re: [TowerTalk] Wired Anemometer for Tower?
The unit I have is the Davis Vantage Pro2 wired, and the 4 second delay is what
Davis tech support told me when I questioned the accuracy of the wind readings
that were being displayed.
Tom KD8DEG
From: Kim Elmore [mailto:cw_de_n5op@sbcglobal.net]
Sent: Sunday, April 27, 2014 8:08 PM
To: tomkd8deg
Cc: EZ Rhino; <towertalk@contesting.com>
Subject: Re: [TowerTalk] Wired Anemometer for Tower?
I'm not sure that's true about the wind. I have a Davis Vantage Vue. The remote
unit does some processing to generate a 2 s mean speed and a peak gust value
within the 2 s window. Data are then sent in packets every 2 s to the base unit.
Mine is up 10 m (a WMO standard height). During calm winters nights it will
measure an anomalously high minimum temperature. The anemometer is shielded a
bit by the tower structure when it's downwind of the tower and so the wind
speed is biased low. Direction appears unaffected.
The rain gauge is a tipping spoon with a 3" diameter catchment. It under
samples only at high rain rates. The temperature sensor and dew cell are not
aspirated in this unit and so temperature is biased a bit high due to radiation
errors on calm, clear Summer days.
I highly recommend any of the Davis units, but the Peet Bros. Ultimeter 2100 is
also a very fine unit. Both are comparable in price (~$400).
Kim N5OP
"People that make music together cannot be enemies, at least as long as the
music lasts." -- Paul Hindemith
On Apr 27, 2014, at 18:29, "tomkd8deg" <kd8deg@centurytel.net> wrote:
The Davis wired version, which I am using, has a 4 second delay for wind,
and direction display. That can mean the loss of 10 to 20 mph in a gust
situation.
Tom KD8DEG
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of EZ
Rhino
Sent: Sunday, April 27, 2014 4:10 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Wired Anemometer for Tower?
I should mention one other thing about the "cheap" weather station
anemometers that drive me crazy. The first WX station I had only updated
the wind speed about every minute. The LaCrosse updates about every 12
seconds. This is almost worthless...I want to know the wind speed NOW! The
stuff from Inspeed is real time, very nice.
Chris
KF7P
On Apr 27, 2014, at 14:03 , Roger (K8RI) on TT wrote:
On 4/27/2014 3:15 PM, EZ Rhino wrote:
I have tried a few different weather stations, so I can unequivocally tell
you what NOT to get.
DON'T buy anything under $300. *sigh*
Mine cost 40 something, works fine, is made of cheap plastic. Uses plain old
Duracell non rechargeable. Last 2 years or more outside. The ones indoors
only last 6 mo to a year. Probably cost twice that much now...if available
Mounted on the tower where I can just reach it with an 8' stepladder.
Does nothing except report wind speed, direction,temp, humidity, and
relative temp.
73
Roger(K8RI)
Unfortunately the cheap ones are total garbage. The recent one I got is a
LaCrosse station, purchased from Costco. Junk! Junky cheap plastic, the
rechargeable batteries in the solar powered wireless anenmometer/wind vane
unit went bad in the first year, and the rain bucket stopped working in the
first few months after purchase.
The Davis units are good, have a buddy with one and it is quality stuff.
And about $300. You pay for what you get. I agree, I think the wired units
are more reliable and last longer.
Ok now take a look here: www.inspeed.com These guys make anemometers
that are decent quality and not expensive. They also have a cool computer
hookup version that allows your PC to track all the data and put it in a
spreadsheet. AND it has the wind switch option, where you can program the
system to turn an appliance on or off (read: lower your tower!) if the wind
goes above a preprogrammed speed. Pretty neat. I don't have this option
yet. I think AB7E has one of the inspeed units too, maybe he can provide
some feedback.
Chris
KF7P
On Apr 27, 2014, at 11:01 , Steve Jones wrote:
Can any of you recommend a wired anemometer or weather station unit?
I want to install an anemometer to monitor the wind speed at the top
of my tower. All I can find online are wireless units. On this
reflector I have seen a number of bad reviews of wireless weather
sensors, because their little wifi transceivers get damaged by the RF
from a ham antenna. I have a spare CAT5 cable at the base of the tower
available.
73,
Steve
N6SJ
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