Author Topic: Honey I shrunk the anemometer!  (Read 4995 times)

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Offline Skywatch

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Honey I shrunk the anemometer!
« on: October 23, 2011, 10:04:48 AM »
Last night we had a ferocious storm come through with heavy rain, high winds, and golfball sized hail. It was scary. But today I examined the weather station tower and everything seemed to be working. But one of the cups on my WMR100a broke off. I took the cup assembly off and at my work desk and changed a few things. I shortened the spokes on the cup by sawing off 1/5th of an inch, cut a little notches into the side of each cup, then hot glued the cups back to the spokes. The anemometer seems much more sensitive now to lighter winds.
I live in an apartment and for the moment am not a home weather watcher.

I am a storm chaser.

Offline Skywatch

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Re: Honey I shrunk the anemometer!
« Reply #1 on: October 23, 2011, 01:11:10 PM »
The wind readings seem higher and more consistant. I compair the WMR100's readings to that of the Vantage Pro2. Smaller cup on the OS seem to benefit the sensor's readings seems much more accurate now.
I live in an apartment and for the moment am not a home weather watcher.

I am a storm chaser.

Offline Axelvold

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Re: Honey I shrunk the anemometer!
« Reply #2 on: October 23, 2011, 02:33:48 PM »
The wind readings seem higher and more consistant. I compair the WMR100's readings to that of the Vantage Pro2. Smaller cup on the OS seem to benefit the sensor's readings seems much more accurate now.

It could be to that the spokes is shorter and that causes it to spin faster.

Personally I don't think the reading of that anemometer is accurate now when you have shorten the spokes.

Lars Magnusson
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55° 57' 41" N / 13° 6' 1" E
WX Station: Davis Vantage Pro2 Plus

Offline Skywatch

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Re: Honey I shrunk the anemometer!
« Reply #3 on: October 23, 2011, 02:48:34 PM »
The wind readings seem higher and more consistant. I compair the WMR100's readings to that of the Vantage Pro2. Smaller cup on the OS seem to benefit the sensor's readings seems much more accurate now.

It could be to that the spokes is shorter and that causes it to spin faster.

Personally I don't think the reading of that anemometer is accurate now when you have shorten the spokes.


Seems to be compaired to an anemometer (eg; Davis) that's gone through accuracy tests. It's pretty self explainatory. When the cup assembly was wider required alot more torque to get it moving constant. http://www.wxforum.net/index.php?topic=13272.0 Here's a thread to a question I posted about a week ago about anemometer design to accuracy.
« Last Edit: October 23, 2011, 02:51:19 PM by mckTXaws »
I live in an apartment and for the moment am not a home weather watcher.

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Offline Skywatch

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Re: Honey I shrunk the anemometer!
« Reply #4 on: October 23, 2011, 02:58:00 PM »
The Davis and OS anemometers are located together. The Davis has not changed in design but the WMR100 wind sensor has. Using the Davis as the independent variable and the WMR100 as the controlled variable to get an consensus of accuracy. The Davis anemometer's accuracy information is provided the WMR100 varies. I have found the accuracy because both wind measurements correlate better now than used to. I conclude accuracy has been improved to match that of the Davis.
I live in an apartment and for the moment am not a home weather watcher.

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Offline Skywatch

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Re: Honey I shrunk the anemometer!
« Reply #5 on: October 24, 2011, 08:48:56 PM »
It's official the WMR100's new cup revision improved it's accuracy. What I saw today?
Higher winds that compair to a local regional airport.
Winds that compair to surroungind stations +/- 0.2 mph.
Reading of wind even durring calm conditions reported by other stations.

The new design is much better.
I live in an apartment and for the moment am not a home weather watcher.

I am a storm chaser.

Offline xykotik

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Re: Honey I shrunk the anemometer!
« Reply #6 on: October 24, 2011, 09:31:15 PM »
Ask wxtech Al if he can add that to the anny calibration guide.

That's one of those obvious mods you don't think of, like "speed holes."
http://www.youtube.com/watch?v=XVV_COOey0E


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Offline Skywatch

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Re: Honey I shrunk the anemometer!
« Reply #7 on: October 24, 2011, 09:46:10 PM »
Okay, thank you. I forgot about that thread. Good idea.
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Offline JACK10562

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Re: Honey I shrunk the anemometer!
« Reply #8 on: October 24, 2011, 10:22:32 PM »
Your readings are going to be higher with the now shortened spokes due to the wind vane circumference is smaller, the distance traveled per revolution is less.

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Offline paleoguy

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Re: Honey I shrunk the anemometer!
« Reply #9 on: October 25, 2011, 05:48:46 AM »
Hm-m-m-m, a puzzle to me.  I would think that the shorter arms would result in higher rpm's with a given wind, once a wind speed threshold was reached.  But, it should also result in less sensitivity to lower winds speeds or overcoming at-rest inertia due to a reduction in mechanical leverage caused by the shorter arms.  If your mod is more accurate, perhaps the original design was off a bit.
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Offline Skywatch

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Re: Honey I shrunk the anemometer!
« Reply #10 on: October 25, 2011, 12:04:10 PM »
Confused? It maybe harder for someone who hasn't observed for them selves than for someone who has and is getting their info from personal experience. The cups being closer to the hub means it takes less wind because one cup is pushed the distance to move another cup in position. Before the cups had to travel further and usually they didn't in light wind conditions. Now do you see why this new design is better? Especially when compared to a Vantage Pro2 and a WS1910U-IT, I have 2 references to tell me my theory is correct on what's observed through out a wind period.
I live in an apartment and for the moment am not a home weather watcher.

I am a storm chaser.

Offline Scalphunter

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Re: Honey I shrunk the anemometer!
« Reply #11 on: October 26, 2011, 10:13:52 PM »
 If your theroy right then change the tires on your car  to an smaller size and see what the difference is.  Every thing travels  one rpm but the differents id the distance it travels during that rpm.

Offline xykotik

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Re: Honey I shrunk the anemometer!
« Reply #12 on: October 26, 2011, 10:43:59 PM »
Your readings are going to be higher with the now shortened spokes due to the wind vane circumference is smaller, the distance traveled per revolution is less.

The wheel-speedometer example is not a good analog to an annemometer for a couple of reasons....

It is true that putting a smaller than specified circumference tire on a vehicle will increase the inaccuracy of the speed measurement, but putting a wider tread (analogous to larger windcups on shorter/longer arms) on the diminished-circumference tire will not compensate.  Direct contact with the road turns the tire/wheel/speedometer and increasing friction or drag (eg, by leaving the parking brake engaged) will not change the relationship between the wheel and the road unless it is completely locked up and skidding.  It is always a 1:1  relationship to contact.  Only the formula used to translate a rotation count to speed can compensate for the radius (vis circumference) change.

An anemometer on the other hand has various factors contributing to torque and drag, and therefore the acceleration and spin of the unit relative to actual wind-speed.  Those can include length of those cup-arms (eg wheel diameter), size of the cups, shape of the cups, drag of bearings, etc.  Changing any of those could have a measurable effect that could only be accurately measured with a fixed wind source.  I'm sure a lot of thought goes into the design of an anny such as
x rpm=x mph using a look-up table, which wxtech's anny knowledgebase thread seems to indicate. 

In it's most basic form, a big sail catches more wind and moves a boat faster than a little sail, but the wind still makes it billow if the boat is anchored and not moving.    The road doesn't cease to move by a rotating wheel at any rate other than they always make contact, unless it is skidding.

(sorry if confusing, I just see the wheel/speedo analogy as apples and oranges)

I say if your mod provides a more accurate reading by your observation as compared to what you consider a trusted standard, then great!  I know you will watch it at various speeds to see if it tracks.


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Offline DanS

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Re: Honey I shrunk the anemometer!
« Reply #13 on: October 26, 2011, 11:36:34 PM »
How 'bout this analogy, your open hand only (wind cup) sticking out a car window going 60 mph. Then your whole arm with open hand (same cup size with arm mount now) sticking out a car window going 60mph. Longer reach = more wind/mechanical leverage I believe paleoguy was referring to?.?.
« Last Edit: October 26, 2011, 11:41:09 PM by DanS »

Offline SlowModem

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Re: Honey I shrunk the anemometer!
« Reply #14 on: October 26, 2011, 11:43:33 PM »
Then your whole arm with hand sticking out a car window going 60mph.

That's how I play the harmonica!   =D>
Greg Whitehead
Ten Mile, TN USA

Offline DanS

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Re: Honey I shrunk the anemometer!
« Reply #15 on: October 26, 2011, 11:51:19 PM »
Then your whole arm with hand sticking out a car window going 60mph.

That's how I play the harmonica!   =D>

lol...60mph=G
      35mph=C
      18mph=D
      ...

edit: and approx. 28 gallons to play Inna Godda Davida.
« Last Edit: October 27, 2011, 12:01:50 AM by DanS »

Offline SlowModem

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Re: Honey I shrunk the anemometer!
« Reply #16 on: October 27, 2011, 12:46:52 AM »
edit: and approx. 28 gallons to play Inna Godda Davida.

YMMV!   :lol:
Greg Whitehead
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Offline Scalphunter

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Re: Honey I shrunk the anemometer!
« Reply #17 on: October 27, 2011, 01:37:33 AM »
 What is it that everytime I writesomething in this form I am tpld it is  wrong. Maybe I should take my knowledge and XP and just get lost and make all you gossuk happy.

 With that I have nothing more to say.

Offline DanS

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Re: Honey I shrunk the anemometer!
« Reply #18 on: October 27, 2011, 06:04:21 AM »
What is it that everytime I writesomething in this form I am tpld it is  wrong. Maybe I should take my knowledge and XP and just get lost and make all you gossuk happy.

 With that I have nothing more to say.

I believe it's just another one of those times where the meaning of a post gets lost or jumbled when put in text form and read differently than it's intent. Your wheel size reduction resulting in increased speed readings made sense to me but others may have read it differently. Hang with us John and please don't take it personally. I for one would like to continue 'seeing' you around and hear your valued input or just gabbing with you. ;)

Dan
« Last Edit: October 27, 2011, 06:11:26 AM by DanS »

Offline xykotik

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Re: Honey I shrunk the anemometer!
« Reply #19 on: October 27, 2011, 10:23:04 AM »
What is it that everytime I writesomething in this form I am tpld it is  wrong. Maybe I should take my knowledge and XP and just get lost and make all you gossuk happy.

 With that I have nothing more to say.

I read everything again, and I don't see anyone saying you are wrong.  I see discussion about comparisons, but offering alternatives or questioning an analogous comparison isn't a personal attack.  When I logged in this morning, I wondered in what way you might think my part in the discussion was somehow a negative criticism of you personally, even though I was careful to quote someone else's post hoping you wouldn't assume that since I was posting after you that it was directed towrd you.  It seems you are offended anyway.  You own that chip on your shoulder, so it's pointless to continue tiptoeing around eggshells any longer in hopes of sparing your feelings.  You own those too.  At least this time you didn't impune my (assumed) ethnic heritage or question my patriotism.  I think that shows great progress and I look forward to further civil interactions. 

Your experience and regional perspective are greatly valued here, by me and others.


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Springtime in Seattle...  March comes in like a lion and out like a wet lion.

 

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