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Weather Station Hardware => Other Weather Station Hardware => Topic started by: L5n25 on January 01, 2009, 06:17:53 PM
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Do folk find a need to "calibrate" their anemometers? So as to add appropriate offsets in their weather station software?
If so, what is your approach to doing so?
My lot is somewhat sheltered by a high number of fir trees but otherwise seems to be somewhat open at the height of the sensors; does that mean that my wind speeds are always suspect?
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The wind speed is what it is for your location. If your lot is sheltered by trees or the like, then what ever the wind speed is, it is. What could you even possibly adjust it against? The wind speed at the local, wide open airport?
One thing you have to keep in mind. Your weather reading are the readings for YOUR location, not a location 10 miles down the road.
I wouldn't adjust a thing.
Bob
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Bob I think he was asking if you can calibrate your anny. You know, like how you can adjust the screws on the Davis rain gauge to get a more accurate reading.
I don't think you can calibrate the anemometer. At least I have never heard of anyone doing it. I would imagine any calibration is done at the factory.
As for your location, yes your reading will always be suspect with trees around. Don't worry though, most of us are surrounded by trees. There's not much you can do about that.
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Yeah, I guess that could be what he is asking about. I dunno. Just read his post again and my brain still sees the same thing. :oops:
Bob
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Regarding wind speed, I agree with Bob on not setting a gain. We like to think that our station is more accurate if it agrees closely with the nearest official station. Also, we feel disappointed if our high wind isn't as high as that at the nearest official station or as high as that reported by the TV mets. It sounds more impressive to say "50mph" than "35mph".
However, like yours, my neighborhood is laden with big ol' trees of all sorts, but I want my station to represent what's truly going on in my neighborhood with all its trees, so I don't set a gain. There are some PWS owners here who set a gain on their wind speed, and it is your station so you certainly should do as you wish. As Bob said, though, how does one know what the correct gain would be? (and compared to what?)
Just another opinion. :grin:
Regards,
Kevin...
EDIT: By the way, welcome to the forum!
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One thing you have to keep in mind. Your weather reading are the readings for YOUR location, not a location 10 miles down the road.
This is true, *but* if I'm broadcasting this info on a website, I want as broad an an audience as possible and want this info to have meaning to my viewers.
What good is a website that says, "Even though it's blowing 50mph across the street, the "true" windspeed is 20mph because my equipment happens to be located in a less than optimal location"
In this case, I can see the desire to calibrate a gain. Fortunately for me, I'm in the desert and obstructions are not an issue.
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The wind speed is what it is for your location. If your lot is sheltered by trees or the like, then what ever the wind speed is, it is. What could you even possibly adjust it against? The wind speed at the local, wide open airport?
One thing you have to keep in mind. Your weather reading are the readings for YOUR location, not a location 10 miles down the road.
I wouldn't adjust a thing.
Bob
Thanks. Indeed I had thought of that... the wide open airport, even though I'm a mere 3 miles away, is always going to have "uninterrupted access" to the wind; but that's not what is going on at my place -- by definition. :-) You definitely answered part of my question here... did people feel a need to enter an offset and compared to what?
Another way to look at it though is if I had a mast tall enough to raise the sensor 10 feet above my trees (tall order since they are probably 70 years old and probably a good 90 feet tall) I could sample the wind at something closer to my local "unobstructed norm". But short of actually erecting such a huge tower, I can't determine that.
The other less obvious question though was... even at the airport... there's factory calibration but is there a need to calibrate it again perhaps later when the bushings become slightly worn... or do they just go out and buy a new sensor every couple of years? How would they independently know the speed and thus become alerted to the fact that the sensor was out of whack? I partially have an answer for that... since they have a windsock and the windsock will only "fully extend" at about 15 knots they could use that to "back calibrate".
Lacking a windsock though I'm not sure how one could determine the accuracy of the anemometer.
Apologies for not being explicit in my question(s); perhaps I should of sorted out my questions more specifically.
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<snip>
As for your location, yes your reading will always be suspect with trees around. Don't worry though, most of us are surrounded by trees. There's not much you can do about that.
So in Weather Display one can apply an offset to the values you receive from your station; so, if I knew an "appropriate" offset somehow I could adjust it much like I do with my barometric values by using a barometric altimeter on my handheld GPS to effectively back correct my "station pressure" to the sea level equivalent that I then report to my PWS on Wunderground.
The trick though would be knowing what offset to apply for my location. Short of erecting a 100 foot mast to raise my sensor above the tree tops though, I'm not sure there's anything I can do.
Of course I'm partially content to just report what it reads 10 feet off the ground too. ;)
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One thing you have to keep in mind. Your weather reading are the readings for YOUR location, not a location 10 miles down the road.
This is true, *but* if I'm broadcasting this info on a website, I want as broad an an audience as possible and want this info to have meaning to my viewers.
What good is a website that says, "Even though it's blowing 50mph across the street, the "true" windspeed is 20mph because my equipment happens to be located in a less than optimal location"
<snip>
Yes, so today in Beaverton OR a bunch of PWSs on Wunderground were reporting winds SSW at 10 to 15 mph whereas mine was reporting SSW at 6 mph. Of course a number of them were also reporting 5 mph as well. Mine is a newly created station and I'd like it to be as accurate as I can make it; so that's why the question occurred to me.
One thing that occurred to me is I could take my battery powered console and sensor to the airport and sample the wind there under the same conditions and thus see what the delta from my instrument might be, assuming of course that the airport's is accurate ;-)
Thanks for your response.
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This is a pain to do, and perhaps one day I will do it. But I picked it up from the old forums.
On a "wind calm day". Run your station in battery mode, grab your anemometer and attach it about 10 feet above the roof of a pickup truck(to clear air disturbances from the vehicle. Take a reading on the wind speed and vehicle speed at 5 or so "predetermined speeds"like at 10,20,30,40,50. Notice any difference for each, write those numbers down, then average out the differences. Take the "average difference" and add(If a positive number) or subtract (If a negative number) that to your middle number (30 in this example) here.
Then take the "new" number (we will say 30+4 for a wind speed that reads too fast) and divide that by the 30.
So 30+Your diff of 4/30=
34/30=1.33 your new gain.
If your "average difference" happens to be a negative number (3 for this second example) then you subtract..
30-Your diff of 3/30=
27/30= 0.90 your new gain.
As far as obstructions like trees and such. That is a different story.
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This site says they calibrate Davis instruments.
http://www.microprecision.com/capabilities/anemometer_calibration.php
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The vehicle method sounds like an AFV clip in the making to me. #-o :oops:
(http://farm1.static.flickr.com/21/33938725_f0a289c841_m.jpg)
Bear in mind that the vehicle method will only give a correction for a poorly calibrated anemometer (say one that is wearing out). It cannot be used to compensate for low wind readings due to trees.
Bear in mind, too, that with this method you're now adding the uncertainty of the car's speedometer. So I wouldn't take readings at any speed below 20mph (too much uncertainty). There's also too much uncertainty with a standard dial/needle speedometer. (There's even uncertainty with a digital speedometer.)
Has anyone ever used this method?
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The vehicle method sounds like an AFV clip in the making to me. #-o :oops:
(http://farm1.static.flickr.com/21/33938725_f0a289c841_m.jpg)
Bear in mind that the vehicle method will only give a correction for a poorly calibrated anemometer (say one that is wearing out). It cannot be used to compensate for low wind readings due to trees.
Bear in mind, too, that with this method you're now adding the uncertainty of the car's speedometer. So I wouldn't take readings at any speed below 20mph (too much uncertainty). There's also too much uncertainty with a standard dial/needle speedometer. (There's even uncertainty with a digital speedometer.)
Has anyone ever used this method?
I was just throwing it out there. But I use a GPS to calibrate my speedometer on the fly, and it's dead on. :-)
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I was just throwing it out there. But I use a GPS to calibrate my speedometer on the fly, and it's dead on. :-)
Just joshing, Sam. I just couldn't pass up the opportunity to get a laugh. ;)
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My car speedo is off 7%. As soon as I got it. I wondered why I kept getting flashed in the fast lane. Measured with two gps's, even paced my wife's one day. Dealer said that was "normal", anything under 10% as long as its on the low end. That was not the answer i was looking for.... but they wouldnt/couldnt adjust it.
You could get one of those hand held numbers, like Geraldo used during the galveston hurricane....
Andrew
I was just throwing it out there. But I use a GPS to calibrate my speedometer on the fly, and it's dead on. :-)
Just joshing, Sam. I just couldn't pass up the opportunity to get a laugh. ;)
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The vehicle method sounds like an AFV clip in the making to me. #-o :oops:
Bear in mind, too, that with this method you're now adding the uncertainty of the car's speedometer. So I wouldn't take readings at any speed below 20mph (too much uncertainty). There's also too much uncertainty with a standard dial/needle speedometer. (There's even uncertainty with a digital speedometer.)
Has anyone ever used this method?
Of course! I use this method to play the harmonica. It's louder at 60 than it is at 20. And sometimes in the summer the bugs kind of stop up the holes. :lol:
I wonder if a hand-held wind sensor would get a person out of a ticket? \:D/
".....but Officer, I was only going 30! Look at this wind speed!"
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My car speedo is off 7%.
That can't be a pretty sight! :shock:
I wondered why I kept getting flashed in the fast lane.
Maybe switch to boxers?
:lol:
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Our local police department strategically places a handy little device like the one pictured below around town to help us check our speedometers. ;)
(http://img.photobucket.com/albums/v176/memmurphy/radar.jpg)
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I literally LOL'd when I read this.
Andrew
My car speedo is off 7%.
That can't be a pretty sight! :shock:
I wondered why I kept getting flashed in the fast lane.
Maybe switch to boxers?
:lol:
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Our local police department strategically places a handy little device like the one pictured below around town to help us check our speedometers. ;)
(http://img.photobucket.com/albums/v176/memmurphy/radar.jpg)
Don't ya just love'em! ;)
Our town got one, named it "Buster" and placed it into action. Within 2 days, its name was changed to "Blaze". Someone torched it to the ground. Got it repaired/replaced and it only lasted a week this time. Needless to say, "Blaze" is parked in the town garage now. #-o
Bob
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I hate it when you're driving in unfamiliar territory. You come over a hill and waiting at the bottom is the edge of a small town. There's "blaze" telling you that you're going 45 in a 25mph zone. #-o
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The vehicle method sounds like an AFV clip in the making to me. #-o :oops:
Sam will be starring in next season's StormChasers series driving the PIV...Pavement Intercept Vehicle...followed by the PERV...Progressive Emerg Response Vehicle.
I had to.
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<snip>
I was just throwing it out there. But I use a GPS to calibrate my speedometer on the fly, and it's dead on. :-)
re. the "tall pole in the pickup truck method". LOL. Thanks! An "interesting" idea! :lol:
I too have "calibrated" my car's speedometer via the GPS... it's pretty close at highway speeds... probably half a mph fast. GPS is a handy little gadget to have around! :grin:
I'm beginning to think that my idea of taking my sensor and console to the airport one day might not be a bad idea. I have the local airport's "ATIS" number that reports the wind speed "on the 53" of each hour. I'll just drive there at 10 til the hour, stick the unit into the wind and see how it compares. That will be one variable out of the equation!
Donald.
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I'm beginning to think that my idea of taking my sensor and console to the airport one day might not be a bad idea. I have the local airport's "ATIS" number that reports the wind speed "on the 53" of each hour. I'll just drive there at 10 til the hour, stick the unit into the wind and see how it compares. That will be one variable out of the equation!
Donald.
Just keep an eye out for airport security and the air marshalls, both of whom might give you second looks, 8-) especially if Andrew (mackbig) also shows up with his car speedo 7% off. :shock: :oops:
:lol:
(Sorry, Andrew. I couldn't pass up another opportunity. But I'm glad you enjoyed the first one. :grin: Hey Andrew...got any C-u-r-t-a-s for sale? [-o< :mrgreen:)
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My car speedo is off 7%. As soon as I got it. I wondered why I kept getting flashed in the fast lane. Measured with two gps's, even paced my wife's one day. Dealer said that was "normal", anything under 10% as long as its on the low end. That was not the answer i was looking for.... but they wouldnt/couldnt adjust it.
You could get one of those hand held numbers, like Geraldo used during the galveston hurricane....
Andrew
I was just throwing it out there. But I use a GPS to calibrate my speedometer on the fly, and it's dead on. :-)
Just joshing, Sam. I just couldn't pass up the opportunity to get a laugh. ;)
I know that is GM's stand on speedometer calibration too.. We even see the certified versions such as ordered in a SEO package for law enforcement vehicles read 10-12 mph different than the standard stock clusters. They won't even let us do anything to the IPC's but remove and send back! Guess they are afraid we'll change the mileage somehow! We have just gotten to where we can program miles and hours on replacement IPC's now..providing they are set a 0 when they are shipped..
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my real concern over and above that I think a speedometer should be fairly precise and 10% in my opinion is ridiculous from a precision standpoint is the odometer. 7% on a 60,000 km lease is 4200km, that is significant, luckily I am no where near my limit, but more the principle.
Andrew
I know that is GM's stand on speedometer calibration too.. We even see the certified versions such as ordered in a SEO package for law enforcement vehicles read 10-12 mph different than the standard stock clusters. They won't even let us do anything to the IPC's but remove and send back! Guess they are afraid we'll change the mileage somehow! We have just gotten to where we can program miles and hours on replacement IPC's now..providing they are set a 0 when they are shipped..
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The vehicle method sounds like an AFV clip in the making to me. #-o :oops:
Sam will be starring in next season's StormChasers series driving the PIV...Pavement Intercept Vehicle.....
I think they had that a few times in this years episode with the broken frame/axle issues they kept having.
Hmmm, and how did you know my wife considers me a PERV? :-)
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:oops: