Measuring wind speed
LSB
Posts: 175
I read with some interest (in the customer applications section) an article describing measuring wind speed using Devantech SRF04s. I'm thinking the same thing should be possible using PINGs. Only one aspect bothers me; how does that work? I understand that a measurement taken with TXer upwind and another measurement taken with TXer downwind would give results different by the difference in airspeed between (some Doppler like effect), but if both TXers measure the airspeed in both upwind and downwind directions how would there be any difference? Is this clear? One Transmitter would PING in the upwind direction and receive the echo in the downwind direction--the other would transmit downwind, but receive the echo upwind--wouldn't that cancel any net difference, or am I missing something here?
Mark
Mark
Comments
Having someone else read the original material might do two things: clarify if there is an error and get a lot more people working on a solution.
I would like to build a wind measuring device and this seems like a wonderful solution for measurement of typoon winds as there is less exposure to destructive forces.
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"If you want more fiber, eat the package.· Not enough?· Eat the manual."········
Not quite sure if they're the same, but it doesn't have moving parts.
Another method would be to use temperature sensors....I'm trying to set up an array and see if I can get them to give me wind direction (speed later).
The trick is that not all temp sensors have the same curve and precip would confuse things (as well as direct sunlight).
We are testing a precip device that is essentially a hot plate. It maintains a certain temperature at all times, and as precip falls on it, it cools down and requires more energy to bring it back up to temperature....this power has a direct relation to falling precip. At the same time, this unit will measure wind speed (as wind will cool the plate as well)....an ambient temperature sensor is used for a reference.
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Steve
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
I would imagine that you would have to use a humidity sensor to establish your "reference" conditions (for the precip detector), as well...or maybe I'm over-complicating it...
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Truly Understand the Fundamentals and the Path will be so much easier...
Post Edited (Tom Walker) : 10/24/2006 8:35:06 PM GMT
http://www.parallax.com/html_pages/resources/custapps/app_wind.asp
I think he modified the parts to include only one-way time of flight.· I don't think he's looking for the echo.
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no humidity sensor needed. They're just measuring the power to keep a plate at a certain temperature. When it's raining outside, the humidity is 100% so for rain I wouldn't expect they'd need to worry about it. But is Rh 100% when it's snowing? The liquid water content is smaller....hmmm!! haha
I'm sure there's some fancy formula to deal with evaporation into a saturated medium (ie. an amount of water will evaporate at half the rate when the humidity is half...dunno).
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Steve
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
You know, I remember reading an article about measuring wind speed by the cooling of a diode junction on a transistor exposed to the wind,,,,,
I believe it was in the Nuts&Volts magazine;
www.nutsvolts.com/toc_Pages/feb01toc.htm
www.nutsvolts.com/toc_Pages/aug04toc.htm
This link explains how it is done ;
www.elecdesign.com/Articles/Index.cfm?AD=1&ArticleID=3990
Bob
I’m sure there are easier ways, but ultrasonic also tells distance and has application in a rain gauge, snowfall depth… traffic count…
Mark
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Paul Baker
Propeller Applications Engineer
Parallax, Inc.
There's a neat way to measure Rh in a simple way...and that's to take a standard thermometer and put a bit of cloth on the end (can't remember what we call it - Muslin sleeve? - but it looks like cheesecloth). You put it on the end of the bulb and wet it. This is called a wetbulb. You then compare this reading to the 'dry bulb' (regular thermometer) and the closer they are, the higher the Rh. Of course there's a big fancy formula for this, that takes in to account height above Sea level and a few other things.
In the winter time, these sleeves will freeze, so instead you actually try to freeze a bulb of ice on the end of the thermometer. Put a bit of water on it and roll the thermometer around to get it uniform.
(sorry for hijacking this thread)
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Steve
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
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Paul Baker
Propeller Applications Engineer
Parallax, Inc.
Too much stuff..not enough brain...
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Truly Understand the Fundamentals and the Path will be so much easier...
I was only thinking of a simple, reliable way to know if it was too windy to fly R/C and maybe add some "bling" on the unused pins. For anything detailed/ complex/ requiring forecast I have TV!
As for hijacking the thread... it wasn't hijacked, the exchange of free ideas infers 'unstructured'. I'm still here, your still here--who knows maybe wind speed will come back around.
You might also use an encoder/pot coupled to the mast to determine direction.
:Tom, the 'sling psychrometer' was the little handled apparatus that the dry/wet bulbs sat in. You created airflow past the bulbs by whipping them around in the sling.
We also use "psychrometer motors' that just suck air past them at a certain volume. I think this is slightly more accurate than just having them sit in the open (there is a formula for psychrometric and non-psychrometric readings.
(we've got a really old psychrometer that has an old spring clock engine on the top that you wind up and it turns a light fan that draws air across the bulbs--brass and silver..nice!)
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Steve
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
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John R.
8 + 8 = 10
* If it's swiging, it's windy
* If it's wet, it's raining
* If it's shiny, the rain is freezing
* If it's white, it's snowing
Just us take this, attach an accellerometer (swinging), color sensor (white for snow, etc.) and you could probably get rain by measuring resistance with an R/C time circuit on the surface of the rock.
Or have a wireless web cam pointed at the rock :-)
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John R.
8 + 8 = 10
A few high output LEDs inside; maybe red flashes for max gust, green for average wind speed... Hmmm, I think white to make it glow proportionately to the intensity of the gust. On the roof it would keep all the neighbors informed!
Direction... how to indicate direction?
we were always told to make sure the dog wasn't sitting beside you as a few dogs were bonked in the process.
We've gotten rid of our Mercury thermometers and are now stuck with ways to measure· (manually) temperatures below -30degC -- I can't quite remember the number, but mercury freezes at a much lower temperature than alcohol therms.· Also, if your mercury thermometer freezes, it's no longer accurate after you thaw it.· ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
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Steve
"Inside each and every one of us is our one, true authentic swing. Something we was born with. Something that's ours and ours alone. Something that can't be learned... something that's got to be remembered."
Possibly a "flashing" code, 1 for North, 2 for NNE, 3 for NE...
Or a vertical array of LEDs, just the bottom for N, half the lights on for S, through the whole "stick" lit for NNW.
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John R.
8 + 8 = 10