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Near Real-Time Windspeed Tests. Part 1 - Fine Offset Anemometer Weatherproofing
#1

Firstly, I'd like to thank Werk for all the hard work he's obviously put into the Weatherduino project over the years. An amazing piece of work ! So many features!

OK, here goes. I wanted a way of cheaply measuring wind speed in near real-time to bring the dynamic nature of wind into the living room so to speak, and so, I'm posting (in several separate posts) the results of some tests I've made. Aspects of this multi part posting maybe be useful for some people...or maybe not Smile 


ADDITIONAL FINE OFFSET ANEMOMETER WEATHER PROOFING

As cheap as the Fine Offset Anemometer is, it does appear to work quite well, but it does suffer from offering very limited protection against water ingress into the vicinity of the bearing. Any water ingress will for sure shorten the bearing lifespan, especially since it's not stainless steel. Despite the anemometer's low price I wanted a quick cheap method of increasing its resistance to rain. A simple plastic canister cap can be modified to act as a rain shield. A 52mm diameter plastic can cap has 3 slots cut into it that align with the anemometer cup arms. A bead of 2mm thick silicone sealant is applied around the top outside circumference of the stationary bearing housing to act as the second of two rain baffles. The cap is placed onto the anemometer arms, with the slot gaps in the cap being filled in with small cut out sections of glued on cap plastic Silicone sealant fills in any remaining gaps. Another bead of silicone sealant 2mm thick is applied to the lower inside circumference of the cap to act as the first of the two rain baffles. Oh, and a little bit of extra weight (silicone sealant) is added near the appropriate cups to dynamically balance the arms/cups assembly, as its weight distribution is not even due to both the single 'offset from centre' magnet attached on the underneath of the assembly, and the additional cap. This is done by holding the anemometer on its side and adding/removing weight by trial and error such that in any position across 360 degrees that the cups are manually moved to the cups stay stationary, with no tendency to rotate to a preferred position. Spinning in high wind speeds, an unbalanced cup/arm assembly will cause a lot of mechanical stress in the bearing and its mount. The pictures attached document the changes. The modified anemometer still needs to be calibrated using the 'moving car in calm conditions' method, but initial observations show its cup rotation rate versus windspeed is largely unchanged.

Cap with slot cut into it:

   

Rain baffles:

   

Cap placed over bearing housing:

   

Modification complete:

   



Part 2 will document a small electrical modification to the same anemometer by replacing the single reed switch inside it with 4 Hall effect sensors to produce a 1 mph resolution at all windspeeds in a 0.33 second gate measuring period. Although not strictly necessary, the additional Hall sensors do improve the wind speed resolution over small measuring gate intervals at low wind speeds. In reality there's little point in measuring windspeeds at time intervals less than about 0.5 seconds due to the physical response function of typical cup anemometers to varying winds.



regards
Hibs1
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#2

I never have any issues with water ingress or rusty bearings, possibly due to being situated in a low humidity area with not too much rainfall.
As for issues with the cups going missing, now that's another story Smile
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#3

(29-04-2018, 02:00)uncle_bob Wrote:  I never have any issues with water ingress or rusty bearings, possibly due to being situated in a low humidity area with not too much rainfall.
As for issues with the cups going missing, now that's another story Smile

I have read stories of Fine Offset anemometers lasting months or many years, clearly dependant on the ambient weather conditions, and how the bearing is affected. I guess you fall into the latter time bracket? Out of curiosity, can you remember what the highest windspeed gust you measured was with the Weatherduino system? Here in the UK we've had a particularly wet spring and numerous heavy snowfalls (for us) over the last winter. Guess I'm just taking extra (maybe unnecessary) precautions on the weatherproofing front.

Yes, I saw your post of the broken anemometer cups recently. Quite disturbing really.

I'll also be posting some details of a diy anemometer build from scratch with which some of my near real time windspeed measurements were done.

regards
hibs1
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#4

(29-04-2018, 07:46)hibs1 Wrote:  can you remember what the highest windspeed gust you measured was with the Weatherduino system?

I can't remember but Cumulus tells me 97.9 kmh.
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