Maximum wind speed

[jeffgod]

My VP2 seems to be maxing out at a windspeed of 48.3 kph. I have several days and times per day where it has recorded 48.3 kph. I find it strange that it seems to be unable to record any higher windspeed. Does anyone have any ideas why this is happening? My station has been running since November 2009.

[lddaly]

How is your station sitting? Any obstacles, buildings, trees, etc.?

[ocala]

Just to see if it records higher take a leaf blower to it. If it max's out at 48.3 you may need  to have Davis service it.

[mackbig]

hmmm.. I just checked my almanac pages for Feb and March.  I have several days in each with a max gust of 42.6 and several with 46.3.    Seems odd to have those exact numbers coming up so much.  I could see 46.1 46.8 46.2....  I will look at actual data when I get home.

Andrew

[jeffgod]

There are no obstacles in the way. The anemometer is on the peak of my house, well away from any interference. I will think about the leaf blower idea.

[jeffgod]

How would I know how fast my leaf blower blows? I don't have the box or manual anymore.

[ocala]

Mine isn't a commercial unit but rather just a home use model with a 2 cycle engine. It "claims" it blows at 150mph which is pretty darn high. At the end of the outlet it may be close but I doubt it. If your anny is accessible give it a try. I would think it would at least be stronger then 48kph.

[Cienega32]

I question mine at times too. It never seemed to go over 46. Last week it hit 47 and finally 48.3 which is my station's high. A year or two ago I seriously questioned it and meant to take a leaf blower to it but never did.

Seeing another 48.3 makes it a "must do" or at least an inquiry to Davis tech.

Micro-climates are one thing but the same 48.3??? Too strong of a coincidence for me now.

FWIW - a VP2 station near by only showed a sustained max of 21MPH during sustained 35+MPH winds (the day of my 48.3).

[Cienega32]

I just realized the speeds here were KPH not MPH which makes it even stranger with the 48.3MPH I have.

I just spoke with Davis Tech Support and he never heard of any wind gauges having a limiting problem like this.

His explanation  is that the speed is a result of actually counting revolutions and any limiting would be a result of obstructions or siting problems. He really couldn't explain why the site a mile from me was "stuck" at the 21 MPH max yet shows a history of higher winds with anything other than obstruction or siting.

IMHO - I find it hard to explain away his solid 21.0MPH top speed during 4 or 5 hours of sustained 35+MPH winds with gusts all around us of 50+.

I stand corrected - that other station usually runs a max of 21MPH. On the day of our high winds, he went up to 22MPH. I just shot him an email about that and will post any info/insight he passes on to me.

[mackbig]

I found values above the two I quoted earlier... those were just repetitive numbers that jumped out.  My record gust is in fact 68.5km/h... but get this.  I hit that exact value twice.  Dec 9 and jan 28.  What are the chances again???  Very odd.  Only had the vp2 since October, so hopefully all those dupe wind records are just crazy coincidences.

Andrew

[jeffgod]

Today my maximum windspeed is again 48.3 kph. Same as March 13, March 28, March 29, March 30. These are recorded as high gusts. I don't know if it makes a difference between high wind and high gusts. These do seem to high rates of coincidence.

[dalecoy]

If it's convenient, I suggest that you re-seat the wind cup assembly.  Loosen the setscrew, slide the assembly out on the shaft and then back in as far as it will go, and tighten the setscrew.  See if that makes a difference.

[wxtech]

I should know all these conversions but the data is in my notes.  I'll do some computations tomorrow.  Ole man gotta sleep sometime, can't do it tonight.  Anemometer cup rotation speed to mph/kph.  Frequency to wind speed. 
I know this; 60 Hz on the wind speed signal line = 135 mph.  So, tomorrow I'll hook a signal generator to the SIM and see what maximum speed the VP2 can handle.
The VP2 ISS Installation manual, page 24 states: "If the cable length is greater than 540' (165m), the maximum measurable wind speed may be less than 100 mph (161 kph)."

[jeffgod]

I look forward to your results, wxtech. FYI, the cable length is about 110' for the anemometer in my situation.

[MikeInTX]

I just realized the speeds here were KPH not MPH which makes it even stranger with the 48.3MPH I have.

I just spoke with Davis Tech Support and he never heard of any wind gauges having a limiting problem like this.

His explanation  is that the speed is a result of actually counting revolutions and any limiting would be a result of obstructions or siting problems. He really couldn't explain why the site a mile from me was "stuck" at the 21 MPH max yet shows a history of higher winds with anything other than obstruction or siting.

IMHO - I find it hard to explain away his solid 21.0MPH top speed during 4 or 5 hours of sustained 35+MPH winds with gusts all around us of 50+.

I stand corrected - that other station usually runs a max of 21MPH. On the day of our high winds, he went up to 22MPH. I just shot him an email about that and will post any info/insight he passes on to me.

While on the subject of MPH I have to wonder how you are seeing a .3 MPH?  My VP2 only shows MPH in whole numbers and never any tenths.  BTW with my leaf blower held about 3 feet lower than my cups I see a max of 56.0 MPH.

[Cienega32]

MikeInTX - most of the data for me shows 48 or 48.0 in WeatherLink and my NOAA reports. My 48.3 is what was reported by Weather Display. Good to know about the leaf blower. Then again, how to confirm the leaf blower?

Andrew - your high gust is still only 42.56MPH. If you ever catch a 77.n KPH gust, my eyebrows will jump off my face.

Dalecoy - I did the re-seating routine and seasonal clean-ups last year with no changes

I'm looking forward to the results as well. FWIW, I use the standard wire length (25 or 40' is it?) to the wireless ISS.

[mackbig]

pat,
I know my "high" is not huge.  But we really did not have any crazy winter storms (or any for that matter) this year and I only have data back to October.  Hopefully catch a bigger gust come first spring t-storm.

Dont know if its a fluke, but my OS caught a 112k gust last May.

On my jan 28 (vp2 68.5k gust), my os measured 58k that day

Andrew

Andrew - your high gust is still only 42.56MPH. If you ever catch a 77.n KPH gust, my eyebrows will jump off my face.

[wxtech]

Call this preliminary test results.  I'll change this post after I do more tests and I'm sure of the results.
Davis specs:
reed switch closes/opens once per revolution with 50% symmetry
1 revolution of the anemometer cups = 2.25 mph
__________my__actual__tests___________________________________
A Davis VP2 wired on my workbench with a signal generator producing squarewaves; voltage ranging from 1.8 to 2.8 volts
Wind cable, red is ground, black is wind speed signal.
1 Hz = 2 mph indicated on the console (1 x 2.25 = 2.25) this wind speed is accurate after rounding.
10 Hz = 23 mph indicated on the console  (10 x 2.25 = 22.5)  this wind speed is accurate.
100 Hz = 156 mph indicated on the console (100 x 2.25 = 225) the 156 should have been 225.
The 100 Hz is equivalent to the anemometer cups rotating at 100 revolutions per second or 6000 rpm.  This speed shows an error in the maximum reported speed at this high rate.
I will do another test at several frequencies to plot the actual wind speed indicated to compare with the theoretical speed.
More test results will be posted here.  

[George Richardson]

Al,
Perhaps you could try 67Hz. Specs say only good to 150mph.
FWIW
George

[dalecoy]

Dalecoy - I did the re-seating routine....

I was suggesting that to jeffgod.   Sorry I didn't make that clear.

[johnd]

1 revolution of the anemometer cups = 2.25 mph

Strictly speaking, this should read: 1 revolution/second of the anemometer cups = 2.25 mph

The gating period of the WMII anemometers was 2.25 secs and hence one revolution per 2.25secs was 1mph. So the speed circuit was essentially a pulse counter with this gating period. I don't know for sure, but I wouldn't be at all surprised if this same period wasn't also carried through to the VP design - the VP/VP2 anemometer being essentially identical to the WMII one. After all, a measurement of a wind gust (by most intenational definitions) needs to be made over a period of 2-3 secs and so counting the switch closures over this period would fit in quite neatly with this gust definition.

And I'd concur with the idea that there is a maximum wind speed that it's sensible to check against. Most folk outside of hurricane zones are unlikely to see >100mph as a gust speed and so for most users, linearity up to 100mph would be reassuring. But I don't know what pulse shape is needed for accurate test results at higher speeds. I'm guessing that the increased capacitance of longer lengths of cable starts to degrade the rise time of the closure pulse, which is presumably why long anemometer cables are incompatible with registering high wind speeds.

[lddaly]

Regarding the repetitive numbers for max speed... I see them all the time - 11.5mph max 28 days since 10/09, 19.6mph max 19 days since 10/09, 20.7mph max 13 days since 10/09, etc. The higher the speed, the less repetitive.

I have hit the same all time max wind speed of 35mph several times since 02/09 and have attributed this reading to the anemometer sitting of 15ft (thanks to home owner association restrictions ). Based on its surroundings, houses, trees, etc. I don't expect it to read anything much greater than that.

[MikeInTX]

Regarding the repetitive numbers for max speed... I see them all the time - 11.5mph max 28 days since 10/09, 19.6mph max 19 days since 10/09, 20.7mph max 13 days since 10/09, etc. The higher the speed, the less repetitive.

I have hit the same all time max wind speed of 35mph several times since 02/09 and have attributed this reading to the anemometer sitting of 15ft (thanks to home owner association restrictions ). Based on its surroundings, houses, trees, etc. I don't expect it to read anything much greater than that.

My anemometer is sitting at 27 ft. unobstructed north and south with trees in the neighborhood east & west.  My max has been 35 mph in WL and observed on the VP2 console as well.  I do feel like there is something wrong with the readings.  As I stated earlier with a 140 mph leaf blower at as close as I can get about 3 ft. below the cups my max was only 56 mph observed on the console.

[wxtech]

Final results.
Using a Tektronix Type 114 pulse generator (analog) set for 2.2 volts output @ 50 Ohms load, square wave.  The frequency is measured with a TiePie HS801 digital scope/counter and/or a Parallax USB oscilloscope.  Nothing has been calibrated recently.
frequency, rps  console indicated wind speed
10.00 Hz          23 mph
14.92 Hz          33 mph
20.00 Hz          44 mph
25.00 Hz          54 mph
30.30 Hz          64 mph
35.17 Hz          73 mph
40.00 Hz          80 mph
45.45 Hz          89 mph
50.00 Hz          97 mph
55.55 Hz         104 mph
62.5 Hz           115 mph
66.66 Hz          121 mph
71.4 Hz            125 mph
76.9 Hz             133 mph
83.33 Hz           145 mph
90.9 Hz             146 mph
100 Hz               154 mph
111 Hz                157 mph
111 Hz                 0 mph
113 Hz                 157 mph
125 Hz                  6 mph
125 Hz                  20 mph
131 Hz                  44 mph
157 mph was the highest wind speed that I saw on the console.  As the frequency increased, the wind speed started over at zero and increased with frequency.
Don't use this data for alignment and calibration of your system.  This is strictly a test to help understand how the wind speed function works.

[wxtech]

Regarding the repetitive numbers for max speed... I see them all the time - 11.5mph max 28 days since 10/09, 19.6mph max 19 days since 10/09, 20.7mph max 13 days since 10/09, etc. The higher the speed, the less repetitive.

I have hit the same all time max wind speed of 35mph several times since 02/09 and have attributed this reading to the anemometer sitting of 15ft (thanks to home owner association restrictions ). Based on its surroundings, houses, trees, etc. I don't expect it to read anything much greater than that.

My anemometer is sitting at 27 ft. unobstructed north and south with trees in the neighborhood east & west.  My max has been 35 mph in WL and observed on the VP2 console as well.  I do feel like there is something wrong with the readings.  As I stated earlier with a 140 mph leaf blower at as close as I can get about 3 ft. below the cups my max was only 56 mph observed on the console.

Your 56 mph indicated may be the effect that I noticed when the speed maxed and then started over at zero.