Anemometer Update!

Tips, tricks and frequently asked questions
utakurt
Posts: 41
Joined: 01 Oct 2013, 22:00

Re: Anemometer Update!

Post by utakurt » 22 Nov 2015, 16:18

Simply said: yes - N indicates the north and the aneometer has to bee adjusted to this direction!

vassago
Posts: 2
Joined: 22 Nov 2015, 12:28

Re: Anemometer Update!

Post by vassago » 22 Nov 2015, 18:12

ok thx!!!

elraj
Posts: 50
Joined: 13 Nov 2015, 21:41

Re: Anemometer Update!

Post by elraj » 22 Nov 2015, 20:10

Stoffiss wrote:For those wondering about the sampling frequency of the wind gauge I've just been in contact with Netatmo. According to them the data from the wind gauge is sent every 5 minutes, and therefore a data point is created every 5 minutes (which we already knew). However, during these 5 minutes approximately 50 samples of wind speed, wind direction, wind gusts and direction at maximal wind speed are taken.
Wow, this is important information. This means that the wind gauge logs data every 6 seconds. I guess the highest value (over a 6 second period) during the 5 minute interval is being reported as 'gust'. In other words: a guest is the average wind over a 6 second period while most other amateur weather station (Davis included) defines a gust as the average wind during 2-3 second intervals (which is in accordance with the WMO standard)

So, when we are comparing the Netatmo gust with nearby Davis station, we are in fact comparing apples and oranges... Netatmo will always report lower gusts because of its longer logging intervals.

Please correct me if I'm wrong.

flappah
Posts: 19
Joined: 09 Jan 2015, 13:37

Re: Anemometer Update!

Post by flappah » 22 Nov 2015, 22:28

Well, if the anemometer is doing 50 samples over 5 minutes I'd say it means it takes 1 sample every 6 seconds. And that one sample is not an average of that 6 seconds but just one data point in those 6 seconds. If a Davis takes an average reading over a 2 to 3 second it means it takes more samples in this 2 to 3 second period. But you're right in the end, the readings of those two stations are very different indeed because of the different method they used.

elraj
Posts: 50
Joined: 13 Nov 2015, 21:41

Re: Anemometer Update!

Post by elraj » 22 Nov 2015, 22:46

flappah wrote:Well, if the anemometer is doing 50 samples over 5 minutes I'd say it means it takes 1 sample every 6 seconds. And that one sample is not an average of that 6 seconds but just one data point in those 6 seconds. If a Davis takes an average reading over a 2 to 3 second it means it takes more samples in this 2 to 3 second period. But you're right in the end, the readings of those two stations are very different indeed because of the different method they used.
Your are probably right. So while most other stations calculate gusts and average speed based on continous measurements, the Netatmo gauge readings are based on a data point every 6 seconds with no average calculation between the data points. In other words: 80% of the time it does not measure the wind speed at all.

I really hope they will re-evaluate. The gauge has an internal memory so technically I guess it should be possible to use the same method as Davis, Fine Offset etc.

flappah
Posts: 19
Joined: 09 Jan 2015, 13:37

Re: Anemometer Update!

Post by flappah » 22 Nov 2015, 23:46

Exactly!! So just reading a specific windgust is a matter of chance or just being lucky it seems to me.

It could be that the differences in sample rate can be the reason that the module seems to report a too low value. But then again, if it is a matter of statistics of "just getting the right windgust" and windgusts are being distributed random in time it shouldn't matter too much. Of course one can't compare values read at a specific moment but averaged over a larger time it should more or less display the same windspeeds.

I am curious how much internal memory the anemometer has. I mean, a typical float value takes up 4 bytes so a combined speed/direction sample takes up 8 bytes. Even an 8 Kbyte memory chip could hold 1024 samples. So why keep it at 50 samples? Upping the sample rate would at least make the meter more comparable to other anemometers.

elraj
Posts: 50
Joined: 13 Nov 2015, 21:41

Re: Anemometer Update!

Post by elraj » 23 Nov 2015, 19:19

flappah wrote:I am curious how much internal memory the anemometer has. I mean, a typical float value takes up 4 bytes so a combined speed/direction sample takes up 8 bytes. Even an 8 Kbyte memory chip could hold 1024 samples. So why keep it at 50 samples? Upping the sample rate would at least make the meter more comparable to other anemometers.
Yeah, it certainly has more storage capacity. And if it doesn't I guess they can make it transmit data to the main unit more often instead. My cheap Fine Offset station transmits data every 48 seconds. In that interval it makes 24 wind samples in addition to temperature, humidity and precipitation readings. Still, the two AA batteries last for more than two years!

WMO has defined a gust as the average wind during a 3 seconds interval. It would be a nice start if Netatmo can make their wind gauge calculate in the same way. Hopefully they will release a firmware upgrade at one point.

pogpol
Posts: 8
Joined: 27 Jul 2015, 09:31

Re: Anemometer Update!

Post by pogpol » 23 Nov 2015, 22:01

I have my Netatmo anemometer since Saturday. Today I decided to do an experiment. I compared the speed of air flow with Netatmo anemometer and handheld anemometer Skywatch Meteo. I used a hair dryer to produce airflow (cold, of course) on relatively constant speed.

The measurement was carrying out for about 20 minutes so that the anemometer could measure wind in at least one full five-minute cycle. Finally, there were 3 complete 5-minute measurements and their results were similar: 10 km/h average 5 minute speed and 14 km/h gust. On Skywatch anemometer: average speed (6 minute) 15,2 km/h and gust 16,6 km/h. So... it was quite similar!

But then I made another experiment: I approached a hair dryer's orifice as close to the Skywatch anemometer cups as I could to measure the maximum attainable speed - it was 59.6 km/h. Later, I did the same thing with Netatmo anemometer. I was doing that for 2 minutes and maximum recorded speed was 31 km/h.

Finally, I tried to measure the speed of airflow when I was driving a car with Netatmo wind gauge hooked to a camera tripod. I thought that the wind gauge registers the measurement despite the lack of connection to the base station, but unfortunately - no measurements were recorded.

xon
Posts: 21
Joined: 22 Oct 2015, 08:49

Re: Anemometer Update!

Post by xon » 23 Nov 2015, 22:10

WOW..what a great job you did..Netatmo should pay you!. Haha it must looked priceless..a car with 2 anemometer on top of it driving around in the street over and over again :-).

Stoffiss
Posts: 50
Joined: 06 Aug 2015, 12:12
Location: Sweden

Re: Anemometer Update!

Post by Stoffiss » 24 Nov 2015, 14:39

Recieved my rain gauge today and erm.. I think I might need to update my base station's firmware because I get quite unrealistic wind speeds INSIDE :lol: Don't know why the app didn't force the update upon pairing with the device?!
Image

EDIT: Now Netatmo has updated my base station (very good service! :))
Last edited by Stoffiss on 25 Nov 2015, 18:35, edited 2 times in total.
My devices
Netatmo Weather Station // Indoor module v119 // Outdoor module v43 // Add. indoor module v43 x2 // Rain gauge v8 // Wind gauge v14

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