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TOPIC: Messure average windspeed over a year

Messure average windspeed over a year 1 year 1 month ago #7

  • PiLo-Heinz
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Hi Paul,
yes - there will be a difference especially at low wind speeds.
This is typical for this kind of anemometer. They have a certain breakaway torque and therefore a minimum windspeed to start spinning.
Also with low wind speeds the friction will contribute most and will vary from sensor to sensor (and time).
So at low wind speeds you will experience the biggest uncertainty anyway.
But the big advantage of this kind of sensor is the great range where it is almost linear !
A wind generator generally will behave similar - below 3 m/s most of them won't deliver power...
I've prepared a diagram on that:


If you really want to be more precise at low wind speeds and therefore adapt the algorithm in the Python script - then use the linear regression formula : Windspeed [m/s] = (Impulse per second + 1.73) / 2.99
This bit of floating number calculation not really does a difference in effort ;)

Have fun !
PiLo-Heinz
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Nichts ist unmöglich :-)
Last Edit: by PiLo-Heinz.

Messure average windspeed over a year 1 year 4 weeks ago #8

  • 2paul
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Thanks again for visualization.

My problem is, that i need more or less precise to know, if the windspeed is more then 4 m/s average in the year. Otherwise it will not work effectively.
The windwheels, I am interessed in, have 2m in diameter in a height of 10-15m, really small wheels, compared to the "real" ones :)
And they start turning und produce energy at 2 m/s.
So i really need more precise in low values.

My max-values in the last days with the factor 0.34 were under 8 m/s.

My idea is, not to change the code, but setting the factor to 1, to just get the average impuls-counts per second, and then do the exact calculation after in excel or programming, that should work, right ??

And maybe one more question, the length of the cable to the windsensor dosnt matter, right ?? just for testing i connect it with a 20m cable, or do you think that will produces failures in the impulse measuring ?

Great support :)

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Messure average windspeed over a year 1 year 4 weeks ago #9

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Hi Paul,
yes - good approach ! Correcting the measurement data later in postprocessing should work.
But this will work even with the linear factor of 0,34. So you will not loose the convenience of observing live speed data.
The log data will be precise enough to reconstruct the raw data also with a fractional factor.
Regarding the cable length : in general the length will be limited. From my experience i'd guess that maximum should be around that 20m.
Although the sensor already is equipped with 2 resistors which reduce steep edges, which otherwise could cause unwanted reflections on the transmission line, there are other limiting effects. For instance just the plain cable resistance increases with length and leads to decreasing pulse voltage. At a certain level the counter input will not be triggered safely anymore, so it will start to miss pulses.
To a certain extend choosing a bigger copper cross section could help reducing resistance - but also the cable capacitance will increase with length and thereby smoothing down the pulses...
So roughly 20m will be absolute maximum :(
Just enough for the height of your wind wheel tower ... maybe an option to put the Raspi + PiLogger in the tower base ?
There are USB to Ethernet adapters even with mico-USB connector, suitable for Rasi Zero. By that you could connect it by long ethernet cable.
Just an idea.

Have a nice weekend !
PiLo-Heinz

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Messure average windspeed over a year 1 year 4 weeks ago #10

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You are right of course.
Have the actual windspeed and calculate later is the best option.

Perfect that it works with 20m cable, thanks again :)

And thanks for the tip with the PoE, thats a good option, I will see how i do it, but i think 20 m are fine for me.
Its just to get an idea, if its worth to think about windenergy in first case.
But when i have all installed, i can also messure the temperatur of my thermosolar watertank :) really a cool thing a pilogger.

I will give feedback und try to send some pics when all is ready :)

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Messure average windspeed over a year 1 year 3 weeks ago #11

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Hi again,

almost all working now correctly, just have one stupid problem:
In the first install i said "yes" to change my NTP-Server to the Router. But he dont have that function.

i changed the /etc/systemd/timesyncd.conf
[Time]
NTP=0.debian.pool.ntp.org
FallbackNTP=0.debian.pool.ntp.org 1.debian.pool.ntp.org 2.debian.pool.ntp.org 3.debian.pool.ntp.org
#RootDistanceMaxSec=5
#PollIntervalMinSec=32
#PollIntervalMaxSec=2048
Now my piWebMon dont start anymore, the sync works fine:
pi@wind:~ $ systemctl status systemd-timesyncd.service
● systemd-timesyncd.service - Network Time Synchronization
   Loaded: loaded (/lib/systemd/system/systemd-timesyncd.service; enabled; vendor preset: enabled)
  Drop-In: /usr/lib/systemd/system/systemd-timesyncd.service.d
           └─disable-with-time-daemon.conf
   Active: active (running) since Fri 2021-07-23 14:24:49 WEST; 5min ago
     Docs: man:systemd-timesyncd.service(8)
 Main PID: 227 (systemd-timesyn)
   Status: "Synchronized to time server for the first time 216.232.132.102:123 (0.debian.pool.ntp.org)."
    Tasks: 2 (limit: 877)
   CGroup: /system.slice/systemd-timesyncd.service
           └─227 /lib/systemd/systemd-timesyncd

Jul 23 14:24:48 wind systemd[1]: Starting Network Time Synchronization...
Jul 23 14:24:49 wind systemd[1]: Started Network Time Synchronization.
Jul 23 14:25:35 wind systemd-timesyncd[227]: Synchronized to time server for the first time 216.232.132.102:123 (0.debian.pool.ntp.org).

But the PiError.log says:
23.07.21 14:38:51 Warten auf NTP Sync
23.07.21 14:38:56 Warten auf NTP Sync
23.07.21 14:39:01 Warten auf NTP Sync
23.07.21 14:39:06 Warten auf NTP Sync
23.07.21 14:39:11 Warten auf NTP Sync
23.07.21 14:39:16 Warten auf NTP Sync
23.07.21 14:39:21 Warten auf NTP Sync
23.07.21 14:39:26 Warten auf NTP Sync
23.07.21 14:39:31 Warten auf NTP Sync
23.07.21 14:39:36 Warten auf NTP Sync
23.07.21 14:39:41 Warten auf NTP Sync
23.07.21 14:39:46 Warten auf NTP Sync
23.07.21 14:39:51 Warten auf NTP Sync

can you maybe tell me, where is the problem ?

Think, I found the error :)
i looked in the code:
 while datetime.now() <= LogZeit :                                       # Warten bis Zeit synchronisiert ist
                sleep(5)
                printD("Warte...")
                printE(getLogTime()+" Warten auf NTP Sync")

I just changed to the right timezone, before it was on central-Europe time, now i have one hour earlier, Canarian Island time, just wait that hour, and all should work, because of the written "Lastlog.txt" time... right ??

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Last Edit: by 2paul.

Messure average windspeed over a year 1 year 3 weeks ago #12

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Hi Paul,
did you change the time zone for instance ? The error log message is caused by a time inconsistency, where the last log entry appears to be in the future. The respective lines of code are:
while datetime.now() <= LogZeit :		# Warten bis Zeit synchronisiert ist
	sleep(5)
	printD("Warte...")
	printE(getLogTime()+" Warten auf NTP Sync")
printE(getLogTime()+" Start Log-Mode")
So may be the Raspi had run to fast in time and now there is a gap ?
You may want to edit the last line in 'LastLog.txt' to a better suited time - which will cause time inconsistency in the most recent log file.
So if you want to keep the data, just save it and then start a new period after successful start by twice pressing the button 'Split Log jetzt'
in 'Einstellungen 2'.

Greetings, PiLo-Heinz

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