Cumulus Windspeed value shows more than into WH1080 Display

[Bernd]

Hi,
sitting in front of my PC i still noticed that the graph for the windspeed into cumulus
and also the graph onto my website, made
by cumulus, shows a higher value for the windspeed than the WH1080 Basicstation Display
and also the windsensor itself is moving slower than it would be necesarry for the windspeeds
like cumulus shows.

To compare both results, the one of the WH1080 station and the one from cumulus, i made
two screenshots. The first screenshot shows the results of the easyweather software which comes
with the WH1080. The showen values seem to match with the values into the WH1080 display and
also what happened in the garden in reallity.
The windspeed is painted red. Into the time range from 11:00 to 13:00 it's nearly all the time less
than 2m/s. Some times it goes down to zero and some times i goes clearly under 1m/s.




No we take a look what Cumulus shows into the same time period.
Like we can see the windspeed into the same time range is mostly above 2m/s.
And 11:00 it shows around 3m/s, where the easyweather shows under 2m/s !
So what is going wrong there ?




Bernd

[nking]

Hi,

You are new to Cumulus and bound to have many questions so can I suggest you first go through all of the FAQ and Wiki info as you will often find the answer yourself i.e. Cumulus is showing a different wind speed compared to my console

[Bernd]

I can understand that my questions do disturb.
But i'm very astonished that you said that you get similar effects.
Until now i couldn't understand why this happen.

So i will go through the FAQ and the wiki to see if this behavior is a feature or a bug.

Bernd

[Bernd]

Back again.
If i have understood what Steve wrote into the wiki then cumulus does the
job to display the windspeed more accurate because of logging (depending to the logging value)
more often, for example every 1 min, instead of the 5min oft the wh1080 itself.
Even if both of them would set to 5min, they wouldn't log at the same time.
Therefor the graphs can look different. Ok, i have understand this.

But what happened when i compared the curves was not only a slightly different curve shape
(with approximately the same contents of the envelope.)
The cumulus curve shows high values that did not happened in reallity at this time.
I can say this because i observed it in this range. The station never measured such high values.

The slowly turns of the anemometer matched well to the wh1080 display and also to the curve
that the easyweather software showed. (with a part of windstill and some times of very low under 1m/s)
Into the same range cumulus shows (average) values that did not happened during this time,
certainly not in the average.
The display of the WH 1080 (that updated every 48 seconds) never showed for example 3m/s
into this time range.
But into the cumulus graph i can see this 3m/s value as average for this moment.

Hmm... thats very curios.

Bernd

[steve]

I'm amazed that you can watch the anemometer and know the wind speed to 1 m/s

You say (in the title) that Cumulus is showing higher wind speeds than the console, but you give no examples to back this up. If Cumulus is showing a higher average speed than the console, perhaps you could give some examples of the speed that Cumulus is showing and the corresponding speed shown by the console at the same time. Note that there can be up to 10 seconds between the console updating and Cumulus changing to show that value. But as the display only changes every 48 seconds, it's quite easy to write down a set of values over a few minutes. Be very careful that you really are comparing the same data - i.e. you don't have Cumulus calculating the average, and you are comparing the average speed in Cumulus with the 'wind' value on the console. And you definitely have the console and Cumulus set to the same units.

I've just tried this with mine - setting both the console and Cumulus to m/s, and watched it for several minutes, and Cumulus displayed exactly the same as the console.

[Bernd]

I'm amazed that you can watch the anemometer and know the wind speed to 1 m/s

You are not the first one who is astonished about this.
At least i can see if it's around 1m/s or more around 3m/s or if it's standing still.
About 3m/s it's hard to make an estimate.

If Cumulus is showing a higher average speed than the console, perhaps you could give some examples of the speed that Cumulus is showing and the corresponding speed shown by the console at the same time. onsole and Cumulus set to the same units.

The first time i noticed it was at the realtime plugin. It ever shows more than the console (if console means the display of the weather station).
I looked hundret of times to the value on the weather station and on the relatime plugin on the website, knowing that there still is a time offset between it.
But regardless how often i looked, the reatime showed ever higher windspeeds than the weather station
Both are showing into m/s.
Onto realtime plugin i saw also higher windspeeds than the weatherstation display ever showed in that observed range. That was making me suspicious.

So i will do like you said. I will look to the console and will write down all values i can see with time stamp every 48 seconds.
Than i will try to compare again.
Unfortunatley i have to wait for wind again.


Bernd

[Bernd]

i.e. you don't have Cumulus calculating the average, and you are comparing the average speed in Cumulus with the 'wind' value on the console. And you definitely have the console and Cumulus set to the same units.

sorry but my low english skill sometimes do make it hard for me to understand.
I should not set cumulus (into station menü) to calculate the 10 min-average, right ?
So first i have to unset this option that was set because of the nervous forecast.

Then i should look onto wheater station display and also on cumulus software start site to the value
of average wind speed and should write down both of them.

If both of them are showing the same values, than the curve could not going above the highest
value that i write down during observing.


Bernd

[steve]

The first time i noticed it was at the realtime plugin. It ever shows more than the console (if console means the display of the weather station).
I looked hundret of times to console and relatime plugin on the website, knowing that there still is a time offset between.
But regardless how often i looked, the reatime showed ever higher windspeeds than the console.

Do you mean the Flash gauge on the gauges.htm page? The needle on that gauge shows the 'gust' from the station (same as the 'latest' on the Cumulus display), so that will always be higher than the station average value. It will, however, always show the same as the 'gust' value on the station console. Just as the 'average' value on the Cumulus main display always shows the same as the 'wind' value on the console, and that's the value that gets plotted on the wind speed graph.

[steve]

I should not set cumulus (into station menü) to calculate the 10 min-average, right ?
So first i have to unset this option that was set because of the nervous forecast.

You can't compare the average speed calculated by Cumulus with the average speed on the station. I assumed you had Cumulus displaying the figure from the station, as you were trying to compare them!

When Cumulus calculates the average speed for Fine Offset stations, by default it uses the station's 'gust' values. This fits with how Cumulus does it for the Davis VP2 (for reasons that don't matter here) and many people found this gives a good average figure when compared with other sources. This will of course result in a higher average figure than the station average. If you want to get Cumulus to use the station's average speed to calculate the Cumulus average speed you need to set UseSpeedForAvgCalc=1 in the [Station] section in cumulus.ini (this is probably only documented in the forum somewhere).

[steve]

If you want to get Cumulus to use the station's average speed to calculate the Cumulus average speed you need to set UseSpeedForAvgCalc=1 in the [Station] section in cumulus.ini (this is probably only documented in the forum somewhere).

Actually, I'd forgotten that this isn't just an ini-file setting, it can be set on the 'station settings' screen in Cumulus.

[steve]

So is that all cleared up now, or have I just managed to confuse you even further?

[Bernd]

Hello Steve,

yes, a second before i wanted to put the cyanide tablet into my mouth i read your answer with the solution.
You saved my life !

i never thought that the value for the average windspeed could be generated by the values for the gust.
As i deactivated the "10-min average windspeed" option i have seen immediately that the graphs were
going back to "normal", good matching niveau.
Then i activated it again and followed your instruction to activate also the second option to generate he avg.
value from the windspeed value of the station and not from the gust value.

So that was exactly the reason why i ever saw higher values into my graphs then the values for the windspeed
that comes out on the display of the weatherstation. Now they are matching much more better.
I can not imagine to what reason someone would like to have it this way, but it doesn't matter.
For me as the "windenergy man" it's important to get that windspeed value into my graphs that was happend
at the anemometer before, at least the best matching.
May be the gust speed value could be interesting too, but seperate.

Thank you Steve, my cumulus now again is a step more perfect.

Bernd

[steve]

i never thought that the value for the average windspeed is generated by the values for the gust.

Well, yes, I suppose it might be confusing. But Cumulus works with a number of different weather stations, and that item that it uses for the calculation isn't always the 'gust'. On the Davis, it's simply the speed over each 3-second sample period, so it makes perfect sense to use it to calculate the average. I don't even know what that 'gust' value actually represents on a Fine Offset station; some kind of peak reading over the 48-second sample period.

Most people seemed to find that using that 'gust' value to calculate the average gave a good result for Fine Offset stations; from personal experience comparing my Fine Offset station and my Davis station, the Fine Offset average is far too low. So I left it as the default, but later I offered that option of calculating an average from the 48-second average values, so everyone can use the one they prefer.