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Wind vane solution !

Discussion specific to Fine Offset and similar rebadged weather stations
harrym1byt
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Wind vane solution !

Post by harrym1byt »

Steve was a little concerned about the random look of the wind direction plots, so I have just been having a look at the problem...

I have just been trying to observe the wind direct vane, to see if I can work out why it doesn't produce any sensible readings in Cumulus. This plots both an instantaineous (red) and an averaged reading (blue points) on the graph - neither seemed to offer any sensible direction.

Looking at the vane, it seems to spin round as fast as the anemometer. It is not well positioned, with the house on one side and trees on the other.

My thought is that it desperately needs some damping, but as an initial test I thought to try increasing the size of its 'tail', so its tail is much bigger than its nose.

I have simply added some doubled up duct tape so it sticks onto the tail at both sides of the tail and long enough so that it almost touches the anemometer cups as they rotate. This I did at 14:30, since when I now seem to be seeing an average wind direction which is a line rather than a scatter of blue points in the graph.

Check out the blue dots on my wind graph for today. Notice the change as from 14:30.

http://myweb.tiscali.co.uk/m1byt/weather/trends.htm

It is not a complete cure, but it does confirm the theory.
harrym1byt
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Re: Wind vane solution ! (I don't believe it)

Post by harrym1byt »

Something really weird is happening..... :o :o

I posted the above after watching the wind direction graph for the 4 hours following the modificication. At 14:30 when I did the mod, through until 17:30 and beyond, my blue dots were showing a fairly neat line wondering gently up and down the graph. At around 18:30 I shut Cumulus down and restarted it at around 19:00. My neat, blue, gently meandering line has been replaced in the graph during the above period, by random dots spread over the graph. I swear I have not touched a drop!
TNETWeather

Re: Wind vane solution !

Post by TNETWeather »

I think your main problem is:
It is not well positioned, with the house on one side and trees on the other.
I don't think there is really a "fix" for that.

You can make adjustments, but they will never remedy the actual root cause of the problem.
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steve
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Re: Wind vane solution !

Post by steve »

Interesting. Maybe there is a bug in Cumulus here.

The difference between the two displays you saw is that while Cumulus is running, it plots the graph values from the data that's it's reading from the station in real time - the data that the station updates every 45 seconds or so. When you shutdown and restart, Cumulus grabs any missing data from the data logger and puts it into the data file (currently Oct08log.txt). It then takes the last 24 hours worth of data and plots it. There are now less data points available to plot, depending on the logging interval of your station.

So you would expect the plots to look a bit different, but if you say you had a reasonable line before, you wouldn't expect it to suddenly turn into what you have now...
Steve
harrym1byt
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Re: Wind vane solution !

Post by harrym1byt »

Here (if I got it right) is the nice neat line graph, with below it what I saw after restarting Cumulus.
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harrym1byt
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Re: Wind vane solution !

Post by harrym1byt »

Wrong way round sorry!

The bottom one was the one I was enthusing about after adding the duct tape. The top graph is what I saw after reloading Cumulus. In the top one you can just see a rough line starting to reappear on the extreme right edge.

Would you like me to add Oct08.txt to a posting, so you can take look?
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steve
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Re: Wind vane solution !

Post by steve »

Yes please. There are a lot more points plotted on the restart graph; there should be fewer. I need to work out where they're coming from.

Also, it's a bit harder to see what's going on with the 3D graph. I've been thinking of changing that one so it doesn't go 3D, I don't think it's useful. Agreed?
Steve
harrym1byt
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Re: Wind vane solution !

Post by harrym1byt »

I swapped to the 3d graph because the blue dots were being hidden behind the red, you just could not see them.

After sending the above, mmy nice blue plot was starting to really show again, so I shut Culumus down and restarted it immediately. Nice blue plot was gone again.

I'll now try to attach the file.
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dane
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Re: Wind vane solution !

Post by dane »

As far as I can tell what is stored in the Oct08log.txt is the "current" direction, i.e. the red cross(es) - not the "average" direction, i.e. the blue dots.
Maybe it would make more sense to store the average direction?
That would produce a prettier picture for us having a Fine Offset station.
And after all: when Cumulus is restarted, the directions coming from the oct08log.txt are named "average", i.e. blue dots - which in fact there were not.
Ib
Ib
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steve
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Re: Wind vane solution !

Post by steve »

Thanks, Harry, I see what the problem is. The wind bearing value that I store in the data file is the actual value from the station, not the calculated average. For stations like the VP2 where the individual values don't stray around too much, this is OK as they are always close to the average anyway. For your slightly wayward wind vane, you lose your nice calculated average line and get all the slightly random 'raw' values instead.

Now, I could change it so that I store the average value in the data log file instead of the 'current' value. Ideally, I'd be storing both anyway. But this doesn't help when using 'history' data as there is only the 'raw' value available anyway. Again, I could be calculating the average from the history data, but there are not really enough values to calculate an average from - see recent discussion elsewhere on the forum.

So, I think I'm not inclined to change the way it works just yet, until I see if I can work out a sensible way to calculate the average from the history data.

One thing does still puzzle me - why do you apparently have more data points after a restart? I can see that you're logging every minute, but the graphs are also plotted once a minute during normal running...
Steve
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steve
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Re: Wind vane solution !

Post by steve »

dane wrote:As far as I can tell what is stored in the Oct08log.txt is the "current" direction, i.e. the red cross(es) - not the "average" direction, i.e. the blue dots.
Maybe it would make more sense to store the average direction?
That would produce a prettier picture for us having a Fine Offset station.
And after all: when Cumulus is restarted, the directions coming from the oct08log.txt are named "average", i.e. blue dots - which in fact there were not.
Ib
You got there before I did! Although I was looking at something else simultaneously :)

I suppose I could just change to storing the average, I don't suppose anyone would object. But see my other reply for why it wouldn't always be the average.
Steve
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dane
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Re: Wind vane solution !

Post by dane »

I'd vote for a change to the calculated average in the oct08log.txt.
I agree that there's nothing you can do about the number off the unit, but most restarts of Cumulus probably take place after less than say 12 hours, so at least most of the picture after a restart will contain averages.
Ib
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steve
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Re: Wind vane solution !

Post by steve »

OK, you've convinced me. If it's going to save just one value, it's probably more useful to be the average.
Steve
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dane
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Re: Wind vane solution !

Post by dane »

Steve,
you are quick :o I see a new build is available, changing the wind direction to average.
Downloading....
Ib
harrym1byt
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Re: Wind vane solution !

Post by harrym1byt »

Where is the new version please ? :shock:
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