Cumulus Support

I am puzzled. I use a WH1080 station. It is on a 10ft pole above roof height and is clear of any major wind shadows or eddy effects. My Cumulus software Wind animation is set to 2, Compass points are set to 16. The Wind Direction vane rotates freely (too freely perhaps), and the Wind Direction reports at about 50 second intervals. However the Wind Direction, 90% of the time, indicates a bearing of an exact 5 Degrees. Occasionally it reports an intermediate bearing, but not very often. Why should this be? Is there any reason why the bearing is almost always on an exact compass point? The calculation of average bearing seems to be OK and it is rarely on an exact compass point. Could someone explain why my Wind Vane is reporting in this way?

What do you mean by "an exact 5 degrees" - an exact multiple of 5? Fine Offset stations are only capable of reporting a bearing corresponding to one of 16 compass positions. But they only have 8 reed switches, so for positions between the 8 'main' compass positions, they rely on two reed switches operating at the same time, and quite often this doesn't happen. So a typical Fine Offset station only reports one of 8 compass positions most of the time, i.e. a multiple of 45 degrees.

Is your wind vane level?

Mine currently isn't. For that reason, whenever wind speed is below Bft 1, it settles into a position that is determined by gravity rather than by the wind direction. Which in my case means that it 'flatlines' at 338 degrees.

What puzzles me is that, if Steve's assessment is correct, this would be impossible.

peterh wrote:What puzzles me is that, if Steve's assessment is correct, this would be impossible.

How so? I didn't say they never report 'intermediate' compass positions, just that typically they rarely do. Yours is clearly able to report NNW successfully.

Peter - if you look at your wind direction graph, you get an idea of the problem. You have many more red crosses on the 8 'main' compass positions than on the 8 'intermediate' ones.

I know.

But that doesn't explain why the direction flatlines at 338 degrees when wind is below 0,3 m/sec... You'd expect it to flatline at 315 degrees or 360 degrees, but not exactly in between... right?

You'd expect it to flatline at 315 degrees or 360 degrees, but not exactly in between

As Steve said ....
Your kit reports 45 deg resolution all the time and sometimes has a good go at 22.5 deg.

Your vane is settling in between some 45 deg position and both reed switchs are operated.
Thus 338.5 rounded down

Yes, I guess you probably would, given what we know about Fine Offset stations; but yours is clearly able to report NNW successfully in that circumstance. My guess would be that when it's not moving, it's able to operate the N and NW reed switches simultaneously. The fact is that what I said in my first post in this thread is correct, and is borne out by a wind direction graph from just about every Fine Offset station out there, including yours.

OK, that would explain it.

It doesn't really worry me that much - I am under the impression that I am more interested in a substantial direction change rather than if there is a slight error in averaging out the direction point.

And if I'm wrong, I don't want to know

Hi Peter,

Around 338 degrees may be one of the directions where two (of your) relays do operate together. However, IIRC that direction is one of the quite "high resistance value" directions, so maybe the A/D conveter is inaccurate, or there is some current leakage (moisture) between the electrical contacts.

However, you could try balancing the vane with duct tape on the vane or "nose" as appropriate. I also balanced my anemometer with small strips of adhesive PVC tape inside the cups.

Cheers, Alan.

PS: @Steve: Except mine.

AllyCat wrote:PS: @Steve: Except mine.

Ah, yes indeed. An excellent modification.

AllyCat wrote:Hi Peter,

Around 338 degrees may be one of the directions where two (of your) relays do operate together. However, IIRC that direction is one of the quite "high resistance value" directions, so maybe the A/D conveter is inaccurate, or there is some current leakage (moisture) between the electrical contacts.

Could be - when there is no wind, I can actually see the wind vane pointing (as accurately as a visual inspection can assert) in that direction.
I have applied insulation paste to the surfaces where the contacts are, so they're not overly prone to moisture problems.

However, you could try balancing the vane with duct tape on the vane or "nose" as appropriate.

That is actually a genuinely good idea! Thanks! I will definitely do that when I'm going to take it down for the first major revision (when the paint on my Stevenson screen has dried).

My query was due to my complete ignorance as to how the Wind Vane operates. (I haven't had to take one apart yet!). My vane reports on the 4 Cardinal and 4 half-Cardinal points of the compass: i.e. O, 45, 90, 135, 180 Deg., and so on. I now understand, from this Forum, that the Vane has only 8 reed switches and therefore will obviously report on those 8 positions most of the time. Thank you Steve, and everyone for your help and guidance. My knowledge is improving daily. Your Forum is a tremendous help.