On 31/12/2018 17:09, Dave Liquorice wrote:
> On Mon, 31 Dec 2018 15:43:35 -0000, NY wrote:
>
>> Some time I'll have to take the base station (*) of my weather station
>> outside when it's windy and see what variation in pressure it records,
>
> Not sure it will but the pressure changes on a window due gusts are
> enough to make the glas flex. When we had single glazing and plain
> glass windows about 4' x 5' the center of that pane would move about
> 1/2" in response to gusts to 50 60 mph with a mean speed of 40+ mph.
> The double glazing with internal glazing bars forming six "panes" per
> top and bottom sash-a-like window still move but not as much, only
> about 1/4".
>
That is an entirely different scenario from an altimeter.

And more akin to an airpseed meter.

The pressure arises from momentom change as the glass is (somewhat)
orthogonal to the dierction of air movement. The aim of an altimeter is
NOT to slow any air down, just measure its pressure. So typically there
will be something like a chamber with holes in it everywhere so ensure
that the interiuors is full of air that is staionary WRT to the
altimeter, and at the same perssuer as outside,


>> though I'm not sure what electronic averaging there is between pressure
>> sensor and digital display. Indoors it's shielded by the house walls so
>> gusting isn't an issue.
>
> Wouldn't be so sure, with a gale or more blowing outside the pressure
> inside in reduced by a few millibars. Venturi effect I guess.
> Sometimes the wind just stops, goes from 40 - 50 mph sustained to <
> 10 mph in minutes, there is a noticeable step up in the internal
> pressure as recorded by the weather stations pressure sensor.
>

You can get that with open chimneys.


>> I wonder if I could see a measurable difference between the weather
>> station on the ground floor and in the attic.
>
> Ought to be able to. floor level ground floor to apex of roof above
> first floor won't be far short of 27' or 1 millibar.
>
Mmm


--
"When one man dies it's a tragedy. When thousands die it's statistics."

Josef Stalin

--- SoupGate-Win32 v1.05