xmetman Wrote in message:
On Wednesday, 10 February 2016 15:04:08 UTC, JohnD wrote:
"xmetman" wrote in message
...

I suppose the Vantage Pro just collects 1 minute mean speeds and graphs
those values in its own LCD display, and it's down to the display software
on the PC to take the average of 10 of those one-minute values to produce a
10 minute mean. A one minute mean of 67 mph would be significantly higher
than a 10 minute mean (~x1.2 or more higher).
====================

Is it a VP you have (aka VP1 nowadays) or a VP2? If so, it might explain the
apparent default to small cups - that's not the been the default for a long
time. (Not that it makes a huge difference, it's just a different
second-order LUT that's applied for correcting speed vs direction AIUI to
account for effects of the anemometer arm geometry.

But why would you suppose that it collects 1-min means rather than averaging
out the full set of 2.5 sec gust values that are the values actually
measured?

Hi John

I know in the electronics it must collect data and average it out somehow, but as a programmer as far as I can see, the minimum resolution of the raw data it stores is 1 minute and not 2.5 seconds. All the data logger is collecting for wind speed I imagine is the number of revolutions that the anemometer cups make in 2.5 secs, and it would be a good idea if these values were accessible (even if was just for the last 10 minutes) before they were thrown away.
snip

that's why I would like to see that kind of raw 2.5 second data
It is available, Bruce. Davis publish details of their serial
protocol, and there is software available (Cumulus for example)
that uses it. Now there's a programming challenge for
you!

--
Freddie
Pontesbury
Shropshire
102m AMSL
http://www.hosiene.co.uk/weather/
http://twitter.com/PontesburyWx for hourly reports


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xmetman Wrote in message:
On Thursday, 11 February 2016 10:31:53 UTC, Freddie wrote:
xmetman Wrote in message:
On Wednesday, 10 February 2016 15:04:08 UTC, JohnD wrote:
"xmetman" wrote in message
...

I suppose the Vantage Pro just collects 1 minute mean speeds and graphs
those values in its own LCD display, and it's down to the display software
on the PC to take the average of 10 of those one-minute values to produce a
10 minute mean. A one minute mean of 67 mph would be significantly higher
than a 10 minute mean (~x1.2 or more higher).
====================

Is it a VP you have (aka VP1 nowadays) or a VP2? If so, it might explain the
apparent default to small cups - that's not the been the default for a long
time. (Not that it makes a huge difference, it's just a different
second-order LUT that's applied for correcting speed vs direction AIUI to
account for effects of the anemometer arm geometry.

But why would you suppose that it collects 1-min means rather than averaging
out the full set of 2.5 sec gust values that are the values actually
measured?

Hi John

I know in the electronics it must collect data and average it out somehow, but as a programmer as far as I can see, the minimum resolution of the raw data it stores is 1 minute and not 2.5 seconds. All the data logger is collecting for wind speed I imagine is the number of revolutions that the anemometer cups make in 2.5 secs, and it would be a good idea if these values were accessible (even if was just for the last 10 minutes) before they were thrown away.
snip

that's why I would like to see that kind of raw 2.5 second data
It is available, Bruce. Davis publish details of their serial
protocol, and there is software available (Cumulus for example)
that uses it. Now there's a programming challenge for
you!

--
Freddie
Pontesbury
Shropshire
102m AMSL
http://www.hosiene.co.uk/weather/
http://twitter.com/PontesburyWx for hourly reports


----Android NewsGroup Reader----
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Hi Freddie

I've already written it!

As far as I know, even using the Davis API you can only access minute data, and most of the time this is fine, but as I said in my reply, sometimes it would be good to get at the 2.5 second data that the 1 minute wind speeds are derived from.
Well I've written software that talks to the VP directly via the
serial port, and it downloads something known as "loop" packets.
These contain the real-time data.
I know that Davis supply a DLL for accessing the VP. I think that
downloads the loop packets too.

--
Freddie
Pontesbury
Shropshire
102m AMSL
http://www.hosiene.co.uk/weather/
http://twitter.com/PontesburyWx for hourly reports


----Android NewsGroup Reader----
http://usenet.sinaapp.com/

"xmetman" wrote in message
...

All the data logger is collecting for wind speed I imagine is the number of
revolutions that the anemometer cups make in 2.5 secs, and it would be a
good idea if these values were accessible ....

As Freddie rightly says, these 2.5sec values are available in the real-time
or LOOP data from the logger (see the Serial Tech Ref for further details).
But you must poll and process them on some external device as they become
available otherwise they are indeed lost as discrete packets. The shortest
interval records that can be stored in the logger for later retrieval are
indeed 1-minute - maybe this is what you're thinking of? (Actually, IIRC
wind speeds are actually measured over a 2.25 sec gating period at the ISS
and then the latest available value transmitted at 2.5625 sec intervals on a
VP2 set to channel #1 (it's a progressively different interval on other
channels)).

I realise that my Vantage Pro is coming up for 12 years old this April

OK, so that is likely to be an original VP (VP1). So the transmission
interval (channel #1) is indeed 2.5 secs on these older stations.

but I would like to think that with technology such as the Raspberry Pi,
that either Davis or someone else would be able to put together a cheaper
weather station

The problem with the RPi is its power demand (say 2W continuous). Most users
want a wireless sensor transmitter that is not tied to an external power
supply so that there's much more flexibility on where the sensors can be
located in order to achieve optimum sensor exposure (and of course no need
to worry about running a vulnerable cable out to the sensors). This is just
not compatible with anything as power-hungry as an RPi, at least not without
a solar panel PSU potentially costing as much as the weather station. It's
why microcontrollers rather than microprocessors are usually used in the
sensor transmitter - these allow a continuous power budget of maybe 20-30mW,
which is compatible with a small/affordable solar panel PSU running 24/7/365
even at higher latitudes.

Personally I've always thought that the anemometer has always under read..

That's going to be related at least in part to height and exposure, although
if you still have the original anemometer then the bearings will also be
seriously worn by now. Examples of the 7911 and 6410 VP1/VP2 anemometers are
calibrated in different orientations in wind tunnels to 150mph. This is
necessary to generate the lookup tables that are used to correct the
measured wind speed for the smallish errors in raw speed caused by the wind
flow from different directions interacting with the anemometer arm.

John Dann
www.weatherstations.co.uk

"Freddie" wrote in message ...

John, what is the expected lifetime of VP2 anemometer bearings?

If I had to estimate, I'd suggest eg 5 years at an average inland/lowland
location. Coastal locations are typically going to be windier and have at
least some salt spray in the air. Actually the 6410 anemometer design was
revised some 2-3 years ago, in part with new lower-friction bearings (for
enhanced responsiveness at low wind speeds) and TBH there hasn't been enough
field experience with the new design to get a real idea of whether expected
longevity is any different. But I'd hope that at least 5 years was going to
be the benchmark again.

JGD

On 11/02/2016 16:20, JohnD wrote:
"Freddie" wrote in message ...

John, what is the expected lifetime of VP2 anemometer bearings?

If I had to estimate, I'd suggest eg 5 years at an average
inland/lowland location. Coastal locations are typically going to be
windier and have at least some salt spray in the air. Actually the 6410
anemometer design was revised some 2-3 years ago, in part with new
lower-friction bearings (for enhanced responsiveness at low wind speeds)
and TBH there hasn't been enough field experience with the new design to
get a real idea of whether expected longevity is any different. But I'd
hope that at least 5 years was going to be the benchmark again.

JGD
Just get a Dines Pressure Tube Anemograph! I'm sure the output could be
digitised by some clever script kiddy!

Ah well, maybe not - there would be a lot of kit to be incorporated.
Does anyone know if any are still in use?

On Thursday, 11 February 2016 03:26:26 UTC, Jim Kewley wrote:
In message ,
Graham Easterling writes


Ho hum, welcome to winter 2015/16.

We've been having this sort of thing since November.


--
Cheers

Jim

Well, not quite, the peak swell height reached 19m! at the wave hub
yesterday, with a significant wave height near 35'

You don't 'often' get that sort of thing anywhere.

Graham
Penzance

No not round the Isle of Man, there's not enough fetch on the sea for
the waves like that to build up.

We've certainly had similar wind speeds on several occasions though, not
to mention rainfall. In this SE/SW centric group it's never noticed,
reading this place you'd think the world revolves round SE London, Devon
and Cornwall. Hence my impatience with people calling this winter
boring.

--


Jim

I live in SE London Jim and I haven't to my knowledge moaned about winter so far and I can't think of anyone else who does; live in SE London that is.

On Thu, 11 Feb 2016 16:20:42 -0000, "JohnD"
wrote:

If I had to estimate, I'd suggest eg 5 years at an average inland/lowland
location.

Mine's been going for seventeen years!

--
Alan White
Mozilla Firefox and Forte Agent.
By Loch Long, twenty-eight miles NW of Glasgow, Scotland.
Webcam and weather:- http://windycroft.co.uk/weather

"Alan White" wrote in message
...

Mine's been going for seventeen years!

That's excellent and I didn't mean to imply otherwise - there are some
individual anemometers that just seem to go on forever, but others that
might start giving problems after eg 4-5 years. No obvious rhyme nor reason
just individual variation.

But I thought the question here was more about when the bearings might start
to wear sufficiently so as to start introducing a degree of error into the
reading and that's where the very approximate estimate of 5 years comes
from. Alan, I guess if you tried rotating the spindle carefully by hand then
you might be feeling some roughness in the action compared to a new one.

"JohnD" Wrote in message:
"xmetman" wrote in message
...

All the data logger is collecting for wind speed I imagine is the number of
revolutions
if you still have the original anemometer then the bearings will also be
seriously worn by now.
John, what is the expected lifetime of VP2 anemometer bearings? I
know it will depend on how windy the location is - but a ballpark
figure would be useful if available.

--
Freddie
Pontesbury
Shropshire
102m AMSL
http://www.hosiene.co.uk/weather/
http://twitter.com/PontesburyWx for hourly reports


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"JohnD" Wrote in message:
"Freddie" wrote in message ...

John, what is the expected lifetime of VP2 anemometer bearings?

If I had to estimate, I'd suggest eg 5 years at an average inland/lowland
location. Coastal locations are typically going to be windier and have at
least some salt spray in the air. Actually the 6410 anemometer design was
revised some 2-3 years ago, in part with new lower-friction bearings (for
enhanced responsiveness at low wind speeds) and TBH there hasn't been enough
field experience with the new design to get a real idea of whether expected
longevity is any different. But I'd hope that at least 5 years was going to
be the benchmark again.

JGD
Thanks John. I asked the question because my VP2 anemo is nearly 9
years old, and was wondering when I might need to get my wallet
out! No sign of any low bias in the readings as yet!

--
Freddie
Pontesbury
Shropshire
102m AMSL
http://www.hosiene.co.uk/weather/
http://twitter.com/PontesburyWx for hourly reports


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