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.

I realise that my Vantage Pro is coming up for 12 years old this April 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 that I could replace it with.

Personally I've always thought that the anemometer has always under read, that's probably because for twenty years of my life I was used to watching the trace from a Munro anemograph on an RAF airfield where there few obstructions. My anemometer for the last 10 years has been 35 ft of the ground on the top of our chimney and we aren't really in open country. The 8th was one of the windiest days I've seen in this part of Devon and I think the gust of 45 kts was the highest gust (max mean speed for the day was 22.6 kts) I've ever seen it register. A hundred yards away in the corner of our meadow a very large tree (~30 ft tall) was blown right over. The roots looked very shallow and in recent years other trees that were giving it shelter had been felled. But if you used the Beaufort scale to estimate the mean wind speed that lunch time you would have said it was force 10. So is it possible that a 45 knot gust can uproot a tree?.

I look at the cups spinning in a 20 knot mean, as it was on Tuesday and I wonder just how much faster they would have to spin to record a full gale, let alone a 103 knots. I think it's some kind of mercury switch that does the counting, how many revolutions a second would those cups be spinning at to measure 34 knot mean? And that's why I would like to see that kind of raw 2.5 second data. I suppose that you could strap the whole thing to your roof rack on a calm day and drive around in your car to see what it recorded!

Bruce.