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
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Hi Freddie
I've already written it!
That was one of the main reasons to buy the VP back in 2004.
I don't tend to use the applications that I have developed to download, parse and display the VP data as much as I should do, and I've only written one or two blogs about it:
https://xmetman.wordpress.com/2015/1...it-rains-from/
I've been meaning to write an application to analyse temperature data and calculate the hours of frosts in a day, or the amount of time a temperature is above 25°C in a day, which would give me another way of visualising the almost 12 years of 1 minute data that I have.
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.
Bruce.