Welcome to the Cumulus Support forum.

Latest Cumulus MX release v3.0.0 build 3050 - 1 May 2019.
Legacy Cumulus 1 release v1.9.4 (build 1099) - 28 November 2014

See the Wiki for downloading either version.

Vantage Vue wind reading increments

Discussion specific to Davis weather stations
Post Reply
wildeman
Posts: 5
Joined: Wed 12 Jun 2013 10:04 am
Weather Station: Davis Vantage VPro2+
Operating System: Windows 7
Location: Jilliby, Central Coast, Australia

Vantage Vue wind reading increments

Post by wildeman » Thu 18 Jul 2013 6:41 pm

I have just installed a Vantage Vue (metric) and noticed that high wind and gusts increment at 1.6klms. So all off the values I have for wind are divisible by 1.6, is there somewhere I can change the wind register to reflect a more accurate wind reading? Instead of having 1.6 increment readings all of the time?

Touchtone
Posts: 93
Joined: Tue 09 Apr 2013 11:36 am
Weather Station: Davis VP2 Plus & FARS
Operating System: Windows 7 Home Premium x64 SP1
Location: Gin Gin, Qld, Australia

Re: Vantage Vue wind reading increments

Post by Touchtone » Thu 18 Jul 2013 10:21 pm

As far as I know Davis stations read wind speed in increments of 1 mph & do a conversion to kph which equates to 1.6 kmh. Software such as Cumulus do report readings in 0.1 kph as long as you don't have it set to round wind speeds, in which case it will read in 1 kph readings.
WeatherLink reports readings in 0.1 kph as well.
The station screen only shows whole figures, which is usually close enough for practical purposes.

prodata
Posts: 198
Joined: Sat 05 Feb 2011 7:13 pm
Weather Station: VP2
Operating System: Windows - all flavours
Location: Littleport, East Cambs, UK

Re: Vantage Vue wind reading increments

Post by prodata » Fri 19 Jul 2013 8:16 am

Touchtone wrote:As far as I know Davis stations read wind speed in increments of 1 mph & do a conversion to kph which equates to 1.6 kmh.
That's correct, on two counts in fact. The VP2 anemometer (at least up until the very latest redesign - there's no definitive information on this new type as yet, but I doubt that it's any different) cannot generate wind data to better than 1mph resolution, because 1mph corresponds to one contact closure seen in the gating period of, from memory, 2.25 secs. And you obviously can't see a fraction of a contact closure - it either happens or it doesn't - so wind speeds can only measure in whole mph units. The ISS (and eg the logger) only deals in mph wind units - any conversion to display units such as kph is done immediately prior to display. Hence only the direct equivalent of integer mph units can be converted to other units and hence, as Touchtone says, the staircase of 1.6kph values (which you can then truncate, should you wish to do so).

And similarly, the logger LOOP record, which Cumulus reads usually to acquire its data, only has a slot for integer values of wind speed in mph units. And so once again only integer values of mph are available to Cumulus for conversion to other units. So exact conversion to kph values automatically leads to the kph staircase again.

This sort of thing is almost inevitable with units conversion. Most stations only generate raw data in one primary set of units and to finite/limited resolution. So staircases often happen with conversion to other units.
John Dann
Prodata Weather Systems
Littleport, East Cambs, UK
http://www.weatherstations.co.uk

wildeman
Posts: 5
Joined: Wed 12 Jun 2013 10:04 am
Weather Station: Davis Vantage VPro2+
Operating System: Windows 7
Location: Jilliby, Central Coast, Australia

Re: Vantage Vue wind reading increments

Post by wildeman » Fri 19 Jul 2013 7:29 pm

Thx everyone for your comments, very helpful.

Post Reply