Davis Ultrasonic Wind Sensor - What Units?

[themet...@gmail.com]

I have just replaced my Davis Vantage Pro2 wind sensor with an ultrasonic one. I live in the SW of Ireland looking into the Atlantic and the usual sensors only last a couple of years before seizing up with rust. In fact I notice they do not drain water properly from the Anemometer so collect water with salt in. A good mix for metal and electronics!

I have just got the Ultrasonic one up on top of my 10 metre mast. I have not done anything to the Console or Weather Envoy settings (I do not use Windows, only Linux). So Console is 'Large Cup' I do not have any other choice other than 'Small Cup'

In my weewx.config file under [StdConvert] section I have this setting:

target_unit = METRICWX

Looking at the output compared with my Campbell Scientific Ultrasonic Sensor at 6 metres, I suspect the Davis one is logging in m/s rather than knots,

I have put the two outputs into a spreadsheet and converted the Davis Output to Knots and I am pretty sure this is the case.

I would just like to be sure I am correct in my thinking.

[Graham Eddy]

given that you have set 'target_unit = METRICWX’, the raw values inside weewx are all in the format of the units defined for METRICWX. the unit for speed used in METRICWX is indeed ‘m/s’

whenever you display values, weewx converts from whatever the internal format is into the units you have requested. if you happen to be displaying in the default METRICWX units, it has no conversion to do, but you can request it in ‘knots’ instead (such as tag $windSpeed.knot) and let weewx sort out conversions

if you want knots as your default displayed unit (in tags, web pages, etc), change weewx.conf under [[[Units]]] [[[[Groups]]]] 'group_speed = knot’ (it is probably explicitly set to ‘m/s’ at present, or it is that by default if not present, you just need to override it)

(note that the configuration line always mentions the unit in singular - ‘knot’ not ‘knots’)

[themet...@gmail.com]

Great stuff! Thanks for the comprehensive reply.

Regards