Thanks for your reply.
The station is a weathersleuth professional, apologies I should have been
clearer. When I bought it I figured because of weewx I didn't need, or
want, an indoor screen.
https://www.aercusinstruments.com/aercus-instruments-weathersleuth-professional-ip-weather-station-with-direct-real-time-internet-monitoring/
Setting the station:
Absolute pressure offset = 0
Relative pressure offset = 0
The LCD screen in the barometer transmitter is showing the same value as
both absolute & relative pressure on the live data webpage.
If I stop weewx and listen for the data on the relevant tcp/ip port this is
what the station sends:
sudo nc -l 7890
GET
/weatherstation/updateweatherstation.php?ID=***&PASSWORD=***&tempf=53.6&humidity=76&dewptf=46.2&windchillf=53.6&winddir=31&windspeedmph=0.00&windgustmph=0.00&rainin=0.00&dailyrainin=0.00&weeklyrainin=0.00&monthlyrainin=0.00&yearlyrainin=29.46&solarradiation=110.48&UV=0&indoortempf=67.3&indoorhumidity=61
*&baromin=30.59*&dateutc=now&softwaretype=WH2600%20V2.2.8&action=updateraw&realtime=1&rtfreq=5
HTTP/1.0
The *baromin* value is the relative pressure. It doesn't send any other
pressure values.
If I offset in hardware it works and weewx reports barometer correctly
compared to local reliable sources but it doesn't (always!) survive a power
outage. Whats worse is the relative offset doesn't even stay defaulted to 0
- give it a few minutes and it does its own thing, literally a random minus
value based on no other setting I can find, unless I manually change the
offset value again but it only stays until it loses power.
My thoughts were to map *baromin *(relative pressure) from the station to
*pressure
*in weewx, leave the station relative pressure offset at zero and let weewx
calculate barometer as you suggest, of course double checking the altitude
value in weewx.conf is correct. Now I know it won't work after a power cut,
and I suspect even if I manually set zero offset and kill the power it will
initially return with zero and then change to a random value.
Station firmware is up to date - v2.2.8 is the last available.
However I'm starting to think I could get the pressure reading from
elsewhere. I'm running an Arduino in the greenhouse which is providing some
extra sensor data picked up by weewx using the Weewx MQTT Subscribe
extension.
Adding a barometric sensor to the Arduino should be pretty easy, mapping
its output to *pressure *in weewx.
Either that or read the station live data webpage into weewx but it seems a
lot of hassle compared to a buying a relatively cheap sensor. The one I've
just looked at claims an accuracy of 0.01mbar.
Maybe that's the solution - map an incoming MQTT topic
"greenhouse/absolutepressure" to pressure in weewx.
[[[greenhouse/absolutepressure]]] #mqtt topic sent from Arduino
name = pressure #weewx database table
.. and under
[[Calculations]]
Change *prefer_hardware* in the following entries to:
pressure = hardware
altimeter = software
barometer = software
Which I think would ignore the station relative pressure (barometer) and
since its not sending absolute pressure anyway I need not worry about a
conflict between the station and what the Arduino would be sending.
Also apologies again, I should have mentioned in my original post:
Weewx v5.1.0 (installed via pip/venv)
Raspberry Pi 4
Raspian (Debian) v12 Bookworm (arm64)
Aercus Instruments Weathersleuth Professional station.
On Friday 25 October 2024 at 12:03:49 UTC+1 [email protected] wrote:
--Hmm..if Absolute pressure and relative pressure = 0 (zero) your barometer
was not set up correctly and not calibrated correctly. II absolute pressure
= 0, you would be living in a vacuum! Or are you referring to both offsets
= 0?
Your station is the weathersleuth IP? If so, you have an outside array, a
Wi-Fi gateway and a separate LCD indoor sensor with a barometer sensor:
Thermo-hygrometer-barometer transmitter (temperature/humidity/pressure).
If your barometer is working, it should be reading the current atmospheric
pressure at your elevation (the elevation of your barometer). In your
calibration screen, you should see an absolute pressure offset and a
relative pressure offset. These fields are used to adjust your absolute
pressure and relative pressure, respectively.
It is best to start over from scratch. Set both offsets back to zero in the
calibration screen. Verify that the pressure showing on the LCD screen of
the external Thermo-hygrometer-barometer transmitter is equal to the
absolute pressure on your console. Maybe it's under the Live data tab?
You will have to calculate your relative pressure offset which depends on
your elevation.
Your weather station appears to be similar to an Ecowitt or Ambient weather
station therefore calibration procedures should be the same. Read the
barometer wiki to set your elevation and calibrate your barometer:
http://meshka.eu/Ecowitt/dokuwiki/doku.php?id=barometer#calibration_wi-fi_gateways
Your other question relates to WeeWX. You definitely do not want to pass on
your weather station's REL to WeeWX. Your weather station uses a single
fixed offset amount to do an estimate of sea level pressure. It can be a
reasonably close approximation but your readings will drift at times. You
would be far better off relying on WeeWX "barometer" pressure reading
because it uses an actual algorithm to calculate sea level pressure much
more accurately. To obtain the WeewX "barometer" reading you do not need to
configure anything. WeeWX will automatically calculate "barometer" from
your absolute pressure. BTW, the WeeWX "barometer" reading refers to SLP
(sea level pressure) that you might see on meteorological isobar
charts/surface analysis maps. If you follow the wiki's tutorials, your REL
(relative pressure) on your station's console should be an approximation of
the Altimeter setting.
On Tuesday, October 22, 2024 at 4:43:24 AM UTC-4 Ashley Hinton wrote:
Hi Michael
Thanks for your reply.
I did indeed read it which made me realise the issue is what WeeWx is
receiving (in relation to what its displaying on the webpage) & that it
needs to be calibrated somewhere.
I will first calibrate the hardware & then check what value from the
hardware is being displayed on the webpage. I'm pretty certain at the
moment Relative Pressure from hardware = Barometer on the webpage but will
double check so I know in future.
Thanks again,
On Monday 21 October 2024 at 04:56:31 UTC+1 [email protected] wrote:
Hello, as a first step, did you read the following:
https://weewx.com/docs/5.1/usersguide/troubleshooting/meteo/
After that, do you know the pressure mappings console <=> weewx? Then,
which of the values (pressure, altimeter, barometer) is displayed on the
webpage? If you know all these things, calibrate your hardware according to
the manual and choose your desired obs_type to be displayed on the webpage.
Ashley Hinton schrieb am Sonntag, 20. Oktober 2024 um 22:08:57 UTC+2:
Hello
I've noticed my Barometer reading is different from other local sources:
the airfield just up the road from me, the local weather report, my phone
weather app - you name it, my readings did not agree. WeeWx was reporting
too high.
I'm using an Aercus IP weather station and WeeWx is using the Interceptor
driver.
The weather station itself has its own calibration settings page, it has
two fields for calibrating pressure:
Absolute Pressure (was, and is, set to 0)
Relative Pressure (was set to 30.00hpa which I'm sure was arbitrary, now
set to 0)
If I change the Relative Pressure offset the Barometer value reported on
the resulting WeeWx-generated webpage changes, so I'm confident that
Relative Pressure is what's sent to WeeWx.
My question is what to do - calculate and set the calibration in hardware,
or in WeeWx? What is generally preferred or considered the best option?
Thanks!
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