Question regarding Live Data (Pressure sensor). **solved**

[RoostWeather]

Hello,

I'm the proud owner of a new Meteobridge PRO2, and it's a lot to get one's head around, particularly as my station set-up (Davis VP2) is not quite a "typical" setup.

Anyhow, I'm trying to read the surface barometric pressure from the Live Data feed, and there are apparently two sensors reporting it, reporting slightly different values for pressure (but identical for temperature and humidity).

- Screenshot: http://starlingsroost.ddns.net/weather/temp/sensors.png

Presumably one of them is the Meteobridge, but why is it appearing twice, and with two slightly different MSLPs?

Thank you very much!

[Mattk]

To begin how is the MBPro2 connected to the VP2? And maybe you could explain what not quite a "typical" setup means?

Obviously with several pressure, temp and humidity sources there can be variations depending on the station setup, sensor mapping etc have you implemented any calibration offsets, factors etc

On the System>Administration>System window how does he Power data: (Box Climate values) compare to Live Data System #9 corresponding values?

thb0!9press is system pressure and in your example corresponds to (1031.2hPa)
thb0!9seapress is system sea level pressure 1038.4hPa (all things being equal)

thb0!0press which is simply sensor pressure Indoor (Pressure)
and thb0!0seapress Indoor pressure 1038.9hPa (normalized, computed to sea level)

Under [Min/max Data] tab you should notice Pressure, Sealevel pressure, System pressure and System Sealevel pressure, hover mouse over sensor, note the physical sensor & mapping ID and correlate the [Now] value against the [Live Data] tab to match values

[RoostWeather]

To begin how is the MBPro2 connected to the VP2? And maybe you could explain what not quite a "typical" setup means?

MBPro2 is connected by direct RF readout from the sensors. So I have a VP2 ISS (Temp/hum and rain only on Transmitter 0), and a second rain gauge/anemo connected to a Sensor Transmitter (on Transmitter 1). Under the options for sensor configuration there is ISS, wind station, rain station, etc, but no option for "wind and rain station", so I've ended up selecting ISS twice. It does appear to work but I'm not 100% confident. That is what I meant by "not-typical", as it doesn't appear as an option in MB.

Obviously with several pressure, temp and humidity sources there can be variations depending on the station setup, sensor mapping etc have you implemented any calibration offsets, factors etc

I have a Weatherlink console 6313 (the new, touchscreen version) to view the data, it also has barometric pressure but as far as I know it doesn't transmit data anywhere (apart from upload to weatherlink.com). So the only pressure available to MBPro2 is from the sensor within it. I have not entered any calibrations, and I have some sensors mapped (eg physical wind/rain sensor from ISS#2 to logical wind/rain sensor) but my question here is about physical sensors which the MBPro2 are reporting.

thb0!9press is system pressure and in your example corresponds to (1031.2hPa)
thb0!9seapress is system sea level pressure 1038.4hPa (all things being equal)

thb0!0press which is simply sensor pressure Indoor (Pressure)
and thb0!0seapress Indoor pressure 1038.9hPa (normalized, computed to sea level)

Understood - but I still don't understand why there are "two sensors" reporting pressure, even less so why it appears to be the same sensor reporting a true pressure, that is then being adjusted to sea level using slightly different corrections for each sensor given everything else is identical. What is the difference between system pressure and sensor pressure? As far as I can tell, from everything described, there is only one pressure sensor available to this system.

Thanks very much for your help

[admin]

PRO2 has a very precise BMP390 pressure sensor from BOSCH. As you can see, station pressure is reported identical, the variance is just with computed sea level pressure. Reason is that there are different formulas how to compute sea level pressure.

The one used to mesh with Vantage RF data (thb0) is close to how Davis computes sea level pressure. By this it is closer to what is shown on the Davis console, while there always is a slight difference.

For system data (thb9) a more general sea level formula is used, therefore you see minimal difference.

I would recommend to go with thb0, which is also used for reporting to weather networks, unless you map differently on "Sensor - Mapping" tab.

[RoostWeather]

Fantastic, thanks very much!

[Mattk]

The minor difference in sealevel pressure between [System #9] & [0 indoor] also fluctuates/cycles as the [Live data] tab updates independently, Signal wise. If one sets the station altitude to 0 (zero) and as using RF the indoor data inherits System #9 values and straight up Temp/Hum/Seapress/Sensor press are identical but as each Sensor updates at varying/different/lag intervals there is some minor differences pop up with [0 indoor] values except (sensor press) which tends to be fairly stable. At 0 altitude Temp at times differed by +/- 0.1°C, Hum by 1% and sealevel pressure by 0.1hPa or so.

Crank up the altitude a little and one starts to see sealevel pressure fluctuating by 0.4/0.5hPa, then both be equal then would wander off again. As mentioned sensor pressure (in brackets) is quite stable but [0 indoor] wanderings appear to be a bit of Signal time lag (as was observed), maybe some rounding influence etc