"'Tomasz Lewicki' via weewx-user" <[email protected]> writes:
> Please help me understand the workflow for pressure/barometer calculations > in Weewx. First, read this: https://github.com/weewx/weewx/wiki/Barometer,-pressure,-and-altimeter Given auxilliary data (temperature, humidity, elevation), one can convert between pressure/barometer and pressure/altimeter. weewx has code that when a driver reports some but not all of those, it can calculate the rest. Different consoles have different behavior. I will assume that a console should display barometer. Physically, consoles measure station pressure. > Here’s the situation. Let’s say my barometer reads 970 hPa. Setting aside > how the reduced pressure is calculated, I know that it underestimates the > pressure by 6 hPa. I’d like to inform Weewx of this without using the > weather station console—that is, without physically entering corrections > into the console. In other words, I want to do this in weewx.conf. There are assumptions lurking in your statements, and I'd like to draw them out. The correct approach is for the console to have: - an altitude setting - a station pressure calibration offset (well, it could be an offset at some pressure and a slope, or more complicated but I've never seen that in any instrument people use with weewx) and then for the console to calculate baromter. You haven't said what kind of station hardware you are using, and more importantly, what values it reports. You are saying you "don't want to" do this in the console, but you don't explain why. I think if you can adjust station pressure in the console, that's the best place. You say it underestimates barometer. You didn't explain how well you have determined height -- which is quite difficult, and it's roughly 0.12 hPa per meter. Your 6 hpa is likely some combination of station pressure error and altitude error. That's a lot. I would be suspicioiukous of the hardware at anything over 3 hPa error. Because of the error being caused by station pressure reading error and altitude setting error, it's likely to change somewhat. You are going to have some second-order error from applying a barometer correction, but I suspect that's in the noise compared to your other error sources (like time variation in station pressure error). > I’ve made the following changes: > [[[Units]]] > [[[[Groups]]]] > group_pressure = hPa > > [StdCalibrate] > [[Corrections]] > pressure = pressure + 6.0 > > [StdWXCalculate] > [[Calculations]] > barometer = WHAT SHOULD BE HERE? > pressure = AND HERE? In order to decide what to do, you need to understand for each of barometer, pressure, altimeter if they are reported by the station or not calculated by weewx or not (and obviously, if not reported, must be calculated) Under [StdWXCalculate] [[Calculations]] There are configuration directives to prefer_hardware. My advice is: Tell us what station hardware you are using. (Really, read https://github.com/weewx/weewx/wiki/Help!-Posting-to-weewx-user and include what was asked for and relevant. The OS part is very likely not important, but model of station, and how you have configured it is very important.) Understand which values are reported (turn on debugging and watch LOOP packets) and which are calculated, in the default setup. Consider setting barometer/altimeter to calculated, and go with with your correction to pressure (which is "Station Pressure") -- You received this message because you are subscribed to the Google Groups "weewx-user" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/d/msgid/weewx-user/rmiy0fnt21i.fsf%40s1.lexort.com.
