Tomasz Lewicki <stal...@poczta.onet.pl> writes: > I'm trying to sort out barometer and pressure values. I own HP1001 clone. > Internal T/H/P sensor was calibrated with my friends certified barometer > before. Currently it sensor shows absolute pressure value 936,7 hPa and it > almost perfectly (+/- 1 hPa) aligns with very accurate numerical forecast > for my location. Same meteogram show also relative pressure 1007 (+/- 1 > hPa) for my location. METAR for nearby (43 km) airport shows 1008 hPa. > > Relative pressure displayed by my HP1001 is about 20 hPa higher than > absolute - obviously too low value because I'm located about 550 m AMSL.
I have not fully dealt with this and I don't know your hardware, but I have thought about it a lot. But some advice: do not just twiddle without understanding a station that reports other than station pressure and doesn't let you enter elevation/altitude (distance above the nominal 0 level at sea level ish*) is designed wrong. The station might be near the ground and it might be in an upper floor. There is no way to know elevation from horizontal location. use the proper terms when discussing and thinking. https://github.com/weewx/weewx/wiki/Barometer,-pressure,-and-altimeter understand the data flow of your station. surely it is measuring station pressure, but often it will convert to one of the others and then that is all you can extract. understand that weewx can convert, but needs to have altitude understand that measuring altitude is quite difficult at the 1m level, and that 1 hPa is about 8.3 m. reading a value from a non-RTK GNSS (GPS, Galileo etc.) is just not that accurate. There is a calibration for the sensor, which is perhaps adequately modeled as an offset in station pressure. you then have to get altitude right, and calculations right by adjusting altitude it is sort of like adjusting the station pressure offset. This may be the best you can do, depending on what the unit reports and how it gets altitude. Overall, I suspect your unit has got a bad elevation value for where you are somehow, and you have made it display station pressure correctly. It seems to think you are ~160m lower than you are. I would look on forums to find out how your unit is supposed to work. Or get a BME280, calibrate that with your friend's instrument (they are pretty repeatable but have multi-hPa absolute calibration), and use that as station pressure instead, and have weewx do it is software. * the meaning of elevation remains unclear. Probably the height according to your country's national vertical datum is appropriate. If you are really in .pl, that's probably in EVRF2007, but even if it's not, they are almost all very close. -- 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 weewx-user+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/weewx-user/rmiv8cwf3nh.fsf%40s1.lexort.com.
