Author Topic: GW1000 Relative Pressure vs. Absolute Pressure  (Read 185 times)

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Offline tweatherman

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GW1000 Relative Pressure vs. Absolute Pressure
« on: October 21, 2020, 07:14:40 PM »
How can I convert relative to absolute pressure in inhg for displaying the correct absolute pressure reading  for my GW1000?

Thanks,
tweatherman

Offline galfert

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Re: GW1000 Relative Pressure vs. Absolute Pressure
« Reply #1 on: October 21, 2020, 07:56:26 PM »
The difference between Relative pressure and Absolute pressure is due to your elevation. If you know at what elevation you are at it is a simple matter of doing some math. But you can use the assistance of online web calculator to do the math for you. I understand you want the difference in inHg so that is just an extra conversion.

Use this site to figure out what the difference between Relative and Absolute should be at your elevation. Leave temperature alone at 15įC. Enter your elevation in meters!
https://keisan.casio.com/exec/system/1224579725

Use this to convert hPa to inHg:
https://www.convertunits.com/from/hpa/to/inhg

If you don't know your elevation then use this website and enter in your Latitude and Longitude (Degrees decimal):
https://www.freemaptools.com/elevation-finder.htm

Then enter in the calculated difference as the REL offset for the GW1000.
Then calibrate by adjusting the ABS to cause it to equally affect the Relative reading until the Relative reading matches the local METAR. Do not adjust the REL offset difference after you have entered that.

Or you can forget everything I said and only use this handy online tool that does everything (but you'll learn nothing):
https://caboose700.github.io/ws-barometer-offset-calculator/



« Last Edit: October 21, 2020, 08:02:18 PM by galfert »
Ecowitt GW1000 | Meteobridge (WeatherBridge)
WU: KFLWINTE111  |  PWSweather: KFLWINTE111
CWOP: FW3708  |  AWEKAS: 14814
Windy: pws-f075acbe
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Offline tweatherman

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Re: GW1000 Relative Pressure vs. Absolute Pressure
« Reply #2 on: October 21, 2020, 08:00:14 PM »
Thanks thatís a handful to figure out.

tweatherman

Offline Old Salt

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Re: GW1000 Relative Pressure vs. Absolute Pressure
« Reply #3 on: October 22, 2020, 07:42:51 AM »
Some folks make this more complicated than necessary.  It is relatively easy:

Use an online calculator to compute the difference between the absolute and relative values;
Enter the difference as a positive offset to the relative value, remember the relative value is 'sea level equivalent;'
Get the barometric pressure from the nearest 'official' weather station;
Compute 'official pressure' - relative pressure and enter this value as the absolute offset.

Monitor the official and relative pressures.  If there is a constant difference, adjust the absolute offset.  Do this on a regular basis, as your sensor may vary over time.  For the best results, do your initial calibration at the 'official' station after entering the relative offset. 

 

anything