If this longish reply looks like a "how-to"... it is. Thought it might be useful to new WS-2000 owners who are not familiar with the terms Absolute Pressure, Relative Pressure, Station Pressure and how to calibrate barometric pressure.
There are many, many posts about calibrating pressure(s) on the WS-2000 and I have blantantly borrowed (stolen?) some of the material from fellow forum member galfert. Thanks galfert! Definitely use the search function of this forum to further research this subject.
This how-to uses Sea Level Pressure (SLP) rather than Altimeter pressure. Altimeter pressure is whole different discussion.
It should answer your question about properly calibrating your relative pressure and by necessity, calibrating the absolute pressure. As mentioned in other posts, absolute pressure is rarely used and because you may have to indirectly calibrate the raw station pressure from the WH32B pressure sensor, the raw station pressure reading on the WH32B s generally ignored once you calibrate barometric pressure.
If the WH32B was 100% accurate then Absolute Pressure would be equal to measured station pressure. Chances are it is not and you have to "calibrate" Absolute Pressure.
Clear as mud? Read on.
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METHOD D “It’s all relative or is it?”
How to calibrate the Ambient Weather WS-2000 barometric pressure – a beginner’s guideUnfortunately, the WS-2000 does not have an easy way to calibrate barometric pressure. It would have been nice to just enter your elevation and sea level pressure(SLP) from an airport and then you’re done!
All new users are faced with agony of figuring out the quirky way of entering and calibrating the barometric pressure of your new WS-2000 personal weather station.
I hope the following will help the new user:
Although you can properly calibrate the barometric pressure on the WS-2000 using other (possibly faster) methods, to better understand the reasoning behind making all these barometric pressure adjustments especially for a brand new user, it would be best to start with the white, remote control looking WH32B device that came with your weather station. You bought it – you might as well use it!
In this method we are going to use the WH32B station pressure readings as a starting point to properly calibrate the barometric pressure for the Ambient Weather WS-2000 personal weather station.
If you understand the general concept of barometric pressure - the higher the elevation (above sea level), the lower the barometric pressure then it becomes apparent that at a specific altitude/elevation your station pressure displayed on the WH32B device should be lower than at sea level by a specific amount (elevation offset). Or looking at it another way, if you live at an elevation above sea level, the sea level pressure (SLP) should be higher than your station pressure on the WH32B display. Yes, there is a formula for that!
Why not just use your station pressure indicated on the WH32B device that you got with your Ambient WS-2000 weather station? You could, but how would you compare your weather station with other weather stations if they are all at different elevations/altitudes? Someone living at the ocean’s edge (sea level) or at a mountain top will have vastly different station pressure readings. To make equal comparisons, all station pressure readings should be converted to equivalent sea level readings. These adjustments/calibrations are done on the WS-2000 display console in settings mode (the gear icon).
* The WH32Bdevice transmits indoor temperature, indoor humidity and barometric pressure to the WS-2000 display console. Temperature and barometric pressure is reported only in Imperial units. For the sake of this illustration, barometric readings have been converted to metric.
The WH32B device reports inside temperature, inside humidity and barometric pressure (station pressure) at your elevation. For better accuracy, convert the inHg pressure readings on the WH32B to hPa. For calibration purposes, you can enter the WH32B station pressure reading as inHg and then change the units to hPa in the settings screen in the WS-2000 console. Or, alternatively use an online calculator to convert inHg to hPa.
Example
From the WH32B display let’s assume the current Station Presssure = 26.61 inHg and your elevation is 1000m. 26.61 inHg converts to about 901.13 hPa. Enter this number as the ABSOLUTE PRESSURE in the WS-2000 console.
NOTE: The WS-2000 console displays hPa to one decimal point. For calculation purposes you can round up (or down) or truncate the last decimal; i.e 1013.25 could be entered as 1013.3 or 1013.2. Whichever method you use – be consistent.
Use this online calculator
https://keisan.casio.com/exec/system/1224575267 to convert 901.13 pressure at 1000m altitude to the equivalent sea level pressure using a Conversion to sea-level pressure calculator .
The online calculator converts the station pressure (atmospheric pressure) at your elevation (1000m) to the equivalent sea level pressure. Assume 15C as the standard temperature in the calculator. Enter the elevation and station pressure (atmospheric pressure). The equivalent sea level pressure is calculated to be 1013.25. Enter this number as the RELATIVE PRESSURE in the WS-2000 display console.
What have we accomplished so far?
1. We have put in the WH32B station pressure reading (converted to hPa) as the ABSOLUTE PRESSURE reading in the WS-2000 console.
2. We used an online tool to calculate the equivalent sea level pressure based on our station pressure reading and entered the calculated equivalent sea level pressure as the RELATIVE PRESSURE on the WS-2000 display console.
But wait! We are not finished yet.
Last step. We may need to do some fine tuning as your WH32B station pressure readings will not likely be 100% accurate due to manufacturing tolerances. We will likely need to adjust the ABSOLUTE PRESSURE up or down in order to adjust the RELATIVE PRESSURE closer to a known calibrated source. This could be a government weather station or a weather station located at a airport close to you. If you are not close to an airport with METAR readings, you can use windy.com’s forecasted barometric pressure isobars to fine tune to within about 1.0 hPa.
Tuning Hints:
Think in terms of ABSOLUTE PRESSURE = calibrated WH32B station pressure (at your elevation) and RELATIVE PRESSURE = SLP (Sea Level Pressure).
In order to adjust RELATIVE PRESSURE you will need to adjust ABSOLUTE PRESSURE on the WS-2000 console. RELATIVE PRESSURE readings will move lock-in-step with changes to ABSOLUTE PRESSURE.
Make sure that you are displaying RELATIVE PRESSURE (REL) on the main screen on the console. There’s a button for that on the display console. To change the display between ABSOLUTE PRESSURE or RELATIVE PRESSURE press the 5th button from the left. You’ll likely want to display RELATIVE PRESSURE on your display.
Don’t try to fine tune when the barometric pressure is nose diving or skyrocketing. Wait for a stable pressure day. A big stable high pressure system encompassing both your weather station and a close METAR station would be ideal.
Do not expect absolute perfection. Readings between your weather station and the airport may drift at times. Close is acceptable!
Hope that helps!
