First post!
Welcome!
I have had the WS-2000 for a few months now and have returned back to the issue of properly calibrating atmospheric pressure. Galfert's posting about a new web based tool to help calibrate pressure prompted me to take a second look at my settings. A hat tip to galfert!
As a PWS newbee I confess to being entirely confused about Absolute pressure, relative pressure, station pressure, altimeter pressure,etc.
Well thank you! Glad you found the information I posted helpful. I think you understood it pretty well and you almost got it.
Absolute Pressure is the same as Station Pressure. This is the pressure indicated by a calibrated barometer (but not yet corrected to Sea Level). This is the raw pressure at your elevation.
Relative Pressure is your corrected pressure to Sea Level. That could be Sea Level pressure or for some people that choose to do so it means Altimeter. This is a personal choice if you make Relative = to Sea Level or = to Altimeter. This is an argument that I don't want to hash up here yet again. Just pick one...or ask elsewhere which one to make Relative pressure be equal to Sea Level or equal to Altimeter. If you don't know just use what number the airport says and take that to be Relative. Sea Level Pressure and Altimeter differ slighting in formula used to correct for elevation and they also serve different purposes for some people. At lower altitudes Sea Level and Altimeter are almost the same...at higher elevations they start to drift from one another and also when the temperature swings too hot or too cold you'll also see differences. This is because Altimeter's formula uses a fixed standard temperature of 59F and Sea Level pressure uses an average of the previous 12 hours (that's the basic difference...without going into details why one versus the other).
In re-reading the manual and reading ( a lot) of posts here, I just wanted to make sure I am on the right track.The manual suggests adjusting Relative pressure to the closest airport weather station. That is where I got into trouble.
First of all, my pressure settings became entirely wonky as I was trying to adjust Absolute pressure and Relative pressure at the same time. I got the impression of chasing one's own tail.
Yep, that is exactly what it feels like (chasing one's own tail) if you don't follow the right steps. It is unfortunate but with Ambient it is a bit counter intuitive to calibrate pressure. But once you see the whole picture it just clicks in your head and it is like a eureka moment of clarity. Hang in there. Using the nearest airport is still good practice even if it isn't close. You can look at isobar maps and calibrate at times when you fall on the same isobar line. I like to use Windy.com for this but you can use other sources for looking at isobars. I should probably create a new tutorial on how this is done and how that works. I'll try and do that at some point.
I wanted to get back to the default settings. Can I assume that measured pressure from the external indoor sensor (WH32B) is Absolute pressure and that the reading on the WH32B sensor should initially be the default Absolute pressure on the calibration screen of the WS-2000? At least as a starting point?
There is no need to get back to a starting point. I suppose you could factory reset but it really is not necessary at all. Just see below for what to do. You are almost there.
The WH32B has an LCD display that will show you somewhat of an Absolute pressure. I say somewhat because you can't calibrate it. It was calibrated from factory but from what I've seen they do a poor job of calibrating these. I ignore the reading on the WH32B LCD display. Once you have your station calibrated you'll see that it is most likely off. So just ignore that display. But yes you are correct that it could be a starting point for the WS-2000 display. You set this as a starting point by setting Absolute to match it if you want. But it really is a waste of time I think. It is an extra step that will just get undone as you move on to the next step.
Since I reside in Canada, I use hPa as the government weather service up here uses kilopascals. The use of kilopascal however causes a slight problem as it is not as accurate as hPa. For example if my current reading on the display console is 1023.5 hPa , the closest Environment Canada weather station might report it as 102.3 kPa or maybe 102.4 kPa rather than 102.35 kPa You lose the last digit. Not sure if they round up or down.
Interesting I knew Canada used this but I didn't know that they dropped a digit. Doesn't matter if they just chop it off or round up. When you calibrate your station it will be something you do over a number of days and you fine tune it till you feel good about it. By the way this fine tuning is done by changing Absolute to affect a change then in Relative. Yeah ....too soon...forget that part for now.
If my understanding is correct, in order to calibrate pressure manually you have to convert measured pressure at current altitude (Absolute Pressure) to sea level pressure(Relative pressure). This the offset calculation that galfert kindly points out.i.e. 1013.25 hPa (sea level pressure)minus measured pressure (Absolute pressure)at current altitude = offset pressure
Since my altitude is 192 meters, the offset should be 22.76 hPa according to the web based calculator.
So if I have not gotten everything wrong so far you ADD 22.76 hPa to the measured air pressure (Absolute pressure) on the external sensor to get the corrected sea level Relative Pressure?
You are absolutely correct. See you got it. But here is the part that you don't have to worry about. You don't need to know what Absolute pressure is yet. You just need to make Relative Pressure be that much different than whatever Absolute is currently showing. You are not calibrated yet. This step is not to calibrate any pressure yet. This step is only used to tell the WS-2000 console at what elevation you are at. Since you can't give it 192 meters you are basically doing that indirectly by making Relative pressure be that much 22.76 hPa more than whatever it currently thinks is Absolute. With this step complete you now have your elevation set. Next step is to calibrate with airport.
The Environment Canada weather station is reporting right now 102.5 kPa and my newly calibrated WS-2000 reads 1022.5 (102.25 kPa)so I am off by .25 kPa which seems it is off quite a bit.
However galfert suggested adjusting absolute pressure to get the required offset. i would have thought you set absolute to measured and then adjust relative pressure to obtain the calculated offset. Confused? Relatively and Absolutely! Any help to clarify would be greatly appreciated.
Yes this last step is where you definitely are confused. But hopefully I made it more clear in my previous statement. In the previous step you dialed in a 22.75 hPa difference between Absolute and Relative. This is entered in by adjusting Relative. So when you adjust Relative all you are doing is entering in the difference between Absolute and Relative. You know this to be 22.75 so you never want to change that. So you never again touch Relative pressure in the console. But just because you can't touch Relative doesn't mean you can't affect a change in it by moving Absolute up or down by any given amount you need. What you are doing is adding or subtracting from whatever number Absolute is set while you actually are looking at Relative. In other words after you have the difference between Absolute and Relative you then look at what Relative is showing. Then you compare your Relative to the airport. Then you decide by how much you'd like to move Relative up or down to match the airport. You need to do some math and ask yourself how much you are off. That amount that you are off is what you add or subtract from Absolute. See by moving Absolute up or down by that amount you also move Relative up or down by the same amount....AND it automatically maintains the 22.75 difference between them.
So it is just two steps. 1) enter in elevation by putting in the elevation offset. 2) calibrate but do so by adjusting Absolute to indirectly affect the same change amount in Relative.
This is why you don't need a starting point with Absolute. Once you finish these two steps you then learn what the real Absolute pressure is at your elevation. Then you can if you want look at the WH32B and see how much they differ. That difference is just the factory doing a poor job at calibrating the WH32B. But it doesn't matter...because your WS-2000 will be correct for both Absolute and Relative.
Changing Relative: All this does is set a difference between Absolute and Relative. Never change this to actually calibrate Relative. This is how the station learns of how high your elevation is.
Changing Absolute: All this does is move Absolute and Relative up and down by the same amount. They stay hand in hand because the other adjustment was to set this difference. This is what you change to actually calibrate. You enter in a change to Absolute and it changes Relative by the same amount up or down that you entered.
* Very important. On the WS-2000 it is necessary to adjust Relative Offset (difference between Abs an Rel) and then you need to back out and go back to the main screen. Do not change both Relative and Absolute at the same time....or you'll be chasing your tail.....because you need to set the offset between them first and that doesn't get finalized till you back out to the main screen and then get back in to calibration menu.
