Topic: Explore Scientific WSX3001-CM3000 Calibration

[Cartman]

Hi - this is my first post so forgive my ignorance on probably what is a very simple and a previously well discussed issue...

I have recently taken delivery of an Explore Scientific WSX3001 PWS and am very pleased with it. I have in the past had low entry range weather stations but wanted something to hook up to the internet to record data etc and it does what it says on the tin nicely (not a top-notch PWS that I know a lot of members on here will have/built, but it does what I wanted it to do)

I have hooked it up to WeatherUnderground.com and all works well on that front...

I would really appreciate some help with the barometric pressure calibration/offset values for Relative and Absolute options. On previous units I have had, it had simply been a case of entering the height above sea level at the location of the unit in metres or feet. This is slightly more technical and want to make sure I am setting this correctly - I am interested in meteorology but it is purely a part-time irregular hobby.

In the setup, it is prompting me for the offset values which although I have read up about - am still left a little confused. I understand the difference between Relative and Absolute, but after using some calculators to try and learn the correct offset value - am still unsure.

So I thought it may be easier just to give some current values here with the hope of someone giving me the correct figure(s) hopefully

Both offset values on the PWS are defaulted to '0' at the time of writing this - the current pressure reading where I live is 1001hPa and my PWS console is showing a Relative 1020hpa and Absolute of 998hPa.

The location of the PWS is 30m above sea level so if anyone could help me out on this - I really would appreciate it.

Many thanks for taking the time to read.

All the best

[daveb1965]

Also would be interested as I am at 50m.

[galfert]

Cartman,
If your station is at 30m then your relative offset should be 3.6 hPa. This may or not be the number you actually enter in for the offset. What this 3.6 hPa means is that the difference between your Absolute and Relative should be 3.6 hPa. The reason I say it may or not be what you enter in for an offset is because your station may already have an offset that you would need to take into consideration. See follow up post for more details on this.

Of note is that your stations elevation is not ground level elevation. You should consider the height of the display console from the ground. Think about if it is on the first floor or 2nd floor of the building as that would make a considerable difference. So are you really at 30 m....or did you forget to add the console height? Some people assume that the barometer is at the height of the outdoor sensor array and that would be incorrect. There is no barometer in that unit...the barometer is inside of the display.

I used this online calculator:
https://keisan.casio.com/exec/system/1224579725

Keep 1013.25 and keep 15°C. All you do is enter in your elevation and then click Execute. Then subtract 1013.25 from the resulting Atmospheric pressure P. That difference is your Relative Offset for your elevation.

[galfert]

Also would be interested as I am at 50m.

6 hPa offset.

[galfert]

Both offset values on the PWS are defaulted to '0' at the time of writing this - the current pressure reading where I live is 1001hPa and my PWS console is showing a Relative 1020hpa and Absolute of 998hPa.

That is strange that with both offsets at zero that the Relative and Absolute would not be equal. The difference you have between 1020 hPa and 998 hPa corresponds to 184.25 m.

Perhaps zero doesn't mean zero and your model station is using that elevation as some sort of average or maybe it deduced that if it has some sort of auto-calibration (that I wouldn't trust). If so then what you really need is to get the difference between 184.25 m and the 30 m which you are at. That is 154.25 m change that is required to the zero offset...which would mean that you need to have a negative offset of 18.3 hPa. as that is what equals 154 m.

[galfert]

By the way, the station that you have is also known as a Bresser brand. I recently read that WeeWX was updated to be compatible with your station, in case you were interested in expanding its capabilities.

It most definitely is not a Fine Offset clone no matter how similar it looks and no matter if other Fine Offset reseller companies also carry this, as many Fine Offset resellers actually carry more than one OEM products.

[Cartman]

Many thanks Galfert

Apologies it has taken ages to reply - but all that info is great and explains things perfectly. So in short, because of the height above sea level the HPa offset is negative 3 (rounded to nearest whole number - I don't think I am able to enter decimal places on my particular unit)

And yes, the PWS is located at 30m above sea level - the outdoor sensor(s) are at 32m.

My console settings default to displaying '0' when I log back in and it reports the 'current offset values' to the side of the relevant data box (I hadn't noticed that previously) and it currently reports absolute @ '0' and relative @ '-19' so your calculations look spot on.

Many thanks again for your help with this as I will now disconnect it from WU and reset the values correctly 

All the best