Cumulus Support

Hello Guys and Gals
I am a complete newby with the Easy Weather WH1090, I am really struggling with the pressure readings getting them in the same ballpark even as the bbc forecast or private stations in the network. I have the pressure set at Hpa but dont know whether to set it on Rel or Abs, I know it may seem trivial to the experts but its baffling me.
What is the difference with Mb for instance.
I have the unit about 12 feet up a pole and as exposed as I can get it. I have my Latitude and Longitude , the height above sea level is troublesome but I still have to check its accuracy yet.
Thanks for any help you can give me.
All the best for the new year
Captain

You should use the relative setting. This is intended to be the pressure adjusted to sea-level, and hence comparisons can be made with other stations regardless of their altitude. You need to set your relative setting so that it matches a nearby official station, preferably at a time when the pressure is stable over a wide area, such as during a large 'high'. Just about now isn't too bad.

hPa and mb are equivalent. We should really use hPa now as that is the SI unit, but mb are still in widespread use (except in the US, of course, where they use inches of mercury).

captain wrote:...I have the unit about 12 feet up a pole and as exposed as I can get it. I have my Latitude and Longitude , the height above sea level is troublesome but I still have to check its accuracy yet...

You might want to check the following link to find the altitude (ASL) of you home/weather station:

http://www.earthtools.org/

You may will find that the pressure readings on the met office website are rounded down by nearly a whole millibar/hpa which is not very useful for calibrating your weather station which has a resolution of 0.1 mb normally.

You may also find correcting for the height above sea level, which is 1 mb for every 27 feet, still does not give an accurate reading due to the calibration of the weather station.

The best method I have found is to locate the nearest 2 or 3 SNYOP stations and use the sea level pressure given by the SYNOP reports on a day when there is high pressure (preferably more than 1025). This will give a reading to the nearest 0.1 mb and you will find nearby stations will give very similar readings, for example, last night at 20:50, Thorney Island was 1019.0 and Shoreham Airport was 1018.9 and mine was 1019.0 so I know it must be about right.

captain wrote: I have the unit about 12 feet up a pole and as exposed as I can get it.

We have been reliably informed that the pressure sensor is located in the Console, not the remote transmitter unit, so you ignore the height of the remote unit.
Mike.

Can I thank you all for your help, you have come up with expert advice and some excellent websites for calibrating and finding out my position and height above sea level, at last I am getting the same readings as others in my area, its been a steep learning curve but well worth it.
Part of the trouble was my eagerness to get it running and scatter approach to settings and collecting data, a slight adjustment to the console and it was away.

Thanks again
Captain

captain wrote:...its been a steep learning curve but well worth it.

Well, you are not done yet ... There is still much to learn, not necessarily about the station console itself but on how to organize and display your Web pages to eventually make them more personal.

captain wrote:Part of the trouble was my eagerness to get it running and scatter approach to settings and collecting data, a slight adjustment to the console and it was away.

One thing I have learned over the years is that reading the documentation before trying anything can, in most cases, help in getting installed/operational without too much aggravation ... except when the documentation is written in chinese english...

Repairman77 wrote:We have been reliably informed that the pressure sensor is located in the Console, not the remote transmitter unit, so you ignore the height of the remote unit.

Indeed Mike, even for the Vantage Pro2, the pressure sensor is inside the console, which console is usually inside our homes...

So, in the case of the Vantage Pro2, it is measuring the atmospheric pressure (column of air above the console). But since I have entered the elevation at which the console is located, the Vantage Pro2 is 'translating' the atmospheric pressure readings into barometric pressure (sea level) readings.