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View Full Version : Barometers: What things can go wrong with them?



gunnar I am
11-07-2002, 07:22 PM
Bought this barometer at a junk sale.Seems like a well made instrument.If I draw air through the back or puff into it the needle moves fine, but atmospheric pressure never moves it more than 1/2" in either direction. Any ideas?

http://www.imagestation.com/picture/sraid38/p2e617ab4fcbdbe101112ee9c588045c6/fd11c5e4.jpg

ACB
11-07-2002, 07:34 PM
It's probably fine!

Check the reading against a weather report for your locality (remember to correct for altitude, if you are not at sea level). If it is wrong, adjust it using the adjustment screw at the back.

Really, the only thing that can go wrong with an aneroid barometer is corrosion of the bellows allowing air into the vacuum chamber, in which case it won't work at all. Remember that pressure changes are usually quite small - 1/2" is plenty for most weather.

gunnar I am
11-07-2002, 07:40 PM
ACB:I hadn't checked to see if it corresponded with weather broadcasts.I'll need to do the cent. to inches conversion .I just assumed something was wrong because it moved so little.I couldn't check the bellows because the back is soldered on and the front rolled over the glass.Hope your weather is Bestandig and you got no Sturms on the way!

ACB
11-07-2002, 08:46 PM
Gunnar - you probably get weather reports giving pressure in millibars as well as inches - the millibars are centimetres of mercury, so no need to convert. I have a little Victorian pocket barometer which doubles as an altimeter, with a revolving bezel, so if you tell me your height above sea level in feet I can read off the correction to apply for you!

pwilling
11-08-2002, 01:18 PM
call your local general aviation airport and they will have an aviation weather report (very detailed) on a recording -- you can check your "altimeter" any time you want, corrected for the diff between your elevation and the airport.

I made a table with readings in all the units I could think of -- in. Hg, Mb, Kpa . . . I listen to the marine weather broadcasts in these parts and hear all three in the same broadcast. I'll send you a copy if you like

pwilling
11-08-2002, 01:21 PM
oh and there are other things that can go wrong with them, e.g. linkages between the bellows and the indicator. Usually a tiny chain on a shaft. Hard to fix on a cheap one, which is often identifiable by the ease of access to the guts of the instrument. Good luck -- I hope yours works fine and just needs to be adjusted.

Bruce Hooke
11-08-2002, 02:21 PM
I have a barometer with a very similar mechanism (except it is possible to get inside mine) and it has never really been that accurate. It goes up and down with the barometer at the local airport but it doesn't go as far up or down as it should. It still gives me a good idea for of what direction the pressure is headed and roughly how quickly.

I'd be surprised if you could move it more than 1/2" in either direction by sucking air out of the back or blowing into the back. Air actually weighs quite a bit and it is also quite possible that there is some air leakage around the glass. As far as getting into the inside - on mine you come in from the front by unscrewing the metal ring that holds the glass - do you check to see if that might work on yours. If you can get inside be careful of the lettering on the glass. I tried to clean mine and discovered that windex lifted the 'ink' :mad: Fortunately I saw what was going on before I did too much damage.

So, what I would do is go to Weather Underground (http://www.wunderground.com/cgi-bin/findweather/getForecast?query=staatsburg+ny) for your area and set the barometer to match what it says and then check every day or so to see how closely your barometer tracks with the one posted on Weather Underground. Of course if the pressure is changing VERY quickly then there may be a small difference between the reading on Weather Underground and the reading from the airport but right now there is only 0.03" difference between Poughkeepsie, NY and Providence, RI...

Remember that as far as the conversion goes you are simply converting centimeters to inches so 1" = 2.54 cm.

Bruce Hooke
11-08-2002, 02:23 PM
I did have one problem with mine where the rivits holding one side of the big spring corroded and broke off. I was able to open it up and replace the rivets with minature brass bolts...