I have come by an old barometer - something like the item shown here
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(although not quite of the quality). Now I know that these devices measure atmospheric pressure, but I am not clear on how much this will be affected by the instrument location.
Does a heat source like a radiator change atmospheric pressure? Can I mount this on a wall above a radiator and expect it to work?
From my memory of the barometer, the needle doesn't appear to move much in operation. Is this because it was previously in a centrally heated house, or is there likely to be something wrong here?
No certainly not it tends to crack. Actually these are just a sealed bellows I think that operate a needle by clever gearing. If the unit is leaky though it will never work. I've not got one now but they dont seem to care where they are unless you have forced air air conditioning to keep pressure high, most houses are the same as outside. I see we are all supposed to be using Hecto Pascals now instead of Millibarrs etc. Ho hum, pass me that altimeter. Brian
Not that would be measurable by that instrument in a normal (non-air tight) house. B-)
I wouldn't, as others have said the oak won't like it and if you are getting wide temperature variations (rad on v rad off) that could affect the readings as the works expand/contract. Try an find a place with a fairly stable temperature to be kind to the wood and the instrument.
Well ATM the UK is under the influence of a high pressure and it's not changing very much at all.
Normal sort of range would be about 29.25" to 30" of mercury (1000 to
1030 mb) changing from one to the other normally over couple/three days. Though it can change faster. These type of barometers might need a gentle tap to make the needle move properly to the current pressure reading. There also ought to be a small adjustment screw to compensate for your locations altitude, so the instrument reads "sea level" pressure. Now is not a bad time to check that as most of the country is pretty much at 1032 mb (30.5" Hg)
Depending on how windy it is and how exposed/draughty your house is that can cause a few mb of reduced pressure inside by venturi effects of chimneys etc. I've noticed on several occasions when a gale suddenly stops there is a coresponding step up in the air pressure.
Location will not affect the baro, but it will affect the thermometer and possibly the wood. Don't know much of aneroids, prefer mercury. As regards movement of the needle. Set baro in desired position. Align the cursor with the hand. Repeat at 10am every day of course. Note the movement of the hand over a 24hr period. If the swing is 30 deg or more- Sun hat if up, raincoat, hat & wellies if it's down. Do you have a dinghy? Just keep an eye on it for a few days. I suspect most aneroid baros would not be repairable. TBH, they're not worth it. I think the seller of the item you show is utterly and completely off trolley. Delete the first number, divide the remainder by two and you might be in the real world. hth Nick.
The heat source doesn't change atmospheric pressure, but the pressure reading will cycle a little as the instrument temperature changes, something like 3% for a 10 degree C variation. If the needle isn't moving much it's likely that the bellows has a leak, or there is a problem in the (relatively fragile) linkage between the bellows and the needle.
Pressure is the same pressure irrespective, providing it is in the same geographical area. So mount it in any sensible location, but not over a radiator as that will affect the wood. You can calibrate it, by comparing it to your local weather station - note the pressure indicated by your instrument, at the times the pressures are suggested to be have measured, then compare your reading with what they suggest the pressure was at that paticular time. From that, you should be able to work out what your error was and make an adjustment.
Best to do it when the pressure has been steady for a good while though, when the isobars are widely spaced / not much wind.
Re the instrument itself, it measures air pressure. The only influence you have on it's reading is the altitude of your house. (Altitude also affects air pressure) Normal pressure is 1013mB.=760mm of Hg
They often don't work because the stack of capsules inside develop cracks. It is and aneroid barometer.
I did repair one I got at auction. REMARKABLY similar to that.
It turned out there was a little teeny bicycle chain inside it that connected the capsule to the pointer shaft and that was all rusted up. Some easing oil and brushing with paraffin got it all cleaned up and free, then it got some very light machine oil.
i think I had to bid against another nutter like me and i paid 85 quid.
The latter. It will almost certainly be what mine is. a teensy sprocket chain round a drum, very prone to rusting if left in a loft or a shed. I've never had the aneroid capsule itself go ..on several I have owned over the years.
the final shaft bearing may be seized too. gentle working of the mechanism and light oil gets it all back.
If a smart tap on the face doesn't cause the needle to jump, its seized in some way. If it jumps, but doesn't move with the weather, the capsule has gone.
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