Google 'Standard Atmosphere'. You can then find the formula to compute atmospheric pressure for any height. HTH Vic ___________________________________________________ Vic Fraenckel KC2GUI victorf AT windreader DOT com "People sleep peacefully in their beds at night only because rough men stand ready to do violence on their behalf." George Orwell ----- Original Message ----- From: "Bill & Pookie" To: "Microcontroller discussion list - Public." Sent: Wednesday, June 01, 2005 10:27 AM Subject: Re: [EE] Atmospheric Pressure Ranges > The gentleman who was going to look at his altimeter in his plane may have > the best information. I assume that the instrument would be adjustable to > any pressure at any airport prior to starting a flight. So the range of > adjustment would cover all "flying" weather. > > Bill > > ----- Original Message ----- > From: "Peter" > To: "Microcontroller discussion list - Public." > Sent: Wednesday, June 01, 2005 6:58 AM > Subject: Re: [EE] Atmospheric Pressure Ranges > > >> >> On Tue, 31 May 2005, Mike Hord wrote: >> >> > I'm trying to get a feel for the "normal" range of atmospheric >> > pressure. >> > >> > Wikipedia tells me that the highest and lowest ever recorded >> > barometric pressures are 108.57 kPa and 86.996 kPa, >> > respectively. It also tells me that "standard" atmospheric >> > pressure is 101.325 kPa. What it does NOT tell me (nor >> > does anywhere else) is what the "normal" range is; that is, >> > if a good, strong thunderstorm passes through, what can >> > I expect the pressure to be? Likewise, in a typical high >> > pressure area, what can I expect the pressure to be? >> >> It depends at what altitude you are. >> >> > I'm trying to develop a water depth gauge, and if possible, >> > I'd like to get some feel for the variation of pressure based >> > on atmospheric variations. The highest to lowest cited >> > above would represent a 2.2 meter(!) fluctuation in the >> > depth of a body of water, if one were basing the depth on >> > the pressure at the bottom. Needless to say, that >> > kind of variation would render the information useless. >> >> Pressure based depth gauges use a differential transducer. One end is >> exposed to the air. This removes the problem you describe and adds the >> problem of having two tube openings to keep clean. >> >> > Normal diurnal cycles are <.5 kPa, which corresponds >> > to approximately 5 cm of water depth. No info on >> > typical changes outside those variations, however. >> > >> > Differential measurement is NOT an option for this >> > application. >> >> You can measure depth pretty accurately using ultrasound from below. The >> water/air interface bounces it back strongly. But if you have waves it >> will be hard anyway. >> >> Peter >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > > > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist