Date:         Sat, 11 Oct 2008 12:47:52 -0700
Reply-To:     Keith Hughes <keithahughes@QWEST.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Keith Hughes <keithahughes@QWEST.NET>
Subject:      Re: Gauges
Comments: To: Mike <mbucchino@charter.net>
In-Reply-To:  <0286838330594CB6AB819A13ABFE710D@mike2d93581d7f>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Mike wrote:
> As I said; 14.7 psi is a standard that is equal to atmopheric pressure
> when measured at sea level...................
Well, no you stated that 1 Bar = 1 ATM = 14.7 psi, which is clearly
incorrect.  Use the converter link *you* provided - it's quite simple.
1 Barg = 14.5 psig, 1 Bara = 14.5 psia.
>
> http://www.ilpi.com/msds/ref/pressureunits.html
>
> http://www.unitconversion.org/pressure/bar-conversion.html
>
> http://wiki.xtronics.com/index.php/Pressure_Conversion_Table
>
>
> P.S.I. (bara or absolute bar) is not the same as P.S.I.G. (barg or
> guage bar). The sea level standard has everything to do with guages;
Absolute is referenced to vacuum, "gauge" is referenced to ambient
pressure.  Neither has *any* relevance to the unit conversion.  1 bar
does not equal 14.7 psia.  And sea level has nothing to do with pressure
gauges - altimeters yes, that's why when you get the barometer reading
from the airport weather station, it is Not the actual atmospheric
pressure, it's the equivalent sea level pressure, corrected for local
conditions of altitude and air density.  Absolute pressure
gauges/transducers are referenced to vacuum (i.e. read 0 at full
vacuum), and gauge pressure gauges/transducers have to be calibrated to
read zero at station pressure (i.e. ambient atmospheric pressure).  At
all elevations and atmospheric pressures, ambient pressure is 0 psig.
Absolute pressure gauges/transducers, in ambient conditions, will read
the atmospheric pressure.  Here in Phoenix, ambient pressure is 0 psig,
14.15 ± psia.

Keith Hughes
'86 Westy Tiico (Marvin)