Some more research is indicated here, I was wondering if it was a hangover from
the previous FF Units where you have PSI on one side of ambient (or gauge) and
inches mercury suction on the other. The benefit of Pascals is (I believe) that
a vacuum with no pressure is zero Pascals so any indication is always positive.
Similar to Kelvin starting at Zero and always being a positive value.
Any of the Physicists on this list throw any light on this? I know there are a
lot of knowledgeable people out there on this list.
Mike Payne
----- Original Message -----
From: John M. Steele
To: U.S. Metric Association
Sent: Thursday, 09 July 2009 22:31
Subject: [USMA:45334] Re: Vacuum display
I have never noticed anything in the SI Brochure or NIST SP330
requiring pressure to be stated on an absolute basis vs gauge. Obviously the
other side is atmospheric pressure.
Since proper procedure is to purge the a/c system to a vacuum and
refill with refrigerant, absolute pressure might be a better choice here. But
in most geographic areas the flucuation in local pressure (with weather, or
even elevation above sea level) would be minor vs the accuracy of the gauge.
However, I think it is always the same gauge and they paint different
numbers on the dial face.
--- On Thu, 7/9/09, Michael Payne <[email protected]> wrote:
From: Michael Payne <[email protected]>
Subject: [USMA:45330] Vacuum display
To: "U.S. Metric Association" <[email protected]>
Date: Thursday, July 9, 2009, 3:53 PM
I was under the impression SI pressure in Pascal's was always
positive. Earth pressure near 100 kPa, Mars pressure near 20 kPa, outer space
near 0 Pa. Is this correct. I see the gauge from Yellow Jacket has an area
listing a minus side.
Mike Payne
