ASTM D3631-99(2011)
(Test Method)Standard Test Methods for Measuring Surface Atmospheric Pressure
Standard Test Methods for Measuring Surface Atmospheric Pressure
SIGNIFICANCE AND USE
Atmospheric pressure is one of the basic variables used by meteorologists to describe the state of the atmosphere.
The measurement of atmospheric pressure is needed when differences from “standard” pressure conditions must be accounted for in some scientific and engineering applications involving pressure dependent variables.
These methods provide a means of measuring atmospheric pressure with the accuracy and precision comparable to the accuracy and precision of measurements made by governmental meteorological agencies.
SCOPE
1.1 These methods cover the measurement of atmospheric pressure with two types of barometers: the Fortin-type mercurial barometer and the aneroid barometer.
1.2 In the absence of abnormal perturbations, atmospheric pressure measured by these methods at a point is valid everywhere within a horizontal distance of 100 m and a vertical distance of 0.5 m of the point.
1.3 Atmospheric pressure decreases with increasing height and varies with horizontal distance by 1 Pa/100 m or less except in the event of catastrophic phenomena (for example, tornadoes). Therefore, extension of a known barometric pressure to another site beyond the spatial limits stated in 1.2 can be accomplished by correction for height difference if the following criteria are met:
1.3.1 The new site is within 2000 m laterally and 500 m vertically.
1.3.2 The change of pressure during the previous 10 min has been less than 20 Pa.
The pressure, P2 at Site 2 is a function of the known pressure P1 at Site 1, the algebraic difference in height above sea level, h1 − h 2, and the average absolute temperature in the space between. The functional relationship between P1 and P2 is shown in 10.2. The difference between P1 and P2 for each 1 m of difference between h1 and h2 is given in Table 1 and 10.4 for selected values of P1 and average temperature.
1.4 Atmospheric pressure varies with time. These methods provide instantaneous values only.
1.5 The values stated in SI units are to be regarded as the standard.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Specific safety precautionary statements are given in Section 7.
TABLE 1 Selected Values Average
Tempera-
ture,
Pressure P1, Pa 110 000100 00090 00080 00070 000 Correction to P1, Pa/m, positive if h1 > h, negative if h1 h2 230 1615131210 240 1614131110 250 1514121110 260 14131211 9 270 14131110 9 280 13121110 9 290 131211 9 8 300 131110 9 8 310 121110 9 8
General Information
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Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D3631 − 99 (Reapproved 2011)
Standard Test Methods for
Measuring Surface Atmospheric Pressure
This standard is issued under the fixed designation D3631; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 2. Referenced Documents
1.1 These methods cover the measurement of atmospheric 2.1 ASTM Standards:
pressure with two types of barometers: the Fortin-type mercu- D1356Terminology Relating to Sampling and Analysis of
rial barometer and the aneroid barometer. Atmospheres
D3249Practice for General Ambient Air Analyzer Proce-
1.2 In the absence of abnormal perturbations, atmospheric
dures
pressure measured by these methods at a point is valid
IEEE/ASTMSI 10Standard for Use of the International
everywherewithinahorizontaldistanceof100mandavertical
System of Units (SI): The Modern Metric System
distance of 0.5 m of the point.
1.3 Atmospheric pressure decreases with increasing height
3. Terminology
and varies with horizontal distance by 1 Pa/100 m or less
3.1 Pressure for meteorological use has been expressed in a
except in the event of catastrophic phenomena (for example,
number of unit systems including inches of mercury, millime-
tornadoes). Therefore, extension of a known barometric pres-
tres of mercury, millibars, and others less popular. These
sure to another site beyond the spatial limits stated in 1.2 can
methodswilluseonlytheInternationalSystemofUnits(SI),as
be accomplished by correction for height difference if the
described in IEEE/ASTMSI 10.
following criteria are met:
3.1.1 Much of the apparatus in use and being sold reads in
1.3.1 The new site is within 2000 m laterally and 500 m
other than SI units, so for the convenience of the user the
vertically.
following conversion factors and error equivalents are given.
1.3.2 Thechangeofpressureduringtheprevious10minhas
3.1.1.1 The standard for pressure (force per unit area) is the
been less than 20 Pa.
pascal (Pa).
Thepressure,P atSite2isafunctionoftheknownpressure
3.1.1.2 One standard atmosphere at standard gravity
P at Site 1, the algebraic difference in height above sea level,
(9.80665 m/s ) is a pressure equivalent to:
h − h , and the average absolute temperature in the space
1 2
29.9213 in. Hg at 273.15 K
between. The functional relationship between P and P is
1 2
760.000 mm Hg at 273.15 K
shown in 10.2.The difference between P and P for each 1 m
1 2
1013.25 millibars
ofdifferencebetweenh andh isgiveninTable1and10.4for
1 2
14.6959 lbf/in.
selected values of P and average temperature.
101325 Pa or 101.325 kPa
1.4 Atmospheric pressure varies with time. These methods
3.1.1.3 1 Pa is equivalent to:
provide instantaneous values only.
0.000295300 in. Hg at 273.15 K
0.00750062 mm Hg at 273.15 K
1.5 The values stated in SI units are to be regarded as the
0.01000000 millibars
standard.
0.000145037 lbf/in.
1.6 This standard does not purport to address all of the
0.000009869 standard atmospheres
safety concerns, if any, associated with its use. It is the
3.2 standard gravity—as adopted by the International Com-
responsibility of the user of this standard to establish appro-
mittee on Weights and Measures, an acceleration of 9.80665
priate safety and health practices and determine the applica-
m/s (see10.1.3).
bility of regulatory limitations prior to use. Specific safety
precautionary statements are given in Section 7.
3.3 The definitions of all other terms used in these methods
can be found in Terminology D1356 and Practice D3249.
These test methods are under the jurisdiction ofASTM Committee D22 on Air
Qualityand are the direct responsibility of Subcommittee D22.11 on Meteorology. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Oct. 1, 2011. Published October 2011. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1977. Last previous edition approved in 2007 as D3631-99(2007). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/D3631-99R11. the ASTM website.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959. United States
D3631 − 99 (2011)
TABLE 1 Selected Values
6.1.3 Difference between errors over an interval of 10 000
Average Pa or less 630 Pa.
Pressure P,Pa
Tempera-
6.1.4 Accuracy must not deteriorate by more than 650 Pa
110 000 100 000 90 000 80 000 70 000
ture,
over a period of a year.
T 1T
1 2
Correction to P , Pa/m, positive if h > h, negative if h < h
1 1 1 2
2 6.1.5 It must be transportable without loss of accuracy.
230 16 15 13 12 10
6.1.6 A mercurial barometer must be able to operate at
240 16 14 13 11 10
ambienttemperaturesrangingfrom253to333K(−20to60°C)
250 15 14 12 11 10
260 14 13 12 11 9
and must not be exposed to temperatures below 253 K
270 14 13 11 10 9
(−38°C). It must be able to operate over ambient relative
280 13 12 11 10 9
humidities ranging from 0 to 100%.
290 13 12 11 9 8
300 13 11 10 9 8
6.1.7 A thermometer with a resolution of 0.11 K and a
310 12 11 10 9 8
precisionandaccuracyof0.05Kmustbeattachedtothebarrel
of the barometer.
6.1.8 The actual temperature for which the scale of a
4. Summary of Methods
mercury barometer is designed to give true readings (at
standard gravity) must be engraved on the barometer.
4.1 The instantaneous atmospheric pressure is measured
6.1.9 If the evacuated volume above the mercury column
with two types of barometers.
can be pumped, the head vacuum must be measured with a
4.2 Method A utilizes a Fortin mercurial barometer. The
gauge such as a McLeod gauge or a thermocouple gauge and
mercury barometer has the advantage of being fundamental in
reduced to 10 Pa or less.
concept and direct in response. The disadvantages of the
6.1.10 The meniscus of a mercurial barometer must not be
mercury barometer are the more laborious reading procedure
flat.
than the aneroid barometer, and the need for temperature
6.1.11 The axis of the tube must be vertical (that is, aligned
correction.
with the local gravity vector).
4.3 Method B utilizes an aneroid barometer. The aneroid
6.2 Precisionaneroidbarometer,consistingofanevacuated
barometerhastheadvantagesofsimplicityofreading,absence
elastic capsule coupled through mechanical, electrical, or
of mercury, no need for temperature compensation by the
optical linkage to an indicator.
observer, and easy detection of trend of change. The main
6.2.1 To provide acceptable measurements, an aneroid ba-
disadvantages of the aneroid barometer are that it is not
rometer must meet the specifications of 6.2.2-6.2.7.
fundamental in concept as the mercury barometer, and it
6.2.2 Resolution of 50 Pa or less.
requires calibration periodically against a mercury barometer.
6.2.3 Precision of 650 Pa.
6.2.4 Accuracy of 650 Pa root mean square error with a
5. Significance and Use
maximum observed error not to exceed 150 Pa throughout the
5.1 Atmospheric pressure is one of the basic variables used
calibration against a basic standard.
by meteorologists to describe the state of the atmosphere.
6.2.5 Temperature compensation must be included to pre-
5.2 The measurement of atmospheric pressure is needed vent a change in reading of more than 50 Pa for a change of
temperature of 30 K.
when differences from “standard” pressure conditions must be
accounted for in some scientific and engineering applications 6.2.6 Theaccuracymustnotdeterioratebymorethan 6100
Pa over a period of a year.
involving pressure dependent variables.
6.2.7 Thehysteresismustbesufficientlysmalltoensurethat
5.3 These methods provide a means of measuring atmo-
thedifferenceinreadingbeforea5000-Papressurechangeand
sphericpressurewiththeaccuracyandprecisioncomparableto
after return to the original value does not exceed 50 Pa.
the accuracy and precision of measurements made by govern-
6.3 StaticPressureHead—Atmosphericpressure-measuring
mental meteorological agencies.
instruments may be installed inside an enclosed space. The
6. Apparatus
pressure in the space must, however, be directly coupled to the
pressure of the free atmosphere and not artificially affected by
6.1 Fortin Barometer, which is a mercurial barometer con-
heating, ventilating, or air-conditioning equipment, or by the
sisting of a glass tube containing mercury with an adjustable
dynamic effects of wind passage.
cisternandanindexpointerprojectingdownwardfromtheroof
6.3.1 The Manual of Barometry (1) describes these effects.
of the cistern. The mercury level may be raised or lowered by
For barometers with a static port they can be overcome with a
turning an adjustment screw beneath the cistern.
staticpressurevent,suchasthatdescribedbyGill (2),mounted
6.1.1 To provide acceptable measurements, the specifica-
outside and beyond the influence of the building. It is practical
tions of 6.1.2-6.1.11 must be met.
to consider an external static vent installation if and only if the
6.1.2 Maximum error at 100 000 Pa 6 30 Pa.
pressure in the building differs by more than 30 Pa from true
6.1.2.1 Maximum error at any other pressure for a barom-
pressure. The pressure difference due to a ventilating or air
eter whose range: (a) does not extend below 80 000 Pa 6 50
Pa (b) extends below 80 000 Pa 6 80 Pa.
6.1.2.2 Foramarineapplicationtheerroratapointmustnot
Boldface numbers in parentheses refer to references at the end of these
exceed 650 Pa. methods.
D3631 − 99 (2011)
conditioning system, or both can be determined from pressure 7.3 Donotstoreorattempttooperateamercurialbarometer
readings taken with a precision aneroid barometer inside and at temperatures below 235 K (-38°C), the freezing point of
outside the building on calm days when the ventilating and air mercury.
conditioning system is in operation. The existence of pressure
7.4 Work with mercury only in well-ventilated spaces,
errors due to the dynamic effects of wind on the building can
preferably under a fume hood or similar device. Use non-
often be diagnosed by careful observation of a fast response
permeable rubber gloves at all times and wash hands immedi-
barometer in the building during periods of gusty winds.
ately after any operation involving mercury. Exercise extreme
6.3.2 The significant pressure field near a building in wind
care to avoid spilling mercury. Minimize the effect of spills by
can extend to a height of 2.5 times the height of the building
working above a large shallow pan.
and to a horizontal distance up to 10 times the height of the
7.5 Mercurial barometers should be installed only where
building to the leeward. It may be impractical to locate a static
there is adequate ventilation. The floor beneath a mercurial
ventbeyondthisfieldbutthefollowingconsiderationsmustbe
barometer should be impermeable.
made:
6.3.2.1 The static vent must not be located on a side of the 7.6 In a mercurial barometer, a broken tube, cistern, or bag
building; will release mercury. Immediately clean up any spills using
6.3.2.2 The distance from the building must be as large as
procedures recommended explicitly for mercury. Carefully
practical; collect, place, and seal all spilled mercury in an appropriate
6.3.2.3 The length of the tube connecting the vent to the
container. Do not re-use; dispose of spilled mercury and
barometer must be minimized; mercury contaminated materials in a safe, environmentally
6.3.2.4 Toavoidblockages,averticalrunofconnectingtube
acceptable manner.
is preferable to a horizontal run; and
8. Calibration and Standardization
6.3.2.5 The connecting tube system must include moisture
traps and drainage slopes on horizontal runs.
8.1 A barometer is calibrated by comparing it with a
6.3.3 The tubing used to connect the vent to the barometer
secondarystandardtraceabletooneoftheprimarystandardsat
hasaminimumallowableinternaldiameterthatisafunctionof
locations listed in Table 2.
the ambient static pressure, the volume of the air chambers
8.2 For the United States this standard is maintained by the
associated with the instrument making the pressure
National Institute of Standards and Technology, Gaithersburg,
measurement, the length of the tube between the static head
MD 20899.
and the barometer, the viscosity of the air in the tubing and
8.3 Except in the case of catastrophic phenomena (for
connectedequipment.Thetimelagconstantmustnotexceed1
example, tornadoes) the horizontal pressure gradient at the
s so that for pressure and temperature of the zero pressure
earth’s surface is less than 1 Pa/100 m so that the pressure at
altitudeinthestandardatmosphere,theinsidediameterdofthe
two instruments within 100 m of each other horizontally will
tubing connecting the static pressure head with the barometer
not differ by an amount large enough to measure with instru-
must be such that
ments suggested for this method. Instruments separated by a
29 ¼
d. 7.21 310m LV (1)
~ !
vertical distance of less than 0.5 m may be compared without
where:
correcting for height difference.
L = length of the tube, m,
V = volume of the air capacity of the pressure responsive
TABLE 2 Regional Standard Barometers
instrument and any connected air chambers within the
Region Location Category
system together with one half the volume of the tubing,
I Pretoria, South Africa A
r
m , and
II Calcutta, India B
r
d = inside diameter of the tubing, m.
III Rio de Janeiro, Brazil A
r
Buenos Aires,Argentina B
r
Whenthiscalculationismadetheminimumallowableinside
Maracay, Venezuela B
r
diameter will frequently be 5 mm or less. It is often more
IV Washington, DC, A
r
convenient to use tubing larger than this size, and use of such (Gaithersburg, Md.), USA
V Melbourne,Australia A
r
larger tubing enhances the value of the static head and makes
VI London, United Kingdom A
r
it applicable to a wider range of temperatures and pressures.
Leningrad, U.S.S.R. A
r
Paris, France A
r
Hamburg, Federal Republic of A
r
7. Safety Precautions
Germany
7.1 Warning—Mercury is a hazardous substance that can
A—Abarometer that has been selected by regional agreement as a reference
r
causeillnessanddeath.Inhalationofmercuryvaporisahealth
standard for barometers of that region and is capable of independent determina-
hazard, even in small quantities. Prolonged exposure can
tion of pressure to an accuracy of 65 Pa.
B—Aworkingstandardbarometerwithknownerrorsestablishedbycomparison
produce serious mental and physical impairment. Mercury can
r
withaprimaryorsecondarystandard.Suchbarometersareusedinaregionwhere
also be absorbed through the skin, so avoid direct cont
...
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