ASTM D3631-99(2007)
(Test Method)Standard Test Methods for Measuring Surface Atmospheric Pressure
Standard Test Methods for Measuring Surface Atmospheric Pressure
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 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.
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Designation:D3631–99 (Reapproved 2007)
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- D1356 Terminology Relating to Sampling and Analysis of
rial barometer and the aneroid barometer. Atmospheres
1.2 In the absence of abnormal perturbations, atmospheric D3249 Practice for General Ambient Air Analyzer Proce-
pressure measured by these methods at a point is valid dures
everywherewithinahorizontaldistanceof100mandavertical IEEE/ASTMSI 10 Standard for Use of the International
distance of 0.5 m of the point. System of Units (SI): The Modern Metric System
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,
tornadoes). Therefore, extension of a known barometric pres- number of unit systems including inches of mercury, millime-
tres of mercury, millibars, and others less popular. These
sure to another site beyond the spatial limits stated in 1.2 can
be accomplished by correction for height difference if the methodswilluseonlytheInternationalSystemofUnits(SI),as
described in IEEE/ASTMSI 10.
following criteria are met:
1.3.1 The new site is within 2000 m laterally and 500 m 3.1.1 Much of the apparatus in use and being sold reads in
other than SI units, so for the convenience of the user the
vertically.
1.3.2 Thechangeofpressureduringtheprevious10minhas following conversion factors and error equivalents are given.
3.1.1.1 The standard for pressure (force per unit area) is the
been less than 20 Pa.
Thepressure,P atSite2isafunctionoftheknownpressure pascal (Pa).
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
between. The functional relationship between P and P is 29.9213 in. Hg at 273.15 K
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
ofdifferencebetweenh andh isgiveninTable1and10.4for 1013.25 millibars
1 2
14.6959 lbf/in.
selected values of P and average temperature.
1.4 Atmospheric pressure varies with time. These methods 101325 Pa or 101.325 kPa
3.1.1.3 1 Pa is equivalent to:
provide instantaneous values only.
1.5 The values stated in SI units are to be regarded as the 0.000295300 in. Hg at 273.15 K
0.00750062 mm Hg at 273.15 K
standard.
1.6 This standard does not purport to address all of the 0.01000000 millibars
0.000145037 lbf/in.
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- 0.000009869 standard atmospheres
3.2 standardgravity—asadoptedbytheInternationalCom-
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. Specific safety mittee on Weights and Measures, an acceleration of 9.80665
m/s (see10.1.3).
precautionary statements are given in Section 7.
These test methods are under the jurisdiction ofASTM Committee D22 onAir
Quality and 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, 2007. Published December 2007. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1977. Last previous edition approved in 2004 as D3631-99(2004). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/D3631-99R07. the ASTM website.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959, United States.
D3631–99 (2007)
3.3 The definitions of all other terms used in these methods 6.1.2.2 Foramarineapplicationtheerroratapointmustnot
can be found in Terminology D1356 and Practice D3249. exceed 650 Pa.
6.1.3 Difference between errors over an interval of 10 000
Pa or less 630 Pa.
TABLE 1 Selected Values
6.1.4 Accuracy must not deteriorate by more than 650 Pa
Average Pressure P,Pa
over a period of a year.
Tempera-
110 000 100 000 90 000 80 000 70 000
ture, 6.1.5 It must be transportable without loss of accuracy.
T 1 T
1 2
Correction to P , Pa/m, positive if h > h, negative if h < h
6.1.6 A mercurial barometer must be able to operate at
1 1 1 2
ambienttemperaturesrangingfrom253to333K(−20to60°C)
230 16 15 13 12 10
240 16 14 13 11 10
and must not be exposed to temperatures below 253 K
250 15 14 12 11 10
(−38°C). It must be able to operate over ambient relative
260 14 13 12 11 9
humidities ranging from 0 to 100%.
270 14 13 11 10 9
280 13 12 11 10 9
6.1.7 A thermometer with a resolution of 0.11 K and a
290 13 12 11 9 8
precisionandaccuracyof0.05Kmustbeattachedtothebarrel
300 13 11 10 9 8
of the barometer.
310 12 11 10 9 8
6.1.8 The actual temperature for which the scale of a
mercury barometer is designed to give true readings (at
standard gravity) must be engraved on the barometer.
4. Summary of Methods
6.1.9 If the evacuated volume above the mercury column
4.1 The instantaneous atmospheric pressure is measured
can be pumped, the head vacuum must be measured with a
with two types of barometers.
gauge such as a McLeod gauge or a thermocouple gauge and
4.2 Method A utilizes a Fortin mercurial barometer. The
reduced to 10 Pa or less.
mercury barometer has the advantage of being fundamental in
6.1.10 The meniscus of a mercurial barometer must not be
concept and direct in response. The disadvantages of the
flat.
mercury barometer are the more laborious reading procedure
6.1.11 The axis of the tube must be vertical (that is, aligned
than the aneroid barometer, and the need for temperature
with the local gravity vector).
correction.
6.2 Precisionaneroidbarometer,consistingofanevacuated
4.3 Method B utilizes an aneroid barometer. The aneroid
elastic capsule coupled through mechanical, electrical, or
barometerhastheadvantagesofsimplicityofreading,absence
optical linkage to an indicator.
of mercury, no need for temperature compensation by the
6.2.1 To provide acceptable measurements, an aneroid ba-
observer, and easy detection of trend of change. The main
rometer must meet the specifications of 6.2.2-6.2.7.
disadvantages of the aneroid barometer are that it is not
6.2.2 Resolution of 50 Pa or less.
fundamental in concept as the mercury barometer, and it
6.2.3 Precision of 650 Pa.
requires calibration periodically against a mercury barometer.
6.2.4 Accuracy of 650 Pa root mean square error with a
maximum observed error not to exceed 150 Pa throughout the
5. Significance and Use
calibration against a basic standard.
5.1 Atmospheric pressure is one of the basic variables used
6.2.5 Temperature compensation must be included to pre-
by meteorologists to describe the state of the atmosphere.
vent a change in reading of more than 50 Pa for a change of
5.2 The measurement of atmospheric pressure is needed
temperature of 30 K.
when differences from “standard” pressure conditions must be
6.2.6 Theaccuracymustnotdeterioratebymorethan 6100
accounted for in some scientific and engineering applications
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 Static Pressure Head—Atmospheric pressure-
mental meteorological agencies.
measuring instruments may be installed inside an enclosed
space. The pressure in the space must, however, be directly
6. Apparatus
coupled to the pressure of the free atmosphere and not
6.1 Fortin Barometer, which is a mercurial barometer con-
artificially affected by heating, ventilating, or air-conditioning
sisting of a glass tube containing mercury with an adjustable
equipment, or by the 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.
6.1.2.1 Maximum error at any other pressure for a barom-
eter whose range: (a) does not extend below 80 000 Pa 6 50
Boldface numbers in parentheses refer to references at the end of these
Pa (b) extends below 80 000 Pa 6 80 Pa. methods.
D3631–99 (2007)
pressure in the building differs by more than 30 Pa from true 7.2 Store mercury in closed, shatter-proof non-metallic
pressure. The pressure difference due to a ventilating or air containers to control its evaporation.
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
working above a large shallow pan.
can extend to a height of 2.5 times the height of the building
and to a horizontal distance up to 10 times the height of the 7.5 Mercurial barometers should be installed only where
there is adequate ventilation. The floor beneath a mercurial
building to the leeward. It may be impractical to locate a static
ventbeyondthisfieldbutthefollowingconsiderationsmustbe barometer should be impermeable.
7.6 In a mercurial barometer, a broken tube, cistern, or bag
made:
will release mercury. Immediately clean up any spills using
6.3.2.1 The static vent must not be located on a side of the
procedures recommended explicitly for mercury. Carefully
building;
collect, place, and seal all spilled mercury in an appropriate
6.3.2.2 The distance from the building must be as large as
container. Do not re-use; dispose of spilled mercury and
practical;
mercury contaminated materials in a safe, environmentally
6.3.2.3 The length of the tube connecting the vent to the
acceptable manner.
barometer must be minimized;
6.3.2.4 Toavoidblockages,averticalrunofconnectingtube
8. Calibration and Standardization
is preferable to a horizontal run; and
8.1 A barometer is calibrated by comparing it with a
6.3.2.5 The connecting tube system must include moisture
secondarystandardtraceabletooneoftheprimarystandardsat
traps and drainage slopes on horizontal runs.
locations listed in Table 2.
6.3.3 The tubing used to connect the vent to the barometer
8.2 For the United States this standard is maintained by the
hasaminimumallowableinternaldiameterthatisafunctionof
National Institute of Standards and Technology, Gaithersburg,
the ambient static pressure, the volume of the air chambers
MD 20899.
associated with the instrument making the pressure measure-
8.3 Except in the case of catastrophic phenomena (for
ment, the length of the tube between the static head and the
example, tornadoes) the horizontal pressure gradient at the
barometer, the viscosity of the air in the tubing and connected
earth’s surface is less than 1 Pa/100 m so that the pressure at
equipment. The time lag constant must not exceed1sso that
two instruments within 100 m of each other horizontally will
forpressureandtemperatureofthezeropressurealtitudeinthe
not differ by an amount large enough to measure with instru-
standard atmosphere, the inside diameter d of the tubing
ments suggested for this method. Instruments separated by a
connectingthestaticpressureheadwiththebarometermustbe
vertical distance of less than 0.5 m may be compared without
such that
correcting for height difference.
29 ¼
d . ~7.21 310m LV! (1)
where:
TABLE 2 Regional Standard Barometers
L = length of the tube, m,
Region Location Category
V = volume of the air capacity of the pressure responsive
I Pretoria, South Africa A
r
instrument and any connected air chambers within the
II Calcutta, India B
r
system together with one half the volume of the
III Rio de Janeiro, Brazil A
r
Buenos Aires,Argentina B
r
tubing, m , and
Maracay, Venezuela B
r
d = inside diameter of the tubing, m.
IV Washington, DC, A
r
Whenthiscalculationismadetheminimumallowableinside (Gaithersburg, Md.), USA
V Melbourne,Australia A
r
diameter will frequently be 5 mm or less. It is often more
VI London, United Kingdom A
r
convenient to use tubing larger than this size, and use of such
Leningrad, U.S.S.R. A
r
larger tubing enhances the value of the static head and makes Paris, France A
r
Hamburg, Federal Republic of A
r
it applicable to a wider range of temperatures and pressures.
Germany
A—Abarometer that has been selected by regional agreement as a reference
r
7. Safety Precautions
standard for barometers of that region and is capable of independent determina-
tion of pressure to an accuracy of 65 Pa.
7.1 Warning: Mercury is a hazardous substance that can
B—Aworkingstandardbarometerwithknownerrorsestablishedbycomparison
r
causeillnessanddeath.Inhalationofmercuryvaporisahealth
withaprimaryorsecondarystandard.Suchbarometersareusedinaregionwhere
hazard, even in small quantities. Prolonged exposure can the National meteorologica
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