ASTM D3631-99(2017)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D3631 − 99 (Reapproved 2017)
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 priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. Specific safety
1.1 These test methods cover the measurement of atmo-
precautionary statements are given in Section 7.
spheric pressure with two types of barometers: the Fortin-type
1.7 This international standard was developed in accor-
mercurial barometer and the aneroid barometer.
dance with internationally recognized principles on standard-
1.2 In the absence of abnormal perturbations, atmospheric
ization established in the Decision on Principles for the
pressure measured by these test methods at a point is valid
Development of International Standards, Guides and Recom-
everywherewithinahorizontaldistanceof100mandavertical
mendations issued by the World Trade Organization Technical
distance of 0.5 m of the point.
Barriers to Trade (TBT) Committee.
1.3 Atmospheric pressure decreases with increasing height
2. Referenced Documents
and varies with horizontal distance by 1 Pa/100 m or less
2.1 ASTM Standards:
except in the event of catastrophic phenomena (for example,
tornadoes). Therefore, extension of a known barometric pres- D1356Terminology Relating to Sampling and Analysis of
Atmospheres
sure to another site beyond the spatial limits stated in 1.2 can
be accomplished by correction for height difference if the D3249Practice for General Ambient Air Analyzer Proce-
dures
following criteria are met:
1.3.1 The new site is within 2000 m laterally and 500 m IEEE/ASTMSI 10Standard for Use of the International
System of Units (SI): The Modern Metric System
vertically.
1.3.2 Thechangeofpressureduringtheprevious10minhas
3. Terminology
been less than 20 Pa.
3.1 Pressure for meteorological use has been expressed in a
Thepressure,P atSite2isafunctionoftheknownpressure
P at Site 1, the algebraic difference in height above sea level, number of unit systems including inches of mercury, millime-
tres of mercury, millibars, and others less popular. These test
h − h , and the average absolute temperature in the space
1 2
between. The functional relationship between P and P is methodswilluseonlytheInternationalSystemofUnits(SI),as
1 2
described in IEEE/ASTMSI 10.
shown in 10.2.The difference between P and P for each 1 m
1 2
ofdifferencebetweenh andh isgiveninTable1and10.4for 3.1.1 Much of the apparatus in use and being sold reads in
1 2
other than SI units, so for the convenience of the user the
selected values of P and average temperature.
following conversion factors and error equivalents are given.
1.4 Atmosphericpressurevarieswithtime.Thesetestmeth-
3.1.1.1 The standard for pressure (force per unit area) is the
ods provide instantaneous values only.
pascal (Pa).
1.5 The values stated in SI units are to be regarded as
3.1.1.2 One standard atmosphere at standard gravity
standard. No other units of measurement are included in this
(9.80665 m/s ) is a pressure equivalent to:
standard.
29.9213 in. Hg at 273.15 K
760.000 mm Hg at 273.15 K
1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the 1013.25 millibars
14.6959 lbf/in.
responsibility of the user of this standard to establish appro-
101325 Pa or 101.325 kPa
These test methods are under the jurisdiction ofASTM Committee D22 on Air
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 March 1, 2017. Published March 2017. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1977. Last previous edition approved in 2011 as D3631–99 (2011). Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/D3631-99R17. the ASTM website.
Copyright ©ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA19428-2959. United States
D3631 − 99 (2017)
TABLE 1 Selected Values
6. Apparatus
Pressure P,Pa
Average 1
6.1 Fortin Barometer, which is a mercurial barometer con-
Temperature,
110 000 100 000 90 000 80 000 70 000
sisting of a glass tube containing mercury with an adjustable
T 1T
1 2
Correction to P , Pa/m, positive if h > h, negative if h < h
1 1 1 2
cisternandanindexpointerprojectingdownwardfromtheroof
230 16 15 13 12 10
of the cistern. The mercury level may be raised or lowered by
240 16 14 13 11 10
turning an adjustment screw beneath the cistern.
250 15 14 12 11 10
260 14 13 12 11 9
6.1.1 To provide acceptable measurements, the specifica-
270 14 13 11 10 9
tions of 6.1.2 – 6.1.11 must be met.
280 13 12 11 10 9
290 13 12 11 9 8
6.1.2 Maximum error at 100 000 Pa 6 30 Pa.
300 13 11 10 9 8
6.1.2.1 Maximum error at any other pressure for a barom-
310 12 11 10 9 8
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
exceed 650 Pa.
3.1.1.3 1 Pa is equivalent to: 6.1.3 Difference between errors over an interval of 10 000
Pa or less 630 Pa.
0.000295300 in. Hg at 273.15 K
0.00750062 mm Hg at 273.15 K
6.1.4 Accuracy must not deteriorate by more than 650 Pa
0.01000000 millibars over a period of a year.
0.000145037 lbf/in.
6.1.5 It must be transportable without loss of accuracy.
0.000009869 standard atmospheres
6.1.6 A mercurial barometer must be able to operate at
ambienttemperaturesrangingfrom253to333K(−20to60°C)
3.2 standard gravity—as adopted by the International Com-
and must not be exposed to temperatures below 253 K
mittee on Weights and Measures, an acceleration of 9.80665
(−38°C). It must be able to operate over ambient relative
m/s (see10.1.3).
humidities ranging from 0 to 100%.
3.3 The definitions of all other terms used in these test
6.1.7 A thermometer with a resolution of 0.11 K and a
methods can be found in Terminology D1356 and Practice
precisionandaccuracyof0.05Kmustbeattachedtothebarrel
D3249.
of the barometer.
6.1.8 The actual temperature for which the scale of a
4. Summary of Test Methods
mercury barometer is designed to give true readings (at
4.1 The instantaneous atmospheric pressure is measured
standard gravity) must be engraved on the barometer.
with two types of barometers.
6.1.9 If the evacuated volume above the mercury column
4.2 Test Method A utilizes a Fortin mercurial barometer.
can be pumped, the head vacuum must be measured with a
The mercury barometer has the advantage of being fundamen-
gauge such as a McLeod gauge or a thermocouple gauge and
tal in concept and direct in response. The disadvantages of the
reduced to 10 Pa or less.
mercury barometer are the more laborious reading procedure
6.1.10 The meniscus of a mercurial barometer must not be
than the aneroid barometer, and the need for temperature
flat.
correction.
6.1.11 The axis of the tube must be vertical (that is, aligned
with the local gravity vector).
4.3 Test Method B utilizes an aneroid barometer. The
aneroid barometer has the advantages of simplicity of reading,
6.2 Precisionaneroidbarometer,consistingofanevacuated
absence of mercury, no need for temperature compensation by
elastic capsule coupled through mechanical, electrical, or
the observer, and easy detection of trend of change. The main
optical linkage to an indicator.
disadvantages of the aneroid barometer are that it is not
6.2.1 To provide acceptable measurements, an aneroid ba-
fundamental in concept as the mercury barometer, and it
rometer must meet the specifications of 6.2.2 – 6.2.7.
requires calibration periodically against a mercury barometer.
6.2.2 Resolution of 50 Pa or less.
6.2.3 Precision of 650 Pa.
5. Significance and Use
6.2.4 Accuracy of 650 Pa root mean square error with a
5.1 Atmospheric pressure is one of the basic variables used
maximum observed error not to exceed 150 Pa throughout the
by meteorologists to describe the state of the atmosphere.
calibration against a basic standard.
5.2 The measurement of atmospheric pressure is needed
6.2.5 Temperature compensation must be included to pre-
when differences from “standard” pressure conditions must be
vent a change in reading of more than 50 Pa for a change of
accounted for in some scientific and engineering applications
temperature of 30 K.
involving pressure dependent variables.
6.2.6 Theaccuracymustnotdeterioratebymorethan 6100
Pa over a period of a year.
5.3 These test methods provide a means of measuring
atmospheric pressure with the accuracy and precision compa- 6.2.7 Thehysteresismustbesufficientlysmalltoensurethat
rable to the accuracy and precision of measurements made by thedifferenceinreadingbeforea5000-Papressurechangeand
governmental meteorological agencies. after return to the original value does not exceed 50 Pa.
D3631 − 99 (2017)
6.3 StaticPressureHead—Atmosphericpressure-measuring
d = inside diameter of the tubing, m.
instruments may be installed inside an enclosed space. The
Whenthiscalculationismadetheminimumallowableinside
pressure in the space must, however, be directly coupled to the
diameter will frequently be 5 mm or less. It is often more
pressure of the free atmosphere and not artificially affected by
convenient to use tubing larger than this size, and use of such
heating, ventilating, or air-conditioning equipment, or by the
larger tubing enhances the value of the static head and makes
dynamic effects of wind passage.
it applicable to a wider range of temperatures and pressures.
6.3.1 The Manual of Barometry (1) describes these effects.
For barometers with a static port they can be overcome with a
7. Safety Precautions
staticpressurevent,suchasthatdescribedbyGill (2),mounted
7.1 Warning—Mercury is a hazardous substance that can
outside and beyond the influence of the building. It is practical
causeillnessanddeath.Inhalationofmercuryvaporisahealth
to consider an external static vent installation if and only if the
hazard, even in small quantities. Prolonged exposure can
pressure in the building differs by more than 30 Pa from true
produce serious mental and physical impairment. Mercury can
pressure. The pressure difference due to a ventilating or air
also be absorbed through the skin, so avoid direct contact.The
conditioning system, or both can be determined from pressure
effects are cumulative.
readings taken with a precision aneroid barometer inside and
outside the building on calm days when the ventilating and air 7.2 Store mercury in closed, shatter-proof non-metallic
conditioning system is in operation. The existence of pressure containers to control its evaporation.
errors due to the dynamic effects of wind on the building can
7.3 Donotstoreorattempttooperateamercurialbarometer
often be diagnosed by careful observation of a fast response
at temperatures below 235 K (–38°C), the freezing point of
barometer in the building during periods of gusty winds.
mercury.
6.3.2 The significant pressure field near a building in wind
7.4 Work with mercury only in well-ventilated spaces,
can extend to a height of 2.5 times the height of the building
preferably under a fume hood or similar device. Use non-
and to a horizontal distance up to 10 times the height of the
permeable rubber gloves at all times and wash hands immedi-
building to the leeward. It may be impractical to locate a static
ately after any operation involving mercury. Exercise extreme
ventbeyondthisfieldbutthefollowingconsiderationsmustbe
care to avoid spilling mercury. Minimize the effect of spills by
made:
working above a large shallow pan.
6.3.2.1 The static vent must not be located on a side of the
building;
7.5 Mercurial barometers should be installed only where
6.3.2.2 The distance from the building must be as large as there is adequate ventilation. The floor beneath a mercurial
practical;
barometer should be impermeable.
6.3.2.3 The length of the tube connecting the vent to the
7.6 In a mercurial barometer, a broken tube, cistern, or bag
barometer must be minimized;
will release mercury. Immediately clean up any spills using
6.3.2.4 Toavoidblockages,averticalrunofconnectingtube
procedures recommended explicitly for mercury. Carefully
is preferable to a horizontal run; and
collect, place, and seal all spilled mercury in an appropriate
6.3.2.5 The connecting tube system must include moisture
container. Do not re-use; dispose of spilled mercury and
traps and drainage slopes on horizontal runs.
mercury contaminated materials in a safe, environmentally
6.3.3 The tubing used to connect the vent to the barometer
acceptable manner.
hasaminimumallowableinternaldiameterthatisafunctionof
the ambient static pressure, the volume of the air chambers
8. Calibration and Standardization
associated with the instrument making the pressure
8.1 A barometer is calibrated by comparing it with a
measurement, the length of the tube between the static head
secondarystandardtraceabletooneoftheprimarystandardsat
and the barometer, the viscosity of the air in the tubing and
locations listed in Table 2.
connectedequipment.Thetimelagconstantmustnotexceed1
8.2 For the United States, this standard is maintained by the
s so that for pressure and temperature of the zero pressure
National Institute of Standards and Technology.
altitudeinthestandardatmosphere,theinsidediameterdofthe
tubing connecting the static pressure head with the barometer
8.3 Except in the case of catastrophic phenomena (for
must be such that
example, tornadoes) the horizontal pressure gradient at the
29 ¼
d. 7.21 310m LV (1) earth’s surface is less than 1 Pa/100 m so that the pressure at
~ !
two instruments within 100 m of each other horizontally will
where:
not differ by an amount large enough to measure with instru-
L = length of the tube, m,
ments suggested for this test method. Instruments separated by
V = volume of the air capacity of the pressure responsive
averticaldistanceoflessthan0.5mmaybecomparedwithout
instrument and any connected air chambers within the
correcting for height difference.
system together with one half the volume of the tubing,
8.3.1 Calibration of one or more barometers that do not
m , and
produce mutual interference with the sta
...