ASTM D3631-99
(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 atmos- pheric pressure with two types of barometers: the Fortin-type mercurial barometer and the aneroid barometer.
1.2 In the absence of abnormal perturbations, atmos- pheric 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, P 2 at Site 2 is a function of the known pressure P 1 at Site 1, the algebraic difference in height above sea level, h 1 - h 2 , and the average absolute temperature in the space between. The functional relationship between P 1 and P 2 is shown in 10.2. The difference between P 1 and P 2 for each 1 m of difference between h 1 and h 2 is given in Table 1 and 10.4 for selected values of P 1 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: D 3631 – 99
Standard Test Methods for Measuring
Surface Atmospheric Pressure
This standard is issued under the fixed designation D 3631; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) 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- D 1356 Terminology Relating to Sampling and Analysis of
rial barometer and the aneroid barometer. Atmospheres
1.2 In the absence of abnormal perturbations, atmospheric D 3249 Practice for General Ambient Air Analyzer Proce-
pressure measured by these methods at a point is valid dures
everywhere within a horizontal distance of 100 m and a vertical IEEE/ASTM SI 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 methods will use only the International System of Units (SI), as
described in IEEE/ASTM SI 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 The change of pressure during the previous 10 min has 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.
The pressure, P at Site 2 is a function of the known pressure 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
of difference between h and h is given in Table 1 and 10.4 for 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 standard gravity—as adopted by the International Com-
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 (see 10.1.3).
precautionary statements are given in Section 7.
3.3 The definitions of all other terms used in these methods
can be found in Terminology D 1356 and Practice D 3249.
These test methods are under the jurisdiction of ASTM Committee D22 on
Sampling and Analysis of Atmospheres and are the direct responsibility of
Subcommittee D22.11 on Meteorological Measurements.
Current edition approved September 10, 1999. Published November 1999. Annual Book of ASTM Standards, Vol 11.03.
Originally pub lished as D 3631 – 77. Last previous edition D 3631 – 95. Annual Book of ASTM Standards, Vol 14.02.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D3631–99
TABLE 1 Selected Values
6.1.4 Accuracy must not deteriorate by more than 6 50 Pa
Average Pressure P ,Pa over a period of a year.
Tempera-
6.1.5 It must be transportable without loss of accuracy.
110 000 100 000 90 000 80 000 70 000
ture,
6.1.6 A mercurial barometer must be able to operate at
T 1 T
1 2
Correction to P , Pa/m, positive if h > h, negative if h < h
1 1 1 2
ambient temperatures ranging from 253 to 333 K (−20 to 60°C)
230 16 15 13 12 10
and must not be exposed to temperatures below 253 K
240 16 14 13 11 10
(−38°C). It must be able to operate over ambient relative
250 15 14 12 11 10
260 14 13 12 11 9
humidities ranging from 0 to 100 %.
270 14 13 11 10 9
6.1.7 A thermometer with a resolution of 0.11 K and a
280 13 12 11 10 9
precision and accuracy of 0.05 K must be attached to the barrel
290 13 12 11 9 8
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.
gage such as a McLeod gage or a thermocouple gage 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 Precision aneroid barometer, consisting of an evacuated
4.3 Method B utilizes an aneroid barometer. The aneroid
elastic capsule coupled through mechanical, electrical, or
barometer has the advantages of simplicity of reading, 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 6 50 Pa.
requires calibration periodically against a mercury barometer.
6.2.4 Accuracy of 6 50 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 The accuracy must not deteriorate by more than 6 100
accounted for in some scientific and engineering applications
Pa over a period of a year.
involving pressure dependent variables.
6.2.7 The hysteresis must be sufficiently small to ensure that
5.3 These methods provide a means of measuring atmo-
the difference in reading before a 5000-Pa pressure change and
spheric pressure with the accuracy and precision comparable to
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.
cistern and an index pointer projecting downward from the roof
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.
static pressure vent, such as that described by Gill (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
conditioning system, or both can be determined from pressure
Pa (b) extends below 80 000 Pa 6 80 Pa.
readings taken with a precision aneroid barometer inside and
6.1.2.2 For a marine application the error at a point must not
exceed 6 50 Pa.
6.1.3 Difference between errors over an interval of 10 000
Boldface numbers in parentheses refer to references at the end of these
Pa or less 6 30 Pa. methods.
D3631–99
outside the building on calm days when the ventilating and air 7.4 Work with mercury only in well-ventilated spaces,
conditioning system is in operation. The existence of pressure preferably under a fume hood or similar device. Use non-
errors due to the dynamic effects of wind on the building can permeable rubber gloves at all times and wash hands immedi-
often be diagnosed by careful observation of a fast response ately after any operation involving mercury. Exercise extreme
barometer in the building during periods of gusty winds. care to avoid spilling mercury. Minimize the effect of spills by
6.3.2 The significant pressure field near a building in wind working above a large shallow pan.
can extend to a height of 2.5 times the height of the building 7.5 Mercurial barometers should be installed only where
and to a horizontal distance up to 10 times the height of the there is adequate ventilation. The floor beneath a mercurial
building to the leeward. It may be impractical to locate a static barometer should be impermeable.
vent beyond this field but the following considerations must be 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;
8. Calibration and Standardization
6.3.2.4 To avoid blockages, a vertical run of connecting tube
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
secondary standard traceable to one of the primary standards at
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
has a minimum allowable internal diameter that is a function of
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
for pressure and temperature of the zero pressure altitude in the
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
connecting the static pressure head with the barometer must be
vertical distance of less than 0.5 m may be compared without
such that
correcting for height difference.
29 ¼ 8.3.1 Calibration of one or more barometers that do not
d . 7.21 3 10m LV! (1)
~
produce mutual interference with the standard or each other
where:
can be accomplished by simple comparison with traveling or
L = length of the tube, m,
fixed standards by methods described in Refs (1), (4), and (5).
V = volume of the air capacity of the pressure responsive
If the instruments used can cause mutual interference (for
instrument and any connected air chambers within the
system together with one half the volume of the
TABLE 2 Regional Standard Barometers
tubing, m , and
Region Location Category
d = inside diameter of the tubing, m.
When this calculation is made the minimum allowable inside I Pretoria, South Africa A
r
II Calcutta, India B
r
diameter will frequently be 5 mm or less. It is often more
III Rio de Janeiro, Brazil A
r
convenient to use tubing larger than this size, and use of such
Buenos Aires, Argentina B
r
larger tubing enhances the value of the static head and makes
Maracay, Venezuela B
r
IV Washington, DC, A
r
it applicable to a wider range of temperatures and pressures.
(Gaithersburg, Md.), USA
V Melbourne, Australia A
r
7. Safety Precautions
VI London, United Kingdom A
r
Leningrad, U.S.S.R. A
7.1 Warning: Mercury is a hazardous substance that can r
Paris, France A
r
cause illness and death. Inhalation of mercury vapor is a health
Hamburg, Federal Republic of A
r
hazard, even in small quantities. Prolonged exposure can
Germany
produce serious mental and physical impairment. Mercury can
A —A barometer that has been selected by regional agreement as a reference
r
also be absorbed through the skin, so avoid direct contact. The
...
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