Astm D 4178 – 82 (Reapproved 1999) pdf free download

Standard Practice for
Calibrating Moisture Analyzers1

This standard is issued under the fixed designation D 4178; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of the 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

1.1 This practice describes a calibration technique based on
the preparation of standards of known water content. This
the technique is applicable to the production of standards between
20 and 2000 cm3
/m3 water.

1.2 The values stated in acceptable metric units are to be
regarded as the standard.

1.3 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.

2. Summary of Practice 2

2.1 The practice is based on the principle that ice has a
vapor pressure of 0.611 kPa at 0°C. Therefore, when a carrier
gas at a constant gage pressure of 207 kPa (30 psi) is passed
through a molecular sieve saturated with water and held at 0°C,
the total pressure is equal to 207 kPa plus 98 kPa (one
atmosphere) and the water concentration of the gas leaving the
molecular sieve is [0.611/(207 + 98)] 3 10 6 ppm or 2000 ppm
volume water, regardless of flow.

2.1.1 A carrier gas at a constant gage pressure of 207 kPa is
passed through a molecular sieve drier and then routed over a
molecular sieve support saturated with water and equilibrated
at 0°C.

2.1.2 By blending different volumes of the wet carrier gas
with a dried carrier gas, gas standards of known water concentration can be prepared.

2.2 The moisture analyzer to be calibrated is then connected
to the source of the gas standard of known water concentration.

3. Significance and Use

3.1 This practice is intended to provide a method to calibrate moisture analyzers used on-stream or in the laboratory.

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