ASTM E1750-02
(Guide)Standard Guide for Use of Water Triple Point Cells
Standard Guide for Use of Water Triple Point Cells
SIGNIFICANCE AND USE
This guide describes a procedure for placing a water triple-point cell in service and for using it as a reference temperature in thermometer calibration.
The reference temperature attained is that of a fundamental state of pure water, the equilibrium between coexisting solid, liquid, and vapor phases.
The cell is subject to qualification but not to calibration. The cell may be qualified as capable of representing the fundamental state (see 4.2) by comparison with a bank of similar qualified cells of known history, and it may be so qualified and the qualification documented by its manufacturer.
The temperature to be attributed to a qualified water triple-point cell is exactly 273.16 K on the ITS-90.
Continued accuracy of a qualified cell depends upon sustained physical integrity. This may be verified by techniques described in Section 6.
The commercially available triple point of water cells described in this standard are capable of achieving an expanded uncertainty (k=2) of between ±0.1 mK and ±0.05 mK, depending upon the method of preparation. Specified measurement procedures shall be followed to achieve these levels of uncertainty.
SCOPE
1.1 This guide covers the nature of two commercial water triple-point cells (types A and B, see Fig. 1) and provides a method for preparing the cell to realize the water triple-point and calibrate thermometers. Tests for assuring the integrity of a qualified cell and of cells yet to be qualified are given. Precautions for handling the cell to avoid breakage are also described.
1.2 The effect of hydrostatic pressure on the temperature of a water triple-point cell is discussed.
1.3 Procedures for adjusting the observed SPRT resistance readings for the effects of self-heating and hydrostatic pressure are described in Appendix X1 and Appendix X2.
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.
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Designation: E 1750 – 02
Standard Guide for
1
Use of Water Triple Point Cells
This standard is issued under the fixed designation E1750; 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 (e) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
The triple point of water is an important thermometric fixed point common to the definition of two
temperature scales of science and technology, the KelvinThermodynamicTemperature Scale (KTTS)
and the International Temperature Scale of 1990 (ITS-90). The ITS-90 was designed to be as close to
the KTTS as the experimental data available at the time of the adoption of the ITS-90 would permit.
The temperatures (T) on the KTTS are defined by assigning the value 273.16 K to the triple point of
water, thus defining the thermodynamic unit of temperature, kelvin (K), as 1/273.16 of the
2
thermodynamic temperature of the triple point of water (1, 2). The triple point of water, one of the
fixed points used to define the ITS-90, is the temperature to which the resistance ratios W(T)=R(T)/
R(273.16 K) of the standard platinum resistance thermometer (SPRT) calibrations are referred.
The triple points of various materials (where three distinct phases, for example, their solid, liquid,
andvaporphases,coexistinastateofthermalequilibrium)havefixedpressuresandtemperaturesand
are highly reproducible. Of the ITS-90 fixed points, six are triple points. The water triple point is one
of the most accurately realizable of the defining fixed points of the ITS-90; under the best of
conditions, it can be realized with an expanded uncertainty (k=2) of less than 60.00005 K. In
comparison, it is difficult to prepare and use an ice bath with an expanded uncertainty (k=2) of less
than 60.002 K (3).
The triple points of various materials (where three distinct phases, for example, their solid, liquid,
andvaporphases,coexistinastateofthermalequilibrium)havefixedpressuresandtemperaturesand
are highly reproducible. Of the ITS-90 fixed points, six are triple points. The water triple point is one
of the most accurately realizable of the defining fixed points of the ITS-90; under the best of
conditions, it can be realized with an expanded uncertainty (k=2) of less than 60.00005 K. In
comparison, it is difficult to prepare and use an ice bath with an expanded uncertainty (k=2) of less
than 60.002 K (3).
1. Scope 1.2 The effect of hydrostatic pressure on the temperature of
a water triple-point cell is discussed.
1.1 This guide covers the nature of two commercial water
1.3 Procedures for adjusting the observed SPRT resistance
triple-point cells (types A and B, see Fig. 1) and provides a
readings for the effects of self-heating and hydrostatic pressure
method for preparing the cell to realize the water triple-point
are described in Appendix X1 and Appendix X2.
and calibrate thermometers. Tests for assuring the integrity of
1.4 This standard does not purport to address all of the
a qualified cell and of cells yet to be qualified are given.
safety concerns, if any, associated with its use. It is the
Precautions for handling the cell to avoid breakage are also
responsibility of the user of this standard to establish appro-
described.
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use.
1
This guide is under the jurisdiction ofASTM Committee E20 on Temperature
Measurement and is the direct responsibility of Subcommittee E20.07 on Funda-
2. Referenced Documents
mentals in Thermometry.
2.1 ASTM Standards:
Current edition approved May 10, 2002. Published June 2002. Originally
published as E1750–95.
2
Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
this standard.
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E1750–02
3.2.1 inner melt, n—a thin continuous layer of water be-
tween the thermometer well and the ice mantle of a water
triple-point cell.
3.2.2 reference temperature, n—the temperature of a phase
equilibriumstateofapuresubstanceataspecifiedpressure,for
example, the assigned temperature of a fixed point.
3.2.2.1 Discussion—at an equilibrium state of three phases
of a substance, that is, at the triple point, both the temperature
and pressure are fixed.
4. Significance and Use
4.1 This guide describes a procedure for placing a water
triple-point cell in service and for using it as a reference
temperature in thermometer calibration.
4.2 The reference temperature attained is that of a funda-
mental state of pure water, the equilibrium between coexisting
solid, liquid, and v
...
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