【国外标准】 Standard Practice for Preparation and Use of an Ice-Point Bath as a Reference Temperature

5.1 This practice is adequate for use with other ASTM standards that specify the ice point as a reference. It is also intended to be adequate for most other ice-point reference purposes.5.2 The ice point is a common practical industrial reference point of thermometry. The ice point is relatively simple to realize and provides a readily available natural fixed-point reference temperature.5.3 Use in Resistance Thermometry: 5.3.1 The ice point was a defining fixed point on practical temperature scales prior to 1960.5.3.2 The ITS-90 defines W(T90) = R(T90)/R(273.16 K), the measured resistance ratio of a Standard Platinum Resistance Thermometer (SPRT), in reference to the water triple point, not the ice point (1).3 In many instances, where the water triple point is not available, or when the accuracy obtainable with the water triple point is not required, reference to a properly established and maintained ice-point reference is used. For industrial-quality resistance thermometers, the resistance value is determined for 0 °C, and an uncertainty that is appropriate for the quality of the ice-point realization is assigned.5.4 Use in Thermoelectric Thermometry: 5.4.1 In thermoelectric thermometry, the ice point is ordinarily used as the reference temperature (2).5.4.2 Adequate thermoelectric reference requires that thermocouple junctions be well-coupled thermally to the bath, electrically isolated from each other and from the bath, and adequately immersed to avoid perturbing the reference-junction temperatures by radiation and longitudinal conduction of heat along the thermoelements (3 and 4).5.5 Use in Liquid-in-Glass Thermometry: 5.5.1 In liquid-in-glass thermometry, the ice point is ordinarily used as the reference temperature (5).5.5.2 The periodic recalibration of a liquid-in-glass thermometer at the ice point provides a reliable indication of the effect of gradual relaxation of residual mechanical strains in the glass that have a significant effect on the volume of the bulb (5).1.1 This practice covers a method of preparing, maintaining, and using a temperature reference bath of a mixture of shaved ice and water, saturated with air at a pressure of 101 325 Pa (1 atm).1.2 An industrial practice for relating values referenced to the ice point and to the water triple point on the ITS-90 is included.1.3 Methods to promote uniformity of bath temperature by mechanical stirring or agitation are not described in detail.1.4 Methods of approximating the ice point, as by thermostatically-controlled refrigeration, are not covered by this practice.1.5 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.6 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.