1.1 本指南提供了一种方法，用于在规定的恒定高温下，使用双同时电动势指示器或使用单个电动势指示器，在交替测量测试电动势和参考电动势的情况下，测量以铂为基准的空气中贱金属热电偶材料的电动势稳定性。该测试持续数周。 1.2 校准的铂铑/铂热电偶用作参考标准，以确定测试温度。 1.3 热电偶的使用寿命取决于在给定温度下产生的电动势在所需时间间隔内的稳定性。该方法提供了单个热电偶稳定性的定量测量。通过结合正极（P）和负极（N）热电偶的结果，可以获得由P和N两种热电偶组成的热电偶的稳定性。 针对铂测量单个热电偶的电动势，铂可以是铂铑/铂参考热电偶的铂支腿，也可以是额外的铂参考。 注1: 一些热电偶在经历相对快速的氧化时可能会显示出轻微的电动势漂移。在这些情况下，热电偶的故障可能仅通过连接的热电偶之间的电阻大幅上升来表示，如在参考结处测量的那样。 注2: 见ASTM MNL 12表示空气中的推荐温度上限。 2. 注3: 本指南仅适用于最初的新热电偶。暴露在200°C以上温度下的基底金属热电偶变得热电不均匀，不均匀热电偶的稳定性测试将给出不明确的结果。 1.4 本标准并非旨在解决与其使用相关的所有安全问题（如有）。本标准的用户有责任在使用前制定适当的安全和健康实践，并确定监管限制的适用性。 ====意义和用途====== 5.1 该测试很重要，因为热电偶温度测量的准确性直接关系到热电偶的电动势稳定性。 5.2 本试验用于验证被测热电偶是否符合预期要求。 5.3 该测试有助于在相同条件下比较两个贱金属热电偶的电动势稳定性。测试和参考电动势可以同时或交替测量。 5.4 本试验确定的母材热电偶的相对稳定性仅在规定的试验条件下有效。结果将受到以下任何条件变化的影响:( 1. )沿热电偶长度的温度分布或梯度；( 2. )试样周围空气的丰度、速度和成分；( 3. )测试热电偶的热电不均匀性；( 4. )铂热电偶的稳定性。 5.5 本试验不涉及在一系列温度变化下测定基底金属热电偶的稳定性。 5.6 该测试的可靠性取决于参考铂热电偶的电动势稳定性。用于测试基座的相对电动势稳定性- 金属热电元件，应使用具有足够热电稳定性的铂参考元件，以确定基底金属热电元件电动势的任何重大变化。为了确定实验方法充分保护铂免受降解，应通过执行中所述的程序来验证该方法 附录X1 在实际测试之前。 5.7 测试结果不适用于给定测量结温度的温度分布随时间变化的应用。

1.1 This guide provides a method for measuring the emf stability of base-metal thermoelement materials in air referenced to platinum at specified constant elevated temperatures using dual, simultaneous, emf indicators, or using a single emf indicator, with the test and reference emf measured alternately. This test is conducted over a period of weeks. 1.2 A calibrated platinum-rhodium/platinum thermocouple is used as a reference standard to establish the test temperature. 1.3 The useful life of a thermocouple depends on the stability of the emf generated at given temperatures for a required time interval. This method provides a quantitative measure of the stability of individual thermoelements. By combining the results of the positive (P) and negative (N) thermoelements, the stability of a thermocouple comprised of both P and N thermoelements may be obtained. The emf of an individual thermoelement is measured against platinum, which may be the platinum leg of the platinum-rhodium/platinum reference thermocouple, or an additional platinum reference. Note 1: Some thermoelements may show insignificant emf drift while undergoing relatively rapid oxidation. In these cases, failure of the thermoelement may be indicated only by a large rise in the electrical resistance between joined thermoelements, as measured at the reference junctions. Note 2: See ASTM MNL 12 for recommended upper temperature limits in air. 2 Note 3: This guide is only applicable for initially new thermoelements. Base-metal thermoelements exposed to temperatures above 200°C become thermoelectrically inhomogeneous, and stability testing of inhomogeneous thermoelements will give ambiguous results. 1.4 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. ====== Significance And Use ====== 5.1 This test is important because the accuracy of a temperature measurement by a thermocouple is directly related to the emf stability of the thermoelements. 5.2 This test is used to verify that the tested thermoelements meet the intended requirements. 5.3 This test is useful in comparing the emf stability of two base metal thermoelements under the same conditions. The test and reference emf may be measured either simultaneously or alternately. 5.4 The relative stabilities of base metal thermoelements determined by this test are valid only under the specified test conditions. Results will be affected by changes in any of the following conditions: ( 1 ) temperature profile or gradient along the length of the thermoelements; ( 2 ) abundance, velocity and composition of the air surrounding the test pieces; ( 3 ) thermoelectric inhomogeneity of the test thermoelements; ( 4 ) stability of the platinum thermoelement. 5.5 The test does not address the determination of base metal thermoelement stabilities over a series of temperature changes. 5.6 The reliability of this test depends on the emf stability of the reference platinum thermoelement. For testing the relative emf stability of base-metal thermoelements, a reference element of platinum that has sufficient thermoelectric stability to determine any significant change in emf of base-metal thermoelements shall be used. To ascertain that the experimental method protects the platinum sufficiently from degradation, the method shall be validated by performing the procedure described in Appendix X1 prior to the actual test. 5.7 The test result does not apply to applications in which the temperature distribution, for a given measuring junction temperature, changes with time.