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Significance and Use
5.3 This test method 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 method are valid only under the specified test conditions. Results would be affected by changes in 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.
5.6 The reliability of this test method 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.
1.1 This test method measures 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.
1.3 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.
2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.
E220 Test Method for Calibration of Thermocouples By Comparison Techniques
E230 Specification and Temperature-Electromotive Force (EMF) Tables for Standardized Thermocouples
E344 Terminology Relating to Thermometry and Hydrometry
E563 Practice for Preparation and Use of an Ice-Point Bath as a Reference Temperature
E1159 Specification for Thermocouple Materials, Platinum-Rhodium Alloys, and Platinum
ICS Number Code 17.200.20 (Temperature-measuring instruments)