ASTM E220-2019 pdf free download

ASTM E220-2019 pdf free download.Standard Test Method for Calibration of Thermocouples By Comparison Techniques
1. Scope
1.1 This test method describes the principles, apparatus, and procedure for calibrating thermocouples by comparison with a reference thermometer. Calibrations are covered over tempera- ture ranges appropriate to the individual types of thermo- couples within an overall range from approximately −195 °C to 1700 °C (−320 °F to 3100 °F). 1.2 In general, this test method is applicable to unused thermocouples. This test method does not apply to used thermocouples due to their potential material inhomogeneity— the effects of which cannot be identified or quantified by standard calibration techniques. Thermocouples with large- diameter thermoelements and sheathed thermocouples may require special care to control thermal conduction losses. 1.3 In this test method, all values of temperature are based on the International Temperature Scale of 1990. See Guide E1594. 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 appro- priate safety, health, and environmental practices and deter- mine the applicability ofregulatory limitations prior to use. 1.5 This international standard was developed in accor- dance with internationally recognized principles on standard- ization established in the Decision on Principles for the Development of International Standards, Guides and Recom- mendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
3. Terminology
3.1 Definitions—The definitions given in Terminology E344 shall apply to this test method. 3.2 Definitions ofTerms Specific to This Standard: 3.2.1 check standard, n—a measurement instrument or stan- dard whose repeated results of measurement are used to determine the repeatability of a calibration process and to verify that the results of a calibration processes are statistically consistent with past results. 3.2.2 isothermal block, n—a piece of solid material of high thermal conductivity used to promote thermal equilibrium between two or more thermometers. 3.2.3 reference junction compensation, n—the adjustment of the indication of a thermocouple such that the adjusted indication is equivalent to the emf or temperature that the thermocouple would indicate if the reference junctions were maintained at 0 °C. 3.2.3.1 Discussion—In most cases, the thermocouple indi- cation is adjusted by measuring the temperature of a terminal block where the thermocouple is connected, and then adding to the thermocouple emfan additional emfequal to the emfofthe thermocouple reference function evaluated at the temperature of the terminal block. Because the emf-temperature relation- ship ofany actual thermocouple differs slightly from that ofthe reference function, reference junction compensation typically introduces higher uncertainties compared to the use of a well prepared ice bath. 3.2.4 reference junction compensator, n—a device that implements reference junction compensation. 3.2.5 reference thermometer, n—thermometer that estab- lishes the value of temperature in a given system containing additional temperature sensors. 3.2.5.1 Discussion—In a calibration system the reference thermometer is a calibrated thermometer capable of indicating values of temperature with known uncertainty. The reference thermometer provides the standard temperature for the system at the time of test. 3.2.6 thermocouple type, n—a standardized thermoelectric class of thermoelement materials that, used as a pair, have a normal relationship between relative Seebeck emf and tem- perature. 3.2.6.1 Discussion—For common, commercially available thermocouples, a thermocouple type is identified by a letter designation (types B, C, E, J, K, N, R, S, and T). The letter designation scheme is given in Guide E2846. The tables in E1751 give temperature-EMF relationships for a number of additional thermocouple compositions that are not identified by a letter designation.