ASTM E220-19 PDF

Overview

ASTM E220-19 is the Standard Test Method for Calibration of Thermocouples By Comparison Techniques, developed by ASTM International. This standard provides rigorous instructions and requirements for calibrating unused thermocouples by comparing their electrical output (emf) with that of a reference thermometer across a temperature range of approximately −195 °C to 1700 °C (−320 °F to 3100 °F). Widely recognized in both industrial and laboratory settings, ASTM E220-19 ensures high accuracy and traceability in temperature measurements, supporting quality and compliance for commercial, military, and research applications.

Key Topics

• Purpose of Calibration: This standard outlines how to verify the emf–temperature characteristics of thermocouple materials before use, ensuring accurate temperature readings.
• Applicability: ASTM E220-19 is intended for unused thermocouples. Used thermocouples are excluded due to potential material inhomogeneity that can introduce significant measurement uncertainty.
• Calibration Principle: Unused thermocouples are calibrated by placing their measuring junction alongside a calibrated reference thermometer in an isothermal environment and comparing their output. Examples of reference thermometers include standard platinum resistance thermometers (SPRTs), liquid-in-glass thermometers, and reference thermocouples.
• Apparatus and Media: Common media for comparison include stirred liquid baths, tube furnaces, isothermal blocks, and fluidized powder baths-each chosen based on the temperature range and desired uncertainty.
• Reference Junctions: The standard emphasizes proper formation and compensation for reference junctions, such as using ice-point baths or electronic reference methods.
• Instrument Requirements: High-impedance electronic voltmeters are preferred for emf measurements to minimize loading errors. Provisions for noise reduction and thermal equilibrium are also specified.
• Uncertainty Management: The standard details practices for reducing and quantifying calibration uncertainties, including recommendations for insulation materials, connection techniques, and verification of reference thermometer performance.

Applications

• Reference Thermocouple Calibration: Use ASTM E220-19 to create highly accurate reference thermocouples, which can be used to calibrate other thermocouples or temperature sensors.
• Batch Testing: Ensure consistency and compliance of lots or batches of thermocouples before deployment in industrial equipment, process control, or research instrumentation.
• Specification Verification: Demonstrate conformance of thermocouple materials with recognized temperature–emf tables, such as those found in ASTM E230 or relevant customer or regulatory specifications.
• Quality Assurance: Support critical temperature measurement tasks in industries like aerospace, pharmaceuticals, energy, and laboratory research by providing traceable, standardized temperature calibration.

Related Standards

• ASTM E230 – Specification for Temperature-Electromotive Force Tables for Standardized Thermocouples: Lists standardized emf–temperature relationships for various thermocouple types.
• ASTM E563 – Practice for Ice-Point Bath Preparation: Offers methodology for maintaining reference junctions at precisely 0°C.
• ASTM E452 – Calibration of Refractory Metal Thermocouples: Addresses calibration procedures for high-temperature thermocouples.
• ASTM E1594 – Guide for Expression of Temperature: Details temperature scale conventions, such as ITS-90, as followed in E220-19.
• ASTM E1 & E77 – Pertains to the specification, inspection, and verification of liquid-in-glass thermometers often used in reference measurements.
• ASTM E2846 – Guide for Thermocouple Verification: Supplementary recommendations for ongoing performance verification of calibrated thermocouples.

Summary

For anyone involved in the manufacture, selection, or use of thermocouples for precise temperature measurement, ASTM E220-19 provides an internationally recognized, robust framework for calibration using comparison methodologies. Applying the recommendations in this standard enhances measurement reliability, supports regulatory and customer compliance, and ensures that temperature sensors perform within required tolerances across a broad range of industrial and scientific applications.