ASTM E220-25 PDF

Full title and description

ASTM E220-25 — Standard Test Method for Calibration of Thermocouples by Comparison Techniques. This standard describes the principles, apparatus, and procedures for calibrating thermocouples by comparison with a reference thermometer across temperature ranges appropriate to individual thermocouple types, and provides guidance for verification of thermocouple material conformance to specified temperature tolerances.

Abstract

ASTM E220-25 defines a comparison calibration method in which a test thermocouple is compared to a reference thermometer or reference thermocouple under controlled conditions. The method covers an overall temperature range from about −196 °C to 1700 °C (approximately −321 °F to 3092 °F), specifies recommended apparatus and procedures, addresses uncertainty considerations, and notes applicability limits (generally for unused thermocouples). The standard references the International Temperature Scale of 1990 (ITS-90) as the temperature basis.

General information

• Status: Active.
• Publication date: 01 May 2025 (published May 2025).
• Publisher: ASTM International.
• ICS / categories: Temperature-measuring instruments — ICS 17.200.20 (temperature-measuring instruments) / Sensory evaluation; temperature measurement category.
• Edition / version: E220-25 (2025 revision).
• Number of pages: 15 pages.

Scope

This test method describes the principles, apparatus, and procedure for calibrating thermocouples by comparison with a reference thermometer. Calibrations are intended to cover temperature ranges appropriate to individual thermocouple types within an overall range from approximately −196 °C to 1700 °C (−321 °F to 3092 °F). The method is generally applicable to unused thermocouples; it does not apply to used thermocouples where material inhomogeneity may affect results. Temperatures in the standard are referenced to ITS-90.

Key topics and requirements

• Comparison calibration technique: procedures for comparing a test thermocouple to a calibrated reference thermometer or thermocouple.
• Apparatus and environmental controls: recommended baths, furnaces, ice-point or fixed-point arrangements, immersion depths, and thermal stability requirements.
• Calibration range and limits: guidance for ranges up to ~1700 °C and low-temperature coverage to about −196 °C, and special considerations for large-diameter or sheathed thermocouples.
• Uncertainty and measurement reporting: considerations for estimating and reporting calibration uncertainty and repeatability.
• Applicability and exclusions: suitability for unused thermocouples; limitations for used or inhomogeneous elements.
• Reference scales and supporting documents: use of ITS-90 and cross-reference to related ASTM specifications (e.g., E230) and guides (e.g., Guide E1594) where applicable.

Typical use and users

Calibration laboratories, instrument manufacturers, research laboratories, aerospace and defense facilities, industrial process measurement groups, and quality/inspection departments use ASTM E220-25 to verify thermocouple performance, establish calibration certificates, and confirm material conformance to temperature-tolerance specifications. It is commonly used when reference-grade thermometry and documented uncertainty budgets are required.

Related standards

Commonly referenced documents include ASTM E230 (Tables of Thermoelectric EMF of Standard Thermocouples), ASTM Guide E1594 (use of ITS-90 in temperature measurements), and laboratory accreditation requirements such as ISO/IEC 17025 for calibration labs. The E220-25 revision replaces and updates earlier E220 editions.

Keywords

thermocouple, calibration, comparison technique, thermoelement, reference thermometer, ITS-90, uncertainty, temperature measurement, E220-25.

FAQ

Q: What is this standard?

A: ASTM E220-25 is a test method that specifies how to calibrate thermocouples by comparing them with a reference thermometer or calibrated reference thermocouple, including recommended apparatus and procedures.

Q: What does it cover?

A: It covers comparison calibration techniques over an overall range from approximately −196 °C to 1700 °C, requirements for apparatus and control, guidance on uncertainty, and applicability notes (generally for unused thermocouples).

Q: Who typically uses it?

A: Calibration laboratories, manufacturers of thermocouples and temperature instrumentation, research establishments, process control engineers, and organizations needing traceable thermocouple calibrations and documented uncertainty.

Q: Is it current or superseded?

A: Current — the active revision is ASTM E220-25, published 01 May 2025 (the 2025 revision supersedes earlier editions).

Q: Is it part of a series?

A: E220 is part of ASTM’s temperature-measurement standards and is commonly used alongside related ASTM documents such as E230 and Guide E1594; it is maintained by Subcommittee E20.11.

Q: What are the key keywords?

A: Thermocouple calibration, comparison technique, thermoelement, reference thermometer, ITS-90, measurement uncertainty, temperature measurement.