ASTM & IEC Thermocouple Standards
Complete reference for all ASTM and IEC standards applicable to thermocouples — EMF tables, calibration methods, tolerance classes, verification, and conductor specifications.
Applicable ASTM Standards
ASTM E230 — Standard Specification and Temperature-EMF Tables for Standardized Thermocouples
The primary US standard for base-metal thermocouples. Defines: EMF-temperature reference functions (polynomial coefficients per ITS-90) for Types J, K, T, E, and N; Standard and Special limits of error; alloy composition requirements for each conductor alloy; ANSI color code designations; and extension wire designations (JX, KX, TX, EX, NX). All products conforming to this standard must meet the EMF-temperature tables within the specified tolerance class limits.
| Type | Std Tolerance (0°C+) | Special Tolerance | Sub-zero Tolerance |
|---|---|---|---|
| J | ±2.2°C or ±0.75% | ±1.1°C or ±0.4% | ±2.2°C or ±2.0% |
| K | ±2.2°C or ±0.75% | ±1.1°C or ±0.4% | ±2.2°C or ±2.0% |
| T | ±1.0°C or ±0.75% | ±0.5°C or ±0.4% | ±1.0°C or ±1.5% |
| E | ±1.7°C or ±0.5% | ±1.0°C or ±0.4% | ±1.7°C or ±1.0% |
| N | ±2.2°C or ±0.75% | ±1.1°C or ±0.4% | ±2.2°C or ±2.0% |
ASTM E220 — Standard Method for Calibration of Thermocouples by Comparison Techniques
Defines the procedure for calibrating thermocouples by comparison with a NIST-traceable reference standard (Type S thermocouple, SPRT, or other calibrated reference) in a stable thermal environment. Covers: furnace and bath requirements (temperature uniformity, stability), ice point reference junction requirements, nanovoltmeter accuracy, and documentation. Calibrations performed per ASTM E220 provide the foundation for NIST-traceable calibration certificates.
ASTM E1751 — Standard Temperature-EMF Tables for Noble Metal Thermocouples
Defines EMF-temperature reference functions and limits of error for platinum-rhodium noble metal thermocouples. Covers Types R (Pt-13%Rh/Pt), S (Pt-10%Rh/Pt), and B (Pt-30%Rh/Pt-6%Rh). Standard tolerance for R and S: ±1.5°C or ±0.25%. Special tolerance: ±0.6°C or ±0.1%. Type B tolerance is percentage-only above 600°C. Reference functions per ITS-90.
ASTM E696 — Standard Specification for Tungsten-Rhenium Alloy Thermocouples
Covers the W-5%Re / W-26%Re (Type C) thermocouple for extreme high-temperature service to +2315°C. Specifies conductor alloy composition, EMF-temperature tables (0 to 2315°C), and limits of error: Standard ±4.5°C or ±1.0%; Special ±2.3°C or ±0.5%. Critical requirement: Type C must only be used in vacuum, hydrogen, or inert (Ar/He) atmospheres. Oxidizing atmospheres cause catastrophic tungsten oxidation.
ASTM E2846 — Guide for Thermocouple Verification
Provides guidance for verifying that thermocouples in service continue to conform to their original EMF-temperature tables within tolerance class limits. Distinguishes between calibration (absolute measurement against traceable reference) and verification (confirming continued conformance). Describes in-situ verification methods, documentation requirements, and acceptance criteria. Required reading for AMS 2750, ISO 9001, and FDA-regulated applications.
IEC 60584 — International Standards
60584-1
IEC 60584-1 — EMF Reference Tables
International equivalent of ASTM E230 and E1751. Defines EMF-temperature reference functions for Types B, E, J, K, N, R, S, and T. Reference functions are harmonized with ASTM and NIST — thermocouples conforming to ASTM E230 will also conform to IEC 60584-1 for base-metal types. Minor differences exist in the polynomial coefficients at extreme temperature ranges.
60584-2
IEC 60584-2 — Tolerances
Defines tolerance classes for all standardized thermocouple types. IEC Class 1 approximates ASTM Special tolerance; IEC Class 2 approximates ASTM Standard tolerance. Class 3 (extended sub-zero) applies to Types K, N, T, and E at temperatures below −200°C. Used in European and international specifications where ASTM designation is not specified.
60584-3
IEC 60584-3 — Extension and Compensating Cables
Specifies requirements for thermocouple extension and compensating cables — alloy compositions, tolerances, insulation temperature ratings, and color codes. IEC color codes differ from ANSI (US) codes. The negative conductor is always White in IEC; always Red in ANSI. Verify wire designation and color code standard before installation to avoid errors.
The definitive source for ITS-90 based EMF-temperature reference functions for all standardized thermocouple types. Provides complete polynomial coefficients, inverse functions (EMF to temperature), and full tabulated values at 1°C intervals. Available from NIST at no charge. All ASTM E230 and IEC 60584-1 tables are derived from NIST MN 175.