ASTM A772/A772M-00(2022) PDF

Overview

ASTM A772/A772M-00(2022), "Standard Test Method for AC Magnetic Permeability of Materials Using Sinusoidal Current," establishes procedures for measuring the impedance permeability of ferromagnetic materials. Released by ASTM International, this standard is specifically designed to evaluate materials subjected to sinusoidal current using test specimens such as laminated toroidal cores, tape-wound toroidal cores, and link-type laminated cores. The method is applicable for ferromagnetic strips with thicknesses less than or equal to 0.025 in. [0.635 mm] and is intended as a means to determine key magnetic properties for quality control, research, performance evaluation, and specification compliance.

Key Topics

• Impedance Permeability Measurement: The standard focuses on determining impedance permeability (μz), defined as the ratio of the peak value of magnetic flux density (Bmax) to the assumed peak magnetic field strength (Hz) under sinusoidal current excitation.
• Test Frequency Range: Suitable for measurements at power frequencies (50 Hz to 60 Hz), with applicability extending up to 1 MHz using appropriate test equipment and procedures.
• Specimen Types: Utilizes laminated toroidal, tape-wound toroidal, and link-type laminated cores, specifically those with uniform cross sections and closed flux paths.
• Test Preparation: Encompasses procedures for specimen preparation, demagnetization, and connecting primary and secondary windings to minimize measurement inaccuracies.
• Calculation Methods: Provides equations and procedures for computing mean magnetic path length, cross-sectional area, magnetic field strength, and permeability in both customary and SI units.
• Measurement Limitations: Emphasizes the requirement for a high total series resistance to primary coil impedance ratio (≥10) and the importance of maintaining pure sinusoidal current for accurate results.
• Safety and Compliance: Stresses the user’s responsibility to institute proper safety, health, and environmental practices, and addresses compliance with international standardization principles.

Applications

• Material Design and Research: Used to characterize the magnetic properties of ferromagnetic material strips during new material development and applied research.
• Specification Acceptance: Serves as a basis for acceptance testing of magnetic materials against industry or customer specifications.
• Quality Control: Facilitates routine verification of material batches to ensure compliance with required magnetic performance thresholds.
• Service Evaluation: Assesses the suitability of materials for applications such as electrical transformers, inductors, and other components where magnetic permeability is critical.
• Standardized Reporting: Ensures comparability and reproducibility of results through standardized test setups and calculation protocols.

Related Standards

• ASTM A34/A34M: Practice for Sampling and Procurement Testing of Magnetic Materials, which guides sample preparation and procurement for magnetic testing activities.
• ASTM A340: Terminology of Symbols and Definitions Relating to Magnetic Testing, a reference for terminology and symbol usage across related standards.
• International Principles: This standard is developed in alignment with principles established by the World Trade Organization Technical Barriers to Trade (TBT) Committee, supporting harmonization and international acceptance.

Keywords: ASTM A772, AC magnetic permeability, sinusoidal current test, impedance permeability, ferromagnetic materials, laminated toroidal cores, magnetic properties testing, quality control, SI and inch-pound units, standard test method.

For more information or to obtain the full standard, visit the ASTM website.