Permeameters & Gaussmeters - Precision Tools for Material Properties & Field Mapping

Subject: Beyond Moment: Measuring Intrinsic Properties with Permeameters & Gaussmeters

While Helmholtz coils measure bulk moment, understanding a permanent magnet material's intrinsic properties (like Br, HcB, HcJ, (BH)max) requires more sophisticated tools: Permeameters (or Hysteresisgraph Systems). For detailed surface field mapping, Gaussmeters (Teslameters) with Hall probes are indispensable.

1. Function: These systems create a closed magnetic circuit. The magnet sample (often a cube or cylinder) is placed between heavy ferromagnetic pole pieces within an electromagnet. A sensitive fluxmeter measures the magnetic flux (B) through the sample, while the applied field (H) is measured, typically using a calibrated Hall sensor or search coil near the sample.

2. Output: They trace the full B-H or M-H demagnetization curve under controlled conditions (often per standards like IEC 60404-5). This curve directly yields the critical parameters:

• Remanence (Br): Flux density at zero applied field.
• Coercivity (HcB): Field needed to reduce B to zero.
• Intrinsic Coercivity (HcJ): Field needed to reduce magnetization M to zero (critical for stability).
• Maximum Energy Product ((BH)max): The peak value of B*H on the curve.

3. Use Case: Essential for R&D, material development, advanced quality control, and verifying grade specifications (e.g., N52). Requires careful sample preparation and standardized procedures.

1. Function: Measure the local magnetic flux density (B) at a specific point near the magnet surface. A handheld probe contains a Hall sensor that outputs a voltage proportional to the field component perpendicular to its active area.

2. Key Applications:

• Surface Field Mapping: Scanning a probe over a magnet surface reveals field strength variations, crucial for assessing uniformity, detecting flaws, or designing assemblies.
• Air Gap Field Measurement: Measuring field strength in gaps within magnetic circuits.
• Quality Checks: Verifying field strength at specific points (e.g., pole centers).
• Complementing Permeameters: Often used within permeameter systems to measure H-field.

3. Probe Types: Axial (measures field along probe axis) and Transverse (measures field perpendicular to axis). Choice depends on magnet geometry and measurement needs. Calibration is paramount!

If you need deep material characterization (Br, HcJ, (BH)max) or detailed spatial field information for design or advanced QA, permeameters and gaussmeters provide the necessary precision and flexibility. They are the gold standard for intrinsic property measurement.