Overview
ISO 376:2011 - Metallic materials - Calibration of force‑proving instruments used for the verification of uniaxial testing machines - defines a standardized method to calibrate and classify force‑proving instruments (force transducers plus indicator) used to statically verify uniaxial testing machines (tension/compression). The standard applies to instruments where force is determined by measuring elastic deformation or a directly proportional quantity and includes procedures to establish measurement traceability, repeatability and uncertainty.
Key technical topics and requirements
- Scope and applicability: Calibration method for force‑proving instruments that measure force via elastic deformation; intended for static verification of uniaxial testing machines.
- Calibration principle: Apply precisely known forces and record indicator readings; the indicator is treated as an integral part of the instrument.
- Calibration modes:
- Reversible (incremental/decremental) - calibration with increasing and decreasing forces to determine hysteresis (no creep test needed).
- Incremental‑only - calibration with increasing forces only; requires a creep test (readings at 30 s and 300 s) instead of hysteresis measurement.
- Preloading and loading procedure: Preload to maximum force three times; perform multiple series of calibration forces (including rotation of the transducer at prescribed angles) and ensure at least eight forces for reliable interpolation of the calibration curve.
- Indicator resolution and replacement: Minimum resolution rules for analogue/digital indicators; replacement indicators must have traceable calibration and compatible excitation/uncertainty so they do not materially affect the overall system uncertainty.
- Minimum force and classification: Minimum calibration forces depend on instrument class (e.g., classes 00, 0.5, 1, 2) and a fraction of the transducer capacity; classification procedure included.
- Environmental and procedural controls: Temperature stability (18–28 °C, ±1 °C), uniform loading intervals, strain gauge warm‑up (≥30 min), and dismantling checks.
- Ancillary documentation and annexes: Annexes provide example loading fittings/dimensions (A), additional procedures (B), and a new Annex C addressing measurement uncertainty of calibration and subsequent use. Normative reference: ISO/IEC 17025.
Practical applications and users
Who uses ISO 376:2011:
- Calibration and metrology laboratories performing force transducer calibrations
- Material testing laboratories verifying uniaxial tensile/compression machines
- Manufacturers of force transducers and testing machines seeking traceable calibration procedures
- Quality managers and compliance officers ensuring test system accuracy and conformity
Practical benefits:
- Ensures accurate, traceable force measurements and reliable machine verification
- Provides a consistent basis for reporting measurement uncertainty and classification
- Supports compliance with laboratory accreditation requirements (e.g., ISO/IEC 17025)
Related standards
- ISO/IEC 17025 - General requirements for the competence of testing and calibration laboratories (normative reference in ISO 376:2011)
- Additional ISO technical committee guidance on mechanical testing (ISO/TC 164) may be relevant for broader test program compliance.
Keywords: ISO 376:2011, calibration, force‑proving instruments, uniaxial testing machines, force transducer, calibration procedure, measurement uncertainty, hysteresis, creep test, ISO/IEC 17025.
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