Overview
EN ISO 376:2011 (ISO 376:2011) specifies a standardized method for the calibration of force‑proving instruments used to perform the static verification of uniaxial testing machines (for example, tension and compression testing machines). The standard covers instruments that determine force by measuring the elastic deformation of a loaded member (or a quantity proportional to that deformation) and defines procedures for calibration, classification and use.
Key topics and requirements
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Scope and principle
- Applies to force‑proving instruments where force is inferred from elastic deformation.
- Calibration is performed by applying known forces and recording the indicator output as an integral part of the assembly.
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Instrument identification and characteristics
- Unique identification of all elements (manufacturer, model, serial number) and indication of maximum working force for the transducer.
- Loading fittings and transducer design must ensure axial application of force in tension/compression.
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Measurement system and indicators
- Deflection measurement may be mechanical, electrical, optical, etc.; the method affects allowable interpolation and classification.
- Rules for replacing indicators without full recalibration (traceable electrical calibration, compatible excitation, and limited additional uncertainty).
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Calibration procedures and tests
- Options for calibration with reversible (increasing/decreasing) forces or with increasing forces only - influencing whether hysteresis or creep tests are required.
- Preliminary checks such as overload tests, verification of axial loading, and (optionally) variable voltage tests for electrically excited instruments.
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Performance metrics and errors
- Definitions and symbols for repeatability, reproducibility, interpolation error, zero error, reversibility, creep and resolution (see Clause 4 and Table 1).
- Annex C provides guidance on measurement uncertainty of calibration and subsequent use.
Applications and who uses this standard
- Calibration and testing laboratories performing verification of uniaxial testing machines.
- Manufacturers of force transducers, force‑proving instruments and calibration equipment.
- Quality, test and R&D engineers in metallurgical, aerospace, automotive and materials testing sectors.
- Accreditation bodies and laboratories applying ISO/IEC 17025 for traceable calibration services.
- Maintenance teams ensuring test-machine verification and compliance with traceability and uncertainty requirements.
Related standards and documents
- Normative reference: ISO/IEC 17025 (competence of testing and calibration laboratories).
- EN ISO 376:2011 supersedes earlier EN ISO 376:2004 editions; consult national/adopted versions for legal/administrative status.
EN ISO 376:2011 is essential for organizations that require reliable, traceable force calibration for uniaxial testing, ensuring consistent verification of tensile/compression testing machines and well‑documented measurement uncertainty.