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DRAFT⚠OIML SMART pilot programme · internal use only · all documents and specifications are drafts and may change without notice
OIML SMART

OIML R 60: Metrological regulation for load cells

The pilot SMART Recommendation. Load cells are the most widely deployed measuring instruments in legal metrology, used in every nonautomatic weighing instrument from retail scales to vehicle weighbridges.

Scope

OIML R 60:2021 specifies the metrological and technical requirements, test procedures, and test report format for load cells, the force transducers at the heart of every nonautomatic weighing instrument.

The Recommendation covers load cells used in instruments subject to legal metrology control, including:

  • Single-cell and multiple-cell configurations.
  • Analog and digital output.
  • Accuracy classes: A, B, C, D.
  • Maximum number of verification scale intervals (nLC) per class.

What’s modelled

The SMART decomposition of R 60 captures the full Recommendation end-to-end:

Layer Count Notes
Requirements 42 Tiered, threshold, and qualitative criteria
Conformance tests 18 Including measurement error, repeatability, creep, hysteresis, temperature effects
Forms 12 With embedded MPE lookups and pass/fail logic
Terminology ~80 Cross-referenced across the Recommendation
Ontology entities ~30 In the load-cell domain ontology

Headline tests

  • Measurement error (R 60 §3.4.1), verifies that errors at increasing and decreasing loads stay within the maximum permissible error (MPE) for the instrument’s accuracy class and load range.
  • Repeatability (R 60 §3.4.2), verifies that repeated loadings at the same point produce readings within a tight tolerance.
  • Creep (R 60 §3.4.3), verifies the load cell reading is stable over time under constant load.
  • Temperature effects (R 60 §3.4.4), verifies the cell performs within tolerance across its rated temperature range.

Each test maps to one or more requirements via the cross-reference graph; the SMART evaluation pipeline aggregates the per-test verdicts into the overall type evaluation.

MPE table

The maximum permissible error varies by accuracy class and load range. In the SMART model this is encoded as a Table primitive, declared once in standard.yaml and referenced by every form that needs an MPE value:

table: r60_mpe_table
kind: range
inputs:
  - name: accuracy_class
    type: enum
    values: [A, B, C, D]
  - name: load
    type: numeric
    unit: Max   # fraction of maximum capacity
output:
  name: mpe
  unit: e   # verification scale interval
ranges:
  - when: { accuracy_class: A, load: [0, 50000] }
    value: 0.5
  - when: { accuracy_class: A, load: [50000, 200000] }
    value: 1.0
  # ...

Explore the model

Certification path

To certify a load cell under OIML-CS:

  1. Manufacturer submits an application.
  2. Issuing Authority commissions a test laboratory.
  3. TL performs the 18 conformance tests, populating the SMART forms.
  4. IA consolidates results into an Evaluation Report.
  5. If conforming, IA issues an OIML Certificate bearing the OIML-CS logo.

The certificate number follows PD-05 Annex B format, e.g. R60-A-DE1-2024-001.