⚖️ Balance Calibration and Verification

Metrology PN-EN 45501

Overview

STATUS (as of 06.11.2026). PN-EN 45501:2015-05 (Polish version published on 05.12.2016) implements EN 45501:2015 and replaced PN-EN 45501:1999; it has the national correction Ap1:2018-03 (A.4.6.1 — weighing accuracy test with different tare values, instead of “at least two”). The standard specifies metrological and technical requirements for non-automatic weighing instruments and standardised test procedures; EN 45501:2015 was adapted by a joint CEN and CENELEC working group from the international recommendation OIML R 76-1:2006, following a standardisation request of the European Commission related to Directive 2009/23/EC (repealed with effect from 20.04.2016 by Directive 2014/31/EU), and the EURAMET cg-18 guideline cites both interchangeably. Title of the recommendation: “Non-automatic weighing instruments — Part 1: Metrological and technical requirements — Tests”. Both set metrological and technical requirements and tests of instruments — for type approval and conformity assessment — not a calibration procedure. The calibration of weighing instruments is described in the EURAMET Calibration Guide No. 18 (cg-18, version 4.0, 2015), which uses the terms of OIML R 76 / EN 45501; the calibration description below follows it.

CLASSES AND MAXIMUM PERMISSIBLE ERRORS (OIML R 76-1, 3.1–3.5). Accuracy classes: I — special, II — high, III — medium, IIII — ordinary. The class determines the verification scale interval e, the number of intervals n = Max/e and the minimum capacity Min (e.g. class I: e ≥ 0.001 g, n at least 50 000, Min = 100 e). Maximum permissible errors on initial verification are ± 0.5 e, ± 1.0 e or ± 1.5 e depending on the load (Table 6), and in service — twice these values. An instrument without marked working temperature limits shall keep its metrological properties within −10 °C … +40 °C.

CALIBRATION (EURAMET cg-18, clauses 4–5). Calibration consists of applying test loads under specified conditions, determining the error of indication (E = I − m_ref) and evaluating the uncertainty. It normally covers the full weighing range from zero to Max and is performed at the place of use — moving the instrument after calibration may invalidate it. Before calibration the instrument is energised for an appropriate period, levelled and loaded at least once to approximately the largest test load; an instrument which the user regularly adjusts before use is adjusted before calibration. Tests: repeatability — the same load at least 5 times (at least 3 times for 100 kg and more), commonly 0.5 Max–Max; errors of indication — at least 5 loads distributed over the range (e.g. zero or Min, 0.25 Max, 0.5 Max, 0.75 Max, Max); eccentricity — a load of about Max/3 in the centre and in four positions on the load receptor. Measuring the air temperature is recommended, and for the lowest uncertainties also the barometric pressure and a check of the temperature difference between the weights and the instrument (convection).

WEIGHTS (cg-18, 4.3.1). Standard weights shall be traceable to the SI unit of mass — by calibration with uncertainty or by confirmation that they are within maximum permissible errors. Weights complying with OIML R 111 meet the requirements for density, surface and magnetic properties; their maximum permissible errors or uncertainties shall be compatible with the scale interval d of the instrument and the client’s needs.

UNCERTAINTY AND CERTIFICATE (cg-18, clauses 7–8). The uncertainty of the error of indication comprises the contributions of the indication (resolution, repeatability, eccentricity) and of the reference mass (calibration of the weights, drift, air buoyancy, convection); the coverage factor k is chosen for a coverage probability of 95.45 %. The certificate gives, among others, indications or errors for the loads, the standard deviation, the result of the eccentricity test, the expanded uncertainty with k and the ambient conditions; a statement of conformity to a specification is optional — decision rules are described in ILAC-G8:09/2019.

MINIMUM WEIGHT (cg-18, Appendix G). The smallest sample quantity at which the relative uncertainty of the weighing result equals the accuracy required by the user (e.g. 0.1 %); it is derived from the global uncertainty of the weighing result established at calibration.

REGULATIONS. Directive 2014/31/EU concerns the making available on the market of non-automatic weighing instruments and distinguishes uses, among others commercial transactions, medical practice, the preparation of medicines on prescription in pharmacies and analyses in medical and pharmaceutical laboratories (Article 1(2)). Measuring instruments covered by Directive 2014/32/EU (MID) are other groups, including automatic weighing instruments.

WHAT WE DO NOT GIVE HERE. The cg-18 guideline does not set uncertainty limits or required ambient conditions (temperature, humidity) — the laboratory agrees them with the client; we therefore give no such figures and no acclimatisation times. The text of PN-EN 45501:2015 is not freely available — classes and maximum permissible errors are given according to OIML R 76-1:2006, which the cg-18 guideline cites interchangeably with EN 45501.

Method principle

Calibrating a balance means comparing its indications I with the reference values m_ref of test loads of known conventional mass: the error of indication E = I − m_ref is determined for at least five loads over the weighing range and reported with its expanded uncertainty. It is supplemented by the repeatability test (at least 5 depositions of the same load) and the eccentricity test (a load of about Max/3 in five positions). From the results the uncertainty of a weighing result in use and the minimum weight for the accuracy required by the user can be derived.

Applications

• Calibration of non-automatic weighing instruments of all accuracy classes (I, II, III, IIII) at their place of use
• Metrological traceability of weighing results in laboratories with a management system according to ISO/IEC 17025, ISO 9000 or ISO 10012 (addressees of the EURAMET cg-18 guideline)
• Determination of the minimum weight and of the uncertainty of a weighing result for the user’s requirements (EURAMET cg-18, Appendix G)
• Statement of conformity of a balance to the user’s specification with a decision rule (ILAC-G8:09/2019)
• Metrological requirements for the conformity assessment of balances used, among others, in trade, medicine and pharmacies (Directive 2014/31/EU, PN-EN 45501)

Key parameters

Standard

Standard number

PN-EN 45501:2015-05 / OIML R 76-1:2006

Title (PL)

Zagadnienia metrologiczne wag nieautomatycznych / Wagi nieautomatyczne — Część 1: Wymagania metrologiczne i techniczne — Badania

Title (EN)

Metrological aspects of non-automatic weighing instruments / Non-automatic weighing instruments — Part 1: Metrological and technical requirements — Tests

Step-by-step procedure

1. Preconditions

   Identification of the balance, check that its functions are free from contamination or damage and that the normal conditions of use (air currents, vibrations, stability of the weighing site) are suitable.

2. Preparation of the balance

   Energising for an appropriate period (e.g. the warm-up time specified by the manufacturer or set by the user), levelling, loading at least once to approximately the largest test load.

3. Adjustment

   A balance that the user regularly adjusts before use is adjusted before calibration — by the means normally applied by the client (internal or with an external weight), unless agreed otherwise.

4. Acclimatisation of weights

   Weights transported to the calibration site are acclimatised until the convection effect is negligible in view of the required uncertainty, or the effect is included in the uncertainty budget.

5. Repeatability test

   Zero setting, at least 5 depositions of the same load (at least 3 for ≥ 100 kg), recording of indications; after each removal the zero indication is checked.

6. Test for errors of indication

   At least 5 loads distributed over the range, e.g. zero or Min, 0.25 Max, 0.5 Max, 0.75 Max and Max; loading in steps with unloading or continuously increasing, depending on how the balance is used.

7. Eccentricity test

   A load of about Max/3 placed successively in the centre and in four positions (front left, back left, back right, front right); indications recorded.

8. Auxiliary measurements

   Air temperature near the balance, barometric pressure where needed, temperature difference between weights and balance; on high-resolution balances — check of magnetic interaction with a non-metallic spacer.

9. Uncertainty calculation

   Uncertainty of the error of indication from the contributions of the indication (resolution, repeatability, eccentricity) and of the reference mass (calibration, drift and buoyancy of the weights, convection); expanded uncertainty for 95.45 %.

10. Calibration certificate

    Indications or errors for the loads, standard deviation, eccentricity result, expanded uncertainty with k, ambient conditions, adjustment performed; optionally a statement of conformity to a specification with a decision rule (ILAC-G8:09/2019).

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• Heavy weights are carried by the handling devices provided for this purpose (knobs, handles, axles, hooks or eyes — OIML R 111, 6.3–6.4)

Frequently asked questions