Measuring Instruments Directive: An Essential Guide

The Measuring Instruments Directive sets design and manufacturing requirements for measuring instruments sold in the European Union.The goal is to ensure that measuring instruments provide a high level of quality concerning the measurement data, such as temperature, weight, or volume.

This guide explains how the directive applies to instruments such as water meters, taximeters, and exhaust gas analysers. It also provides examples of harmonised standards, as well as requirements related to documentation, labelling, and more.

What is the Measuring Instruments Directive?

This directive establishes requirements for measuring instruments used in trade, consumer, and industrial contexts. These requirements aim to ensure that the instruments are accurate and promote fairness and transparency in transactions.

Here are some of the key requirements under the Measuring Instruments Directive:

• Compliance with the essential requirements listed in Annex I and harmonised standards
• Completion of conformity assessments procedure
• Provision of a Declaration of Conformity
• Provision of technical documentation
• Provision of instructions and safety information
• Affixation of the CE marking, metrology marking, and traceability information to the product
• Provision of inscriptions on the measuring instrument

Which products are covered by the Measuring Instruments Directive?

The directive defines a ‘measuring instrument’ as a device or system that you can use to perform measurements. The following types of instruments are mentioned in Article 2:

• Water meters (MI-001),
• Gas meters and volume conversion devices (MI-002)
• Active electrical energy meters (MI-003)
• Thermal energy meters (MI-004)
• Measuring systems for continuous and dynamic measurement of quantities of liquids other than water (MI-005)
• Automatic weighing instruments (MI-006)
• Taximeters (MI-007)
• Material measures (MI-008)
• Dimensional measuring instruments (MI-009)
• Exhaust gas analysers (MI-010).

Each category is covered by specific requirements listed in Annexes III to XII. These apply in addition to the general requirements that apply to all covered measuring instruments.

Product examples

Here are other examples of measuring instruments covered by the directive:

• Water meters
• Gas meters
• Active electrical energy meters
• Thermal energy meters
• Systems for measuring non-water liquids
• Automatic weighing instruments
• Taximeters
• Material measures
• Dimensional measuring instruments
• Exhaust gas analysers

What are the requirements set by the MID?

This section lists the essential requirements set by Annex I of the directive:

a. Allowable errors – For example, the error of a gas meter should not exceed the maximum permissible error set by its instrument-specific requirements (Annex IV).

b. Reproducibility – For example, a gas meter that returns the same result while measuring the amount of gas produced under the same conditions.

c. Repeatability – For example, a taximeter that shows the same fare for identical trips.

d. Discrimination and sensitivity – For example, a scale that detects tiny changes in weight.

e. Durability – For example, an energy meter that works accurately for years.

f. Reliability – For example, a measuring tool that gives accurate results every time.

g. Suitability – For example, a heat meter that is made to measure heating systems properly.

h. Protection against corruption – For example, an exhaust analyser that cannot be easily tampered with.

i. Information to be borne by and to accompany the instrument – For example, a water meter that shows its model and maker.

j. Indication of result – For example, a beer glass that shows the exact volume poured.

k. Further processing of data to conclude the trading transaction – For example, a gas meter that records the measurement data.

l. Conformity evaluation – Measuring instruments must be designed in a manner that allows to evaluate their conformity with the applicable requirements.

Standards

Covered products must normally comply with harmonised standards in order to prove that the product complies with the requirements set by the directive. There are several standards harmonised under the Measuring Instruments Directive. Here are some examples:

EN 1359 – Gas meters – Diaphragm gas meters

EN 12261 – Gas meters – Turbine gas meters

EN 12405-1 – Gas meters – Conversion devices – Part 1: Volume conversion

EN 14236 – Ultrasonic domestic gas meters

EN 62058-11 – Electricity metering equipment (a.c.) – Acceptance inspection – Part 11: General acceptance inspection methods

EN 62058-21 – Electricity metering equipment (a.c.) – Acceptance inspection – Part 21: Particular requirements for electromechanical meters for active energy (classes 0,5, 1 and 2 and

EN 62058-31 – Electricity metering equipment (a.c.) – Acceptance inspection – Part 31: Particular requirements for static meters for active energy (classes 0,2 S, 0,5 S, 1 and 2, and class indexes A, B and C)

EN 62059-32-1 – Electricity metering equipment – Dependability – Part 32-1: Durability – Testing of the stability of metrological characteristics by applying elevated temperature

Conformity assessment procedure

Per Article 17, the manufacturer should choose one of the conformity assessment procedures that is listed in the instrument-specific Annex to assess that instrument’s conformity.

Some of these procedures require a third-party assessment carried out by a notified body, that is, an EU-designated independent organisation that assesses product conformity.

This section provides two tables:

a. The first table lists the different available conformity assessment modules, and whether you need a notified body to carry it out.

b. The second table lists the available conformity assessment procedures, which are composed of one or more modules.

Conformity assessment module	Notified body required?
Module A – Internal Production Control	No
Module A2 – Internal Production Control Plus Supervised Instrument Checks At Random Intervals	Yes (unless an accredited in-house body is used for periodic checks)
Module B – EU-type Examination	Yes
Module C – Conformity To Type Based On Internal Production Control	No
Module C2 – Conformity To Type Based On Internal Production Control Plus Supervised Instrument Checks At Random Intervals	Yes (unless an accredited in-house body is used for periodic checks)
Module D – Conformity To Type Based On Quality Assurance Of The Production Process	Yes
Module D1 – Quality Assurance Of The Production Process	Yes
Module E – Conformity To Type Based On Instrument Quality Assurance	Yes
Module E1 – Quality Assurance Of Final Instrument Inspection And Testing	Yes
Module F – Conformity To Type Based On Product Verification	Yes
Module F1 – Conformity Based On Product Verification	Yes
Module G – Conformity Based On Unit Verification	Yes
Module H – Conformity Based On Full Quality Assurance	Yes
Module H1 – Conformity Based On Full Quality Assurance Plus Design Examination	Yes

Note: Accredited in-house bodies should meet the requirements listed in Article 30 of the directive.

The following table lists which conformity assessment should be carried out for each covered product category:

Product type	Conformity assessment module
Water meters	B + F or B + D or H1
Gas meters and volume conversion devices	B + F or B + D or H1
Active electrical energy meters	B + F or B + D or H1
Thermal energy meters	B + F or B + D or H1
Measuring systems for the continuous and dynamic measurement of quantities of liquids other than water	B + F or B + D or H1 or G
Automatic weighing instruments	For mechanical systems: B + D or B + E or B + F or D1 or F1 or G or H1 For electromechanical instruments: B + D or B + E or B + F or G or H1 For electronic systems or systems containing software: B + D or B + F or G or H1
Taximeters	B + F or B + D or H1
Material measures	For material measures of length: F 1 or D1 or B + D or H or G For capacity serving measures: A2 or F1 or D1 or E1 or B + E or B + D or H
Dimensional measuring instruments	For mechanical or electromechanical instruments: F1 or E1 or D1 or B + F or B + E or B + D or H or H1 or G For electronic instruments or instruments containing software: B + F or B + D or H1 or G
Exhaust gas analysers	B + F or B + D or H1

Note: Although Module A is mentioned by the directive, we could not find a conformity assessment procedure that lists it.

Declaration of Conformity

The manufacturer should create the Declaration of Conformity to:

• State that the measuring instrument meets the essential requirements in Annex I, and
• Indicate compliance with the requirements set in the instrument-specific Annexes

The Declaration of Conformity must contain the following items as set out in Annex XIII:

• The instrument model (e.g. product batch, type, serial number)
• Manufacturer name and address (and authorised representative, where applicable)
• The declaration statement
• Object of declaration (e.g. an image of the instrument)
• The conformity statement
• References to relevant harmonised standards or technical specifications used
• Statement identifying the notified body, where applicable
• “Signed for and on behalf of” information

If a measuring instrument falls under multiple regulations or directives needing an EU declaration of conformity, you should use one declaration for all applicable regulations and directives.

Importers and manufacturers should ensure that a copy of the Declaration of Conformity accompanies the measuring instrument.

Technical documentation

Manufacturers should create the technical documentation, which should clearly explain how the measuring instrument is designed, made, and works.

The technical documentation should contain:

• General description of the measuring instrument
• Concept designs, manufacturing drawings, and plans of components and sub-assemblies
• Manufacturing processes
• Description of electronic devices with drawings and diagrams, if applicable
• Descriptions and explanations of the concept designs, manufacturing processes, and electronic devices, as well as how the measuring instrument operates
• List of harmonised standards applied
• Descriptions of how the requirements were met if harmonised standards were not utilised, and a list of applied technical specifications
• Results of examinations and design calculations
• Test results to demonstrate compliance with the directive’s requirements or durability specifications
• EU-type examination certificates, or EU design examination certificates

The manufacturer should also specify:

• The location of applied seals and markings
• The conditions for compatibility with sub-assemblies and interfaces, where applicable

Instructions and safety information

The directive requires manufacturers to provide the instructions and information listed in point 9.3 of Annex I:

a. Rated operating conditions

b. Mechanical and electromagnetic environment classes

c. Maximum and minimum temperature limit, possibility of condensation, open or closed location

d. Instructions for installation, maintenance, repairs, and allowable adjustments

e. Instructions for operating the measuring instrument correctly, and any special conditions of use

f. Conditions for the compatibility with interfaces, measuring instruments, or sub-assemblies

CE marking

The CE marking indicates that the manufacturer has complied with the applicable requirements. The manufacturer should permanently affix the CE marking to the measuring instrument or its data plate, or the accompanying documents – e.g. the instructions booklet and the packaging.

The CE marking should be followed by:

a. The supplementary metrology markings

b. The notification body’s identification (where applicable)

c. Other marks that indicate a special use or risk

Supplementary metrology marking

The supplementary metrology marking:

• Consists of the capital letter “M” and the last two digits of the year the marking was affixed
• Is surrounded by a rectangle

This marking should follow the CE marking.

Traceability information

The directive requires you to ensure that your measuring instrument bears the following traceability information:

• Product type, batch, or serial number
• Company name, registered trade name, or registered trade mark
• Company postal address

If the size of the measuring instrument does not permit this, you should provide the information in both a document accompanying the product and the packaging.

Inscriptions

The measuring instrument should bear the following inscriptions, if relevant:

a. The manufacturer’s name, registered trade name or trade mark

b. Information about the accuracy of its measurements

c. Information about usage conditions

d. Measuring capacity

e. Measuring range

f. Identity marking

g. EU-type (or EU design) examination certificate number

h. Details on whether additional devices meet the directive’s legal metrological control provisions

If the measuring instrument is too small or delicate to display the required information, you should properly mark its packaging and accompanying documents.

Product testing

The directive mandates that you get your measuring instruments tested against the essential requirements and relevant harmonised standards to ensure they are accurate, and reliable.

If your measuring instrument passes testing, you should receive a test report proving compliance with the requirements. Here are some examples of companies that claim to test against the directive’s requirements:

• Bureau Veritas
• Eurolab
• Tecnalia
• IMQ

Notified Bodies

You can find notified bodies that provide services according to the directive requirements on the EU’s NANDO database. Here are some examples:

• Labor S.A.
• AS Metrosert
• Kema B.V.
• NMi Certin B.V.
• Cesky Metrologicky Institut