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A measuring instrument shall provide a high level of metrological protection in order that any party affected can have confidence in the result of measurement, and shall be designed and manufactured to a high level of quality in respect of the measurement technology and security of the measurement data.
The essential requirements that shall be met by measuring instruments are set out below and are supplemented, where appropriate, by specific instrument requirements in Annexes III to XII that provide more detail on certain aspects of the general requirements.
The solutions adopted in the pursuit of the essential requirements shall take account of the intended use of the instrument and any foreseeable misuse thereof.
| Measurand | The measurand is the particular quantity subject to measurement. |
| Influence quantity | An influence quantity is a quantity that is not the measurand but that affects the result of measurement. |
| Rated Operating Conditions | The rated operating conditions are the values for the measurand and influence quantities making up the normal working conditions of an instrument. |
| Disturbance | An influence quantity having a value within the limits specified in the appropriate requirement but outside the specified rated operating conditions of the measuring instrument. An influence quantity is a disturbance if for that influence quantity the rated operating conditions are not specified. |
| Critical change value | The critical change value is the value at which the change in the measurement result is considered undesirable. |
| Material Measure | A material measure is a device intended to reproduce or supply in a permanent manner during its use one or more known values of a given quantity. |
| Direct sales | A trading transaction is direct sales if:
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| Climatic environments | Climatic environments are the conditions in which measuring instruments may be used. To cope with climatic differences between the Member States, a range of temperature limits has been defined. |
| Utility | A utility is regarded as a supplier of electricity, gas, thermal energy or water. |
Unless stated otherwise in the instrument-specific annexes, MPE is expressed as a bilateral value of the deviation from the true measurement value.
Where the instrument is intended to be used in a specified permanent continuous electromagnetic field the permitted performance during the radiated electromagnetic field-amplitude modulated test shall be within MPE.
The manufacturer shall specify the upper temperature limit and the lower temperature limit from any of the values in Table 1 unless otherwise specified in the Annexes III to XII, and indicate whether the instrument is designed for condensing or non-condensing humidity as well as the intended location for the instrument, i.e. open or closed.
| Temperature Limits | ||||
|---|---|---|---|---|
| Upper temperature limit | 30 °C | 40 °C | 55 °C | 70 °C |
| Lower temperature limit | 5 °C | – 10 °C | – 25 °C | – 40 °C |
Mechanical environments are classified into classes M1 to M3 as described below.
| M1 | This class applies to instruments used in locations with vibration and shocks of low significance, e.g. for instruments fastened to light supporting structures subject to negligible vibrations and shocks transmitted from local blasting or pile-driving activities, slamming doors, etc. |
| M2 | This class applies to instruments used in locations with significant or high levels of vibration and shock, e.g. transmitted from machines and passing vehicles in the vicinity or adjacent to heavy machines, conveyor belts, etc. |
| M3 | This class applies to instruments used in locations where the level of vibration and shock is high and very high, e.g. for instruments mounted directly on machines, conveyor belts, etc. |
The following influence quantities shall be considered in relation with mechanical environments:
vibration;
mechanical shock.
Electromagnetic environments are classified into classes E1, E2 or E3 as described below, unless otherwise laid down in the appropriate instrument-specific annexes.
| E1 | This class applies to instruments used in locations with electromagnetic disturbances corresponding to those likely to be found in residential, commercial and light industrial buildings. |
| E2 | This class applies to instruments used in locations with electromagnetic disturbances corresponding to those likely to be found in other industrial buildings. |
| E3 | This class applies to instruments supplied by the battery of a vehicle. Such instruments shall comply with the requirements of E2 and the following additional requirements:
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The following influence quantities shall be considered in relation with electromagnetic environments:
voltage interruptions;
short voltage reductions;
voltage transients on supply lines and/or signal lines;
electrostatic discharges;
radio frequency electromagnetic fields;
conducted radio frequency electromagnetic fields on supply lines and/or signal lines;
surges on supply lines and/or signal lines.
voltage variation;
mains frequency variation;
power frequency magnetic fields;
any other quantity likely to influence in a significant way the accuracy of the instrument.
Essential requirements specified in points 1.1 and 1.2 shall be verified for each relevant influence quantity. Unless otherwise specified in the appropriate instrument-specific annex, these essential requirements apply when each influence quantity is applied and its effect evaluated separately, all other influence quantities being kept relatively constant at their reference value.
Metrological tests shall be carried out during or after the application of the influence quantity, whichever condition corresponds to the normal operational status of the instrument when that influence quantity is likely to occur.
According to the climatic operating environment in which the instrument is intended to be used either the damp heat-steady state (non-condensing) or damp heat cyclic (condensing) test may be appropriate.
The damp heat cyclic test is appropriate where condensation is important or when penetration of vapour will be accelerated by the effect of breathing. In conditions where non-condensing humidity is a factor the damp-heat steady state is appropriate.
The application of the same measurand in a different location or by a different user, all other conditions being the same, shall result in the close agreement of successive measurements. The difference between the measurement results shall be small when compared with the MPE.
The application of the same measurand under the same conditions of measurement shall result in the close agreement of successive measurements. The difference between the measurement results shall be small when compared with the MPE.
A measuring instrument shall be sufficiently sensitive and the discrimination threshold shall be sufficiently low for the intended measurement task.
A measuring instrument shall be designed to maintain an adequate stability of its metrological characteristics over a period of time estimated by the manufacturer, provided that it is properly installed, maintained and used according to the manufacturer’s instruction when in the environmental conditions for which it is intended.
A measuring instrument shall be designed to reduce as far as possible the effect of a defect that would lead to an inaccurate measurement result, unless the presence of such a defect is obvious.
When a measuring instrument has associated software which provides other functions besides the measuring function, the software that is critical for the metrological characteristics shall be identifiable and shall not be inadmissibly influenced by the associated software.
Software identification shall be easily provided by the measuring instrument.
Evidence of an intervention shall be available for a reasonable period of time.
manufacturer’s name, registered trade name or registered trade mark;
information in respect of its accuracy;
and, where applicable:
information in respect of the conditions of use;
measuring capacity;
measuring range;
identity marking;
number of the EU-type examination certificate or the EU design examination certificate;
information whether or not additional devices providing metrological results comply with the provisions of this Directive on legal metrological control.
rated operating conditions;
mechanical and electromagnetic environment classes;
the upper and lower temperature limit, whether condensation is possible or not, open or closed location;
instructions for installation, maintenance, repairs, permissible adjustments;
instructions for correct operation and any special conditions of use;
conditions for compatibility with interfaces, sub-assemblies or measuring instruments.
the measurement is non-repeatable; and
the measuring instrument is normally intended for use in the absence of one of the trading parties.
A measuring instrument shall be designed so as to allow ready evaluation of its conformity with the appropriate requirements of this Directive.