Measuring Instruments Directive software
Software examination as part the type approval of measuring instruments used for trade under the measuring instruments directive which software are we talking about?
Software that is critical for the metrological characteristics of the measuring instrument.
What does used for trade mean?
It means that goods are sold by a quantity that is measured by the instrument in question, e.g. weight, length, volume.
What is the Measuring Instruments Directive?
It is an EU directive that will control a wide range of measuring instruments. It is in its draft stage at present and it is anticipated that it will come into force in 2006. It is commonly known as the MID.
Which measuring instruments will the MID control?
The MID will control the measuring instruments listed below. It is the responsibility of each member state to decide which instruments should be prescribed in that state. If an instrument is prescribed, then it should be examined under the requirements of the MID. Those instruments with asterisks against them are prescribed in the UK and will require type examination before they can be used for trade in the UK.
- Water meters (hot and cold*)
- Gas meters* and volume conversion devices*
- Electrical energy meters*
- Heat meters
- Measuring systems for quantities of liquids other than water (systems prescribed in the UK are liquid fuel delivered from road tankers* and fuel dispensers*)
- Automatic weighing instruments*
- Taximeters* (regulated by Local Authorities only, especially London)
- Material measures (material measures of length, capacity serving measures)
- Dimensional measuring instruments
- Exhaust gas analysers*
Why all the fuss about software?
The MID contains several requirements concerning software. Because the MID will be law, these requirements must be met in a prescribed measuring instrument used for trade. When new patterns are submitted for type approval under the MID, the software will be examined to ensure it meets the requirements of the MID.
What are the MID's requirements for software?
Briefly, software that is critical for the metrological characteristics shall be identifiable, shall be secured, shall not be inadmissibly influenced by other software and shall be adequately protected against accidental or intentional corruption. Software that is critical for the metrological characteristics is often known as legally relevant software.
How can I be sure that my software meets these requirements?
WELMEC has produced a software guide (7.2) for manufacturers, examiners and inspectors. The aim of the guide is to produce an expanded set of requirements, together with comments and acceptable solutions that, if met, will ensure approval of the software during type examination. The Guide is meant to reflect best practice.
Do I have to follow the WELMEC 7.2 guide?
No. A manufacturer can decide for himself how his software might meet the MID requirements. The WELMEC 7.2 guide was produced to show which aspects should be considered and how they might be resolved.
Where can I find the WELMEC 7.2 guide?
What does the WELMEC 7.2 guide say?
The Guide is modular and describes the requirements for two classes of measuring instrument plus a series of extensions applicable to one or both classes. The instrument classes are currently known as Type P, a stand-alone, built-for-purpose instrument with embedded software and Type U, where the instrument is built around a universal computer (general-purpose computer). The extensions cover the requirements for long-term storage, software separation, software download, transmission of legally relevant data via communications networks and instrument-specific requirements. Apart from the instrument-specific requirements, the requirements are generic and are based on risk classes, which are described in the Guide.
Will the software examination raise the cost of type approval?
Slightly. The Guide will put the software examination on a more formal basis since one of its aims is to harmonise software examination throughout Europe. Most of the additional effort is likely to fall on the manufacturer in preparing his documentation for the type approval examination. NMO already examines software as part of the type approval process but a small amount of additional necessary work has been identified from the Guide. Any increase in costs should be small for manufacturers following best practice.