Pattern approval for measuring instruments, Uncategorized
Pattern approval for measuring instruments
Courtesy: Pattern approval for measuring instruments
The Measuring Instruments Directive 2014/32/EU (the information is not updated and below this article refers to the old one 2004/22/EC), is a directive by the European Union, which seeks to harmonise many aspects of legal metrology across all member states of the EU. Its most prominent tenet is that all kinds of meters which receive a MID approval may be used in all countries across the EU.
The MID covers these measuring instruments:
- Water meters
- Gas meters and volume conversion devices
- Active electrical energy meters
- Heat meters
- Measuring systems for the continuous and dynamic measurement of quantities of liquids other than water
- Automatic weighing instruments
- Taximeters
- Material measures
- Dimensioning systems
- Exhaust gas analysers
A beer glass with a fill line in compliance with the MID
Measuring instruments that comply with the MID bear:
- the CE mark
- a capital letter “M” and the last two digits of the year of its affixing, surrounded by a rectangle
- the identification number of the notified body involved in conformity assessment
The Measuring Instruments Directive was published on 30 April 2004 in the Official Journal of the EU, but not applied until after 30 October 2006 and there will be a 10-year transition period. National implementations of the new legislation are currently in the works.
Two amendments of the Directive were published:
COMMISSION DIRECTIVE 2009/137/EC of 10 November 2009 Amending Directive 2004/22/EC of the European Parliament and of the Council on measuring instruments in respect of exploitation of the maximum permissible errors, as regards the instrument-specific annexes MI-001 to MI-005 and
Directive 2014/32/EU of the European Parliament and of the council of 26 February 2014 on the harmonisation of the laws of the Member States relating to the making available on the market of measuring instruments
In the field of industrial ultrasonic testing, ultrasonic thickness measurement (UTM) is a method of performing non-destructive measurement (gauging) of the local thickness of a solid element (typically made of metal, if using ultrasound testing for industrial purposes) based on the time taken by the ultrasound wave to return to the surface. This type of measurement is typically performed with an ultrasonic thickness gauge.
Ultrasonic waves have been observed to travel through metals at a constant speed characteristic to a given alloy with minor variations due to other factors like temperature. Thus, given this information, called celerity, one can calculate the length of the path traversed by the wave using this formula:
{\displaystyle l_{m}=ct/2}
where
{\displaystyle l_{m}}
{\displaystyle c}
{\displaystyle t}
The formula features division by two because usually the instrumentation emits and records the ultrasound wave on the same side of the sample using the fact that it is reflected on the boundary of the element. Thus, the time corresponds to traversing the sample twice.
The wave is usually emitted by a piezoelectric cell or EMAT sensor that is built into the measurement sensor head and the same sensor is used to record the reflected wave. The sound wave has a spherical pattern of propagation and will undergo different phenomena like multipath reflection or diffraction. The measurement does not need to be affected by these since the first recorded return will normally be the head of the emitted wave traveling at the shortest distance which is equivalent to the thickness of the sample. All other returns can be discarded or might be processed using more complicated strategies.
