The fourth article of Law 3/1985, of March 18, of Metrology, establishes in paragraph 3 that the patterns of the basic units declared as such, guarded, preserved and maintained by the State, will be the national of which all the others will be derived. In execution of the provisions of this precept, Royal Decree 648/1994, of 15 April, declares the national standards of measurement of the basic units of the International System of Units.

Once the national patterns of the basic units have been defined in the terms set out in the previous Royal Decree, it is appropriate to define the national patterns of the derived units that will serve as reference in all the metrological actions to be carried out. This process is carried out in phases to the extent that technological development and international comparisons made with organisms of other States competent in metrological matters permit. To this effect, the final provision of Royal Decree 648/1994, of 15 April, authorizes the Minister of Public Works, Transport and Environment, today Ministry of Public Works, to define the national patterns of the units derived from the International System of Units.

According to this, and by means of this Order, the national patterns of the derived units corresponding to the magnitudes of plane angle, density of solids, strength, pressure and volume are defined.

The unit of the plane angle magnitude belongs to the non-dimensional derived units, in accordance with the provisions of Article 3 of Royal Decree 1737/1997 of 20 November, amending Royal Decree 1317/1989, of 27 October, for which the Legal Units of Measure are established.

The unit of the magnitude of solids density, also called bulk mass, belongs to the group of derived units, listed in section 2.2 of Chapter II of the Annex to Royal Decree 1317/1989, of 27 October.

The units of force and pressure magnitudes belong to the group of derived units with special names and symbols, and thus are expressly related to Chapter II, Section 2.3 of the Annex to the Royal Decree. previously mentioned.

The unit of the volume size belongs to the group of authorized units, which are listed in Section 4.1 of Chapter IV of the Annex to the aforementioned Royal Decree 1317/1989.

It should be noted, finally, that the depositary and body responsible for the conservation of these derived units will be the Spanish Metrology Centre, which, in accordance with Article 100 of Law 31/1990 of 27 December 1990, State General Budget for 1991, which is the creator of this body, is entrusted, inter alia, with the custody and conservation of national standards of measurement.

In its virtue, I have:

Single item.

It is stated, for legal purposes, national patterns of the units derived from the International System of Units, those related in the Annex of this Order, with the technical characteristics in the indicated.

Final disposition.

This Order shall enter into force on the day following that of its publication in the "Official State Gazette".

Madrid, December 28, 1999.

MONTALVO ARIAS-SALGADO

ANNEX

1. National pattern corresponding to the plane angle magnitude.

The national pattern corresponding to the magnitude of the flat angle, whose unit is called radian (rad), is preserved, maintained and guarded by the Spanish Metrology Centre, and is carried out by means of a system consisting of a Rotary table based on an internal circular scale of high precision, of resolution equal to 0.04 '', and a measurement field of 0 rad at 2p rad, with a typical measurement uncertainty (for k= 1) of 0,05 '', i.e. 2,4 ^ 10-7 rad.

The flat angle is based, from the operational point of view, on the ratio of lengths or division of the circle.

In the first case, it materializes by generating small angles based on the trigonometric relationship existing between the sides of a rectangle triangle and one of the acute angles that form it. These sides possess perfectly known lengths and are drawn to the national pattern of length. In the second case, in any division of the circle that is established, the sum of the angles in the center is always equal to 2p rad. This principle is called a "circle close".

It is preserved by periodic comparisons made with flat-angle patterns of metrological organisms from other states.

2. National pattern corresponding to the magnitude of solids density.

The national pattern corresponding to the magnitude of solids density, also called mass in volume, whose unit is the kilogram per cubic meter (kg/m3), is preserved, maintained and guarded by the Spanish Center of Metrology, and is established from the national patterns of mass and length.

It is materialized by a perfectly polished quartz sphere, with a roundness defect of less than 500 nm, of 1 kilogram of mass, 90 millimeters of diameter and a coefficient of thermal expansion of 1,5 ^ 10-6 K-1. Density is determined through the knowledge of the mass and the volume of the sphere, with a typical relative uncertainty of 6 ^ 10-7 (for k= 1).

It is preserved by periodic comparisons made with solid density patterns of metrological organisms from other states.

3. National pattern corresponding to the magnitude of force.

The national pattern corresponding to the magnitude of force, whose unit is called newton (N), is preserved, maintained and guarded by the Spanish Metrology Center, and is obtained through the national pattern of the mass unit and of the measure of the acceleration of the local gravity.

It is materialized and preserved by means of three direct load force machines whose nominal values are 500 kN, 20 kN and 1 kN.

The typical relative measurement uncertainty (for k= 1) in the force generation field from 10 N to 500 kN is 1 ^ 10-5. This uncertainty has been established by the Advisory Committee for Mass and Related Measures (CCM) and has been established through participation in various international comparisons.

It is preserved by periodic comparisons made with force patterns of metrological organisms from other states.

4. National pattern corresponding to the pressure magnitude.

The national pattern corresponding to the magnitude of pressure, whose unit is the pascal (Pa), is preserved, maintained and guarded by the Spanish Metrology Center, and is derived from the national patterns of mass and length, together with with the measure of the acceleration of the local gravity.

This pattern is materialized as follows, depending on the measurement interval:

In the 10-6 Pa field up to 102 Pa, it is performed with a dynamic system through a known conductance hole.

In the field of 102 Pa up to 500 MPa, it is performed with a series of piston-cylinder assemblies, mounted in their corresponding pressure scales, on which different combinations of masses are charged. The pressures are determined both in absolute and relative mode, using as a means of transmission a gaseous or liquid fluid, depending on the range of measurement.

For ultra-high pressures, in relative mode, from 500 MPa to 1 GPa, it is performed through a pressure multiplier.

The typical relative measurement uncertainty (for k= 1) depends on the mode of performance and the pressure measurement interval on which you are working. For pressures from 10-6 Pa up to 102 Pa, it is 5 ^ 10-3; for pressures from 102 Pa up to 500 MPa, it is 30 ^ 10-6; and for pressures from 500 MPa to 1 GPa, it is 100 x 10-6.

It is preserved by periodic comparisons made with pressure patterns from metrological organisms in other states.

5. National pattern corresponding to the volume size.

The national pattern corresponding to the volume size, whose unit is the liter (l or L), is preserved, maintained and guarded by the Spanish Metrology Center, and is established from the national mass pattern.

It is materialized by a set of vessels-nominal capacity pattern of 1 L, 2 L, 5 L, 10 L, 20 L, 50 L and 100 L, constructed in stainless steel, internally coated with halar H + S, and in cylindrical-biconic form.

Typical measurement uncertainty (for k= 1) is 1 ^ 10-5 L.

It is preserved, in its different capacities, by periodic comparisons made with volume patterns of metrological organisms of other States.