FAQ

Legal metrology covers a set of requirements and control procedures imposed by the State to guarantee the accuracy of certain measuring instruments (scales, fuel pumps, taxi meters, etc.) in order to ensure consumer protection, fair trade and the proper application of laws and regulations.

Industrial metrology covers the set of techniques serving to take measurements, ensure their accuracy, and interpret them.

For manufacturers, ensuring the traceability and accuracy of their measurements is essential for controlling their manufacturing procedures and monitoring the quality of their products.

Metrology can therefore contribute a great deal to a company’s competitiveness.

The International Vocabulary of Metrology (VIM) defines verification (§2.44) as “provision of objective evidence that a given item fulfils specified requirements.”

The International Vocabulary of Metrology (VIM) defines calibration (§2.39) as an “operation that, under specified conditions, in a first step, establishes a relation between the quantity values with measurement uncertainties provided by measurement standards and corresponding indications with associated measurement uncer¬tainties and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication.”

Calibration serves to appreciate any error in measurement of an instrument and, if the instrument is inexact, to compensate the error by making an adjustment.
Verification serves to establish that a measurement error is smaller than an error known as the maximum permissible error. The maximum permissible error is defined by users as the greatest error they are prepared to accept.

Our team of metrologists carries out calibration and verification for the following physical quantities:

• forces/torques/testing machines
• mass/weighing/Leviatys® weighing
• pressure
• dimensions
• temperature/humidity
• special testing devices.

MPE is the maximum permissible error.

A weighing instrument takes account of the local value of gravity and levelling on the support. Consequently it is strongly recommended that scales should not be verified in a place and on a support other than in the customary place of use. Weighing accreditation is valid only for services carried out on-site.

Class 1 testing machines as per NF EN ISO 7500-1 have an instrumental bias of < 1% of the force applied and a repeatability error of ≤ 1% of the value read.

Class 2 testing machines as per NF EN ISO 7500-1 have an instrumental bias of < 2% of the force applied and a repeatability error of ≤ 2% of the value read.

The quality of test results for concrete specimens depends on compliance with a number of criteria regarding the performance of the test frame and the force applied:

• correct installation and anchoring of the machine;
• trueness and repeatability of the force indicator;
• operation of the ball joint (force transfer criteria);
• flatness of platens;
• hardness of platens;
• rate of loading.

The procedure consists in verifying that the product is subject to a lateral force of 3 daN per linear metre ± –0.5 daN per linear metre.

In the mesh of a sieve, the dimension of the aperture in one direction is known as the ‘weft’ and the dimension in the other direction is known as the ‘warp’.

If parameters A5 and A6 associated with verification of the performance of the ball joint are not conform, it is recommended that maintenance be carried out (removal, clearing of concrete dust and particles, and light lubrication of the ball joint).

The verification is carried out with a special sensor with four separate strain-gauge bridges. The shape and size of the sensor simulate a 16×32 concrete specimen. It will detect whether the force is applied uniformly to the concrete specimen or if the force is imbalanced in a direction to be determined.

The average time the CERIB metrology department takes to send calibration certificates and verification declarations is around 8 to 10 days.

A COFRAC Testing No. 1.0001 verification report issued by CERIB for testing machines (scope available at www.cofrac.fr) guarantees traceability back to international standard measures, compliance with best practice in respect of the testing field concerned, and validation by COFRAC of the declared measurement uncertainties. In general, verification of a testing machine combines the verification of several parameters such as the trueness of the load indicator and also the quality of the loading parts (dimensions, flatness, hardness, etc.).

For information purposes standard NF EN 932-5 concerning the general properties of aggregates, ‘Common equipment and calibration’, recommends the following frequencies: