Laboratory work № 6

Elements of metrological certification of measuring instruments for compliance with technical standards

1. Work goal

1.1. The study of the basic concepts of certification tests of measuring instruments (MI).

1.2. The formation of skills of determining the structure of the MI error for all numerical scale markings.

1.3. Mastering the skills of metrological certification of MI, in a separate division of the scale in the particular conditions.

2. Main principles

2.1. Basic concepts of product certification

Certification in translation from Latin means "is done right."

Certification – is the process by which a third part gives written assurance that a product, process or service fulfills specified requirements.

Certification is considered the basic concept of reliable proof of correspondence of production (process, service) to specified requirements. Generally accepted concept of such proof is the certification of compliance.

Certification of compliance through certification provides mandatory involvement of the third part. This certification of compliance is independent and runs on rules of certain procedure; it ensures compliance with specified requirements.

Certification of compliance – is an action of testing laboratory of a third part, which proves, that a particular sample corresponds the specific standard or other normative document.

Procedures, regulations, testing and other activities that can be considered as part of the process (activity) of certification can be different depending on several factors. Among them - the legislation on standardization, quality and certification directly; features of the object of certification, which in turn determines the selection of the test method, etc. In other words, the proof of compliance is carried out by one or the other system of certification.

In correspondence with ISO / MEK documents, the certification system - is a system that has its own rules, procedures and management for carrying out certification of conformity. It can operate at the national, regional and international levels.

If the system of certification is engaged in proof of compliance of certain type of product (process, service) – it is a system of certification of homogeneous product (certification program, certification scheme), which uses in its own practice standards, rules and procedure that are specific to the product.

A systematic review of the degree of compliance with specified requirements is called conformity assessment. More common notion of conformity assessment is regarded inspection, which is considered as the conformity assessment by measuring the specific characteristics of the product.

2.2 Measuring instruments and their metrological characteristics

Measuring instruments (MI) - are the technical tools used in the measurements and which have normalized metrological characteristics (NMC). MI are divided into measures, measuring devices, measuring transducers, auxiliary measuring facilities, measuring units and measuring systems.

Measure – is a measuring instrument that reproduces the physical quantity of a given size.

Measuring devices - are measuring instruments that are designed to produce the signal of measured information in a form accessible to direct perception of the observer.

All measuring instrument s have certain metrological characteristics. Measures are characterized by the nominal and actual values. Nominal value of the measure - is the value of quantity indicated on the extent or attributed to it. The actual value of the measure – is a real value, which is reproduced by measure.

Measuring devices consist of a sensor, which is under the direct influence of the physical quantity, measuring unit or a readout device. Readout device has a scale and a pointer, which is in the form of the material rod-arrow, or as a ray of light - a light pointer. The scale has a set of marks and affixed around some of them numbers of count that correspond to a set of consecutive values ​​of the quantity.

Scale interval – is a difference of values ​​of the quantity that corresponds two neighboring scale marks. Sensitivity of device is defined as the ratio of the output signal of the device to its induced changing of measured value.

Initial and final value ​​of the scale - is the smallest and largest value of measured quantity, which is defined on the scale.

Measurement range - is the range of the measured value, for which normalized errors of device are allowable. Measuring limits are the greatest or the least value of the measuring range.

The variation of parameters – is a difference of device’s parameters which correspond to a given point in the measurement range at two directions of slow measurements of device’s parameters.

Measuring stability - is the quality of measuring instrument that displays unchanging over time of its metrological characteristics.

Accuracy class of MI – is a summarized its characteristics, determined by the boundaries of acceptable and additional errors, and other properties of the measuring instruments. Accuracy class, although characterizes a set of the metrological characteristics of the given measuring instrument, but does not uniquely determine the accuracy of the measurement, since the latter depends on the measurement method and the conditions of their implementation.