Metrology concept

MEROS and legally controlled meters - VERIFICATION of specified blood pressure measuring instruments.

MEROS and non legally controlled meters - CALIBRATION of electrical quantities, frequency, time, rotational speed, lenght, temperature, relative humidity and pressure. Accreditation of Calibration issued on the basis of assessment of fulfillment of the accreditation criteria in accordance with ČSN EN ISO/IEC 17025:2005. Accredited by Czech Accreditation Institute Public Service Company.

Legally controlled meters ( verification )
Each country regulate the legal status of metrology its own laws. Legislative regulations are in the countries differ from each other and of course list of legally controlled meters can be different. Some measurements are so significant than only measuring instruments that meet specific requirements may be used. What measurements and what technical requirements must be meet is to be found in the legislation of the country. These are usually measuring instruments of consumption of electricity, gas, water, various billing measuring instruments etc. This can be found usually on the website of the National Metrology Institute. Legally controlled measuring instruments are verifies, other measuring instruments ( non legally controlled ) are calibrated. WARNING - This terminology may be different in different countries! Type approval process is very time-consuming and costly. For usage of legally cotrolled meter you have to discuss this matter with your relevant National Metrology Institute, however can be that the local metrological institute will require to make the entire approval process again.

Non legally controlled meters ( calibration )
Each country regulate the legal status of metrology its own laws. Legislative regulations are in the countries differ from each other and of course list of legally controlled meters can be different. Some measurements are so significant than only measuring instruments that meet specific requirements may be used. What measurements and what technical requirements must be meet is to be found in the legislation of the country. These are usually measuring instruments of consumption of electricity, gas, water, various billing measuring instruments etc. This can be found usually on the website of the National Metrology Institute. Legally controlled measuring instruments are verifies, other measuring instruments ( non legally controlled ) are calibrated. WARNING - This terminology may be different in different countries! Type approval process is very time-consuming and costly. For usage of legally cotrolled meter you have to discuss this matter with your relevant National Metrology Institute, however can be that the local metrological institute will require to make the entire approval process again. Non legally controlled meters ( calibration )

Difference between VERIFICATION of legally controlled meters and CALIBRATION of other of measuring instruments ( non legally controlled meters )
Calibration of measurement instruments is performed in accordance with EN 17025 standard and with common practices and rules in metrology. If the calibration certificate contains all requirements including confirmation of traceability of standards, it is internationally respected documents usually. Interval for next calibration is established by user of measurement instruments. Verification of legally controlled meters is performed according to specific rules, mostly by standards relating to the application ( type approval process ). Interval for next verification has legal basis.

Difference between CALIBRATION and ACCREDITED CALIBRATION
Accredited Calibration Laboratory offering accredited calibration is an independent laboratory that meets specified requirements and is permanently supervised. Accredited means permanent control of laboratory if meets the specified accreditation requirements in accordance with the relevant regulations applicable to the activity of an accredited Conformity Assessment Body ( fulfillment of the accreditation criteria in accordance with EN ISO/IEC 17025 ). Usually depends on the application of meter, legislation or on your internal regulations if is required accredited calibration. Calibration done by producer or calibration laboratory without accreditation meets only parts of them of is not accredited. Its calibration certificates are without mark ILAC-MRA and Accreditation mark. 

Difference between CALIBRATION and VALIDATION
The aim of calibration is the most accurate to describe the behavior of the device, the goal of validation is to quickly verify that the instrument is not wrong. Validation is usually done in the time between scheduled calibrations.

EXPIRATION DATE on the calibration certificate
Calibration certificate describes the characteristics of the device at the time of calibration and says nothing how the device will be measured in the future. Is written in the EN 17025 Article 5.10.4.4.: A calibration certificate ( or calibration label ) shall not contain any recommendation on the calibration interval except where this has been agreed with the customer. This requirement may be superseded by legal regulations. Accredited Calibration Laboratory does not write expiration time on your calibration certificates. Only based to customer written request can they put calibration interval to calibration certificate. The calibration interval is determined by the user the meter. This must be taken into consideration of legislative requirements and internal company regulations, manufacturer's recommendations which is given in the manual to the device, working conditions, rate of use of measuring instruments, level of service, the risks associated with exceeding out of accuracy of measurement. User can work with interval based information about trends from previous calibrations. If after several calibrations the meter remains deeply below acceptable limit, we can extend the calibration interval. If the trend is unfavorable, we must to reduce calibration interval. Repeated reduction of calibration interval indicates that the meter is not suitable for this application.

Metrological traceability of used standards
On each calibration certificate is introduced that MEROS has secured metrological traceability of standards and confirms it with signature. All the standards used during calibration are listed in calibration certificate together with their identification No., expiration date and Certificate of calibration No. to declare valid tracebility during calibration. If you find this argument as insufficient, ask us for calibration certificates for our standards. This is non-standard procedure and it is paid service. Not all calibration certificates of our etalons used during calibration are available in English, most of them are in Czech language..

Calibration in situ
Generally possible but we have to agree all required parameters of calibration. The advantages are: usually it is not necessary to shut down the equipment and calibration better describes state of measurement in the specific operating conditions of the device. The disadvantages are higher uncertainty than in the laboratory, often limited range of calibration and generally higher price ( it is necessary to arrive with special equipment ).

Uncertainty term on the calibration certificate
This term expresses the calibration uncertainty. It is not to measurement error or uncertainty of the device! The quality of the calibration depends on several independent things that are have different probabilities of occurrence (repeatability, uncertainty of standards, homogeneity of the temperature in the chambers, the resolution of the measuring instruments, the parasitic temperature dependences etc.). Using statistical methods are quantified these various effects and shall be included in resulting uncertainty, that is mentioned on the calibration certificate.

Evaluation of results on the calibration certificate
There are different ways to present the results on calibration certificates. MEROS always gives tables of measured values with their uncertainties. Generally, if the measurement error after adding uncertainty does not exceed the device specification, it is a statement that device "complies". If the measurement error itself is in the device specification, but after adding the uncertainty is out of limit, it is state "can not determine compliance or non-compliance." Other cases are already out of specification, the calibration certificate can not be created and the device can not be dispatched. If the measurement error does not exceed the specification, but after adding uncertainty is out of limit, then in case if the deviation is so small that the probability of device measured in its specification is greater than 95%, the calibration certificate is created and the device is dispatched.
 

Document EA4/02
This document describes the methodology for calculating of uncertainty in calibration. You can download it from here: http://www.european-accreditation.org/publication/ea-4-02-m