Calibration and verification

There are a few questions that are asked more frequently. Here are answers to a selection of metrology related questions.

If you cannot find an answer to your question, please contact our customer service.

What does calibration mean?

Calibration is a procedure whereby under certain agreed conditions the value obtained with a measuring instrument can be linked to the respective value of the physical quantity realised with a measurement standard, i.e., the measurement error of the measuring instrument is determined. In simpler terms, it is determined by how much the measuring instrument “lies”, and the respective information is presented in the calibration certificate.

In layman’s terms, calibration is also often understood to mean adjustment, or the regulation of the reading of the measuring instrument; indeed, the English term “calibration” on the display or in the user manual of the measuring instrument often means adjustment. We also provide adjustment as an additional service, if possible and if desired by the customer.

What does verification mean?

Verification is a procedure whereby a competent verification laboratory inspects the conformity of a measuring instrument with the requirements established by law and marks the conforming measuring instrument with verification marks. The verification obligation is established by the state and failure to fulfil the obligation is a violation of law. See also answer to question which measuring instruments must be verified.

Which measuring instruments must be verified?

The verification obligation arises from the Metrology Act  and it only applies to measuring instruments used for certain purposes, e.g., in measurements performed upon concluding transactions, in trade, in state supervision. A list of the types of measuring instruments subject to the verification obligation together with the verification validity periods and the normative documents establishing requirements is provided in a regulation of the Minister of Economic Affairs and Infrastructure.

Not every measuring instrument can be verified. For verification, the type of a measuring instrument must be tested and declared to be of sufficient quality so that it can be presumed to function correctly during verification intervals. In the European legal landscape, different requirements apply to different measuring instruments – you can refer to Metrosert’s specialists about requirements to specific measuring instruments.

How often must measuring instruments be verified?

The verification validity period is the shortest for evidentiary breathalysers – 6 months –, while the longest period is “limitless”, which substantively means that there is only the initial verification obligation. This is the case for glass capacity measures, for instance. The verification validity periods of the remaining measuring instruments largely fall within one to five years. The verification validity periods of measuring instruments subject to the verification obligation are provided in an annex to Regulation No. 65 from 18.12.2018 of the Minister of Economic Affairs and Infrastructure.

How often must measuring instruments be calibrated?

The frequency of calibration of measuring instruments is chosen by the user of the measuring instrument on the basis of the recommendations provided in standards or other normative documents, the manufacturer’s recommendations, the terms and conditions of use, and other factors that may alter the metrological parameters of the measuring instrument.

What does an accredited calibration laboratory mean?

Measuring instruments must be calibrated so that the traceability of the measurements performed with them is ensured to international or national measurement standards. The calibration of measurement instruments at an accredited calibration laboratory gives the best guarantee of this.

Accreditation is the assessment of the conformity of testing and calibration laboratories with the requirements of the relevant international standards by an independent third person. In Estonia, laboratories are accredited by the Estonian Centre for Standardisation and Accreditation. Calibration laboratories are assessed in accordance with standard EVS-EN ISO/IEC 17025:2017. Upon ordering calibration from a non-accredited laboratory, the person ordering the service must ascertain the reliability of the laboratory. In various fields of activity, it is namely the calibration of measuring instruments at an accredited laboratory that is the precondition to their use.

In what extent and how precisely must measuring instruments be calibrated?

To calibrate an instrument, you need to choose a laboratory with the appropriate measuring capability in the given field, i.e., the laboratory must be capable of calibrating the measuring instrument accuretely enough and to the sufficient range.

For calibration to be of use in deciding the suitability of a measuring instrument for use, calibration points must cover the part of the measuring range that is used. According to good practice, at least three calibration points must be chosen in the measuring range used, covering the beginning, end and middle of the range. Metrosert’s calibration prices generally include at least three calibration points, and if required, as many points as necessary can be ordered additionally.

Upon ordering a calibration service, make sure that the measuring capability of the calibration laboratory is sufficiently good, or the measurement uncertainty achieved in calibration is sufficiently small. In the absence of other information, you may rely on the accuracy data of the manufacturer of the measuring instrument, making sure that the calibration laboratory is able to ensure a measurement uncertainty of the calibration method that is at least three times smaller.

If a measuring instrument “lies”, will Metrosert adjust the instrument upon calibration, to ensure it is more accurate?

Metrosert’s primary objective in inspecting a measuring instrument is to determine the measurement error of the instrument, i.e., we provide information on “how much it lies”. If the customer so wishes and it is technically possible, we will adjust the measuring instrument so as to make the measurement errors as small as possible. This is called adjustment.

How long does the calibration/verification of a measuring instrument at Metrosert take? When will I get my measuring instrument back?

If the customer has previously not been informed of any differences in the term for fulfilling the order and/or unless agreed otherwise with the customer, orders are generally fulfilled within five working days from the working day following the day or receipt of the measuring instruments or precious metal articles/materials at Metrosert. If it takes longer to fulfil an order, the customer’s representative will be notified of such upon accepting the job. If possible and upon agreement we fulfil orders faster. The customer’s representative will be notified when the work is completed.

What is measurement uncertainty?

According to the Estonian metrology terminology standard, measurement uncertainty means “a non-negative parameter characterising the dispersion of the values attributed to a measured quantity based on the existing information”, i.e., uncertainty provides an assessment of the accuracy of the measurement result in the form of a ± range which surrounds the measurement result and in which the measurement result may be. The smaller the uncertainty, the more accurate the measurement.

Uncertainty is calculated according to defined rules – the main basics are, for instance, described in the guidelines “Guide to the Expression of Uncertainty in Measurement (GUM)” issued in cooperation between ISO and BIPM, as well as in all metrology textbooks.

Metrosert regularly conducts training in the calculation of measurement uncertainty – see our training schedule.

Does Metrosert undertake the repair, disassembly or installation of measuring instruments?

Metrosert does not repair measuring instruments. If you suspect that your instrument is not working properly, bring it for calibration: we shall perform measurements and issue a measurement report or a notice of the measuring instrument not being in working order. Sometimes, an adjustment of the instrument is enough to bring it into working order. If repairs are necessary, we will recommend a repair service provider, if possible.