Calibration Services

S.A.M.A. Italia Srl is able to provide calibration reports compliant with the UNI CEI EN ISO/IEC 17025 standard and/or ACCREDIA certifications on the instruments it produces or those already part of your company’s instrument fleet.

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Differences Between Laboratory Test Reports and ACCREDIA Calibration Certificates

These services are designed to ensure customer satisfaction and streamline supplier relationships

ACCREDIA calibration certificate

An ACCREDIA calibration certificate is an official document exclusively issued by a metrological laboratory accredited by ACCREDIA. Widely recognized in Italy and throughout European countries adhering to the EA (European Cooperation for Accreditation), this certificate attests that an instrument has undergone calibration procedures endorsed by leading competent institutes.

Holders of ACCREDIA certificates are relieved of the obligation to prove to third parties that calibrations adhere to standards outlined in the quality system standard for metrological laboratories (UNI CEI EN ISO/IEC 17025), and are conducted according to ACCREDIA-approved procedures. Instruments and reference samples certified by ACCREDIA-accredited laboratories often serve as “primary reference standards” (e.g., gauge blocks) for calibrating and maintaining the accuracy of other equipment.

Calibration report with reference to national acknowledged standards (RDT) (UNI EN ISO 10012)

A laboratory test report referencing national acknowledged samples (UNI EN ISO 10012) is a document provided by metrological laboratories. It verifies that a test has been conducted with reference to nationally recognized samples, without requiring accreditation from the governing institution. Typically, these reports are necessary for executing internal inspections on measuring equipment used for field measurements, including pressure switches, multimeters, temperature meters, pressure gauges, calipers, dial indicators, micrometers, and more.

The credibility of these reports relies on the laboratory’s qualifications, the expertise of the operator, and the metrological procedures employed. Customers have the right to verify these features through on-site inspections.

Calibration questions and answers

Why calibrate instruments?

The calibration of measuring instruments is essential for compliance with UNI EN ISO 9001, particularly in section 7.6, which focuses on the management of measuring equipment.

The first section of paragraph 7.6 of UNI EN ISO 9001 outlines that “The organization shall determine the monitoring and measurement activities to be performed, as well as the monitoring and measuring equipment necessary to provide evidence of product conformity to the specified requirements.” As a result, the company must identify the equipment required for various stages of product realization and subject it to specific calibration intervals at a laboratory.

This includes not only tools needed for inspections and testing but also those used throughout the product life cycle, including design. Internally, the company must maintain an instrument log detailing each instrument’s identifying information and the maximum permissible errors for each metrological characteristic to be checked. This helps validate the accuracy of the instrument.

The second section of paragraph 7.6 of UNI EN ISO 9001 stipulates that “The organization has to establish processes to ensure that monitoring and measurement can be, and are, carried out in line with monitoring and measurement requirements.”

This means that processes must be in place to ensure that measurements adhere to the requirements for these activities, as detailed in UNI EN ISO 10012: “Measuring Management Systems – Requirements for Processes and measuring equipment.”

What does it mean to calibrate an instrument?

Calibration aims to identify the metrological characteristics of a measuring instrument, essentially providing a “snapshot” of its current state. It involves comparing the instrument with a reference sample and does not involve adjusting the instrument.

The purpose of calibration is to verify accuracy (error), which is the difference between the value detected by the instrument and the known value of the reference sample. This is why it’s often referred to as “with reference to acknowledged samples.” It’s important not to confuse calibration with adjustment: calibration defines the metrological characteristics of an instrument, while adjustment aims to enhance its accuracy by modifying its performance.

When an adjustment is necessary and possible, the sequence of steps typically involves initial calibration, adjustment, and then final calibration. Adjustments are usually excluded from calibration services and must be specifically requested by the customer and priced separately.

How often do I need to calibrate an instrument?

There are no set rules that dictate how often measuring instruments should be calibrated. Recommendations for calibration frequency can be provided once a consistent metrological confirmation system is in place. The intervals should be chosen based on various factors to ensure the instrument remains within its specified accuracy.

Factors to consider when determining calibration intervals include:

Manufacturer recommendations
How frequently the instrument is used
The type of instrument and how it wears over time due to use and storage conditions, including any observed drift
Operating and environmental conditions like temperature, humidity, and vibration
Desired measurement accuracy
Applicable technical and internal standards
Whether the instrument shows errors or uncertainties beyond acceptable limits
Incidents like shocks, falls, mechanical or electrical disturbances, adjustments, maintenance, improper use, and storage conditions.

For further details, refer to the reference standard guideline ILAC G24 – 2022.

What is metrological confirmation?

The UNI EN ISO 10012 standard focuses on metrological validation, defining it as follows: “Set of operations required to ensure that a measuring equipment complies with the intended use requirements.” Therefore, the aim of metrological validation is to manage the risk of incorrect results that measuring instruments and measuring processes could give and consequently affect the product quality.

Model of measuring system management

METROLOGICAL VALIDATION PROCESS

By analysing the UNI EN ISO 10012 3.5 standard, we can find the following aspects:

Note 1: it specifies that metrological validation refers to any process involved in ensuring the conformity of measuring instruments and includes calibration, verification, adjustment or repair and subsequent calibration; comparison with metrological requirements for intended use, sealing and labelling required.

Note 2: metrological validation process is not complete unless the suitability of measuring instrument is demonstrated and recorded for the intended use requirements; such activities represent “metrological validation” or improperly defined “metrological confirmation”.

Note 3: it specifies that the requirements for intended use include metrological characteristics, such as resolution, measuring range and maximum permissible errors.

Note 4: metrological requirements of measuring instrument used for that process must be different from product requirements; actually, metrological requirements must be more restrictive than the latter ones, to ensure that the instrument is suitable for verifying compliance of the product.

What is meant by measurement uncertainty?

According to the “International Vocabulary of Metrology” (VIM), measurement uncertainty is a “non-negative parameter that characterizes a range of values attributed to a measurand”. We have not to confuse the error with measurement uncertainty; the error is defined as the difference between a single test result and the known value of the measurand, the measurement uncertainty is, on the contrary, an estimate formed by several sources, each of which is called the “component of uncertainty” and it has the form of an interval. We usually use the expanded uncertainty U that is U = K*u, where K is the coverage factor 2 which gives a level of confidence of approximately 95%, as prescribed by EA (European Accreditation). The coverage factor K must always be indicated in the laboratory test report, so that it can be traced to the composite type uncertainty of the measured quantity.

The factors that affect measurement uncertainty can be summarized as follows:

Measuring instrument
Environmental conditions
The user
Measurement method
The measurand

Metrological characteristics of measuring instruments:

To know metrological characteristics of instruments is essential for a company, for a correct choice of the equipment required for product measurement requirements. Metrological characteristics have an immediate influence on product measurement; they are essential for checking the instrument errors and for a correct estimation of measurement uncertainty balance.

The main metrological characteristics are:

Unit of format
Resolution, repeatability, reproducibility, precision
Linearity
Hysteresis
Stability

The errors attributable to these characteristics contribute to the estimation of measurement uncertainty.

What does the verification of metrological requirements consist of?

Measuring instruments are used to verify that products features fall within the tolerances prescribed by the technical specifications of the products themselves. According to UNI EN ISO 14253-1, the product is compliant if the measured value falls within an area obtained by reducing the area of measurement uncertainty. The metrological validation, which is made after the calibration, compares the calibration results, which are the instrument errors, with the user-defined maximum permissible errors (MPEs) and a safe compliance zone can be determined.

What are the metrological characteristics of measuring instruments?

Unit of format:

The unit of format for analog instruments is the smallest division on the scale, while for digital instruments is the least increasing of significant digit. The unit of format is crucial to the introduction of another metrological feature, that is the resolution.

Resolution:

The resolution of an instrument is the smallest valid variation, to which a certain value can be attributed. It follows from the definition that, in the case of digital instruments, the resolution coincides with unit of format, while in analog instruments the resolution can be better than unit of format. It depends on the user’s reading capacity and the error that he can commit, so-called error of “parallax”.

Repeatability, reproducibility, precision:

The repeatability is the attitude of an instrument to provide reading values a little different between them, in consecutive readings on the same measurand, by unified procedure by the same operator, under the same conditions as influence quantities. We talk about reproducibility if these measurements are made on the same sample, but changing one or more conditions such as different locations, operators, measurement methods, measurement times and different measuring instruments. Therefore, reproducibility is more related to measurement method than the repeatability, which takes into account the single instrument and the user performing the measurement.

VIM combines the concept of repeatability and reproducibility with “measurement accuracy” defined as: “degree of concordance between indications or measured values obtained from a number of repeated measurements of the same object or similar objects, performed under specified conditions.” If specified conditions are those of repeatability, then precision becomes repeatability, but if conditions are those of reproducibility, then precision becomes reproducibility.

Measurement error (indicated in Laboratory Test report):

The measurement error is very important for a laboratory test report, the VIM defines the measurement error as “measured value of a quantity minus a reference value of the quantity”, therefore is the difference between the measured value and the measured value of standard sample (indicated on primary certificate). This difference is detected by instrument calibration and reported on laboratory test report.

The measurement error is not a contribution in evaluating the measurement uncertainty.

What is meant by linearity?

Linearity means how much the calibration curve deviates from the straight reference trend. Linearity calculates the absolute maximum error in the whole measuring range; in this case, it is called “integral linearity error”. In the case of instruments used for comparison, so that they can be reset to a point on the instrument measuring range, it is more useful to evaluate the “differential linearity” as the ratio between the variation of the instrument’s indication and the variation of the reference sample used for comparison (see graph below).

What is meant by hysteresis?

The hysteresis is the feature of the instrument toprovide different reading values at the same measurand when it varies for increasing values and decreasing values. Hysteresis is therefore an essential feature for instruments that can measure both increasing and decreasing values, such as dial indicators, pressure gauges, force gauges and so on. If a measuring instrument is subject to hysteresis, but its use is only for increasing or decreasing values, the maximum error evaluation can exclude hysteresis and thus is not used to estimate the measurement uncertainty. (see chart below).

What is stability?

The stability is the attitude of an instrument to provide readings a little different between them, in readings independently performed on the same measurand within a defined time interval, with a unified process and under the same conditions for influence quantities. The stability of a measuring instrument is essentially the ability to maintain its metrological characteristics over time. Stability is also called “drift”; in fact, the instrument drift is defined as the time variation of an indication, due to variations in metrological properties of a measuring instrument. Therefore, stability can be obtained by comparing two calibration curves performed at different times but made under the same conditions. (see chart below).

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Calibration Services

Dimensional

Dimensional

Environmental

Environmental

Force

Force

Torque

Torque

Hardness

Hardness

Pressure

Pressure

Defects

Defects

Electrical

Electrical

Mass

Mass

Coating

Coating

Differences Between Laboratory Test Reports and ACCREDIA Calibration Certificates

ACCREDIA calibration certificate

Calibration report with reference to national acknowledged standards (RDT) (UNI EN ISO 10012)

Calibration questions and answers

Do you need to calibrate your instruments?

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