In the world of metrology, verification and calibration play a crucial role. These processes ensure that measuring instruments provide reliable and accurate results. Understanding these procedures is essential for companies and research institutions that depend on precise measurements. The following article highlights the different aspects of verification and calibration and explains why they are essential for ensuring accurate measurements.
Difference between verification and calibration
Verification and calibration are two fundamental processes in metrology that are often confused. Both serve to ensure accurate measurements, but they differ in their objectives and legal frameworks.
Definition and purpose of verification
Verification is a legally prescribed process that is mandatory for certain measuring instruments. It serves to protect consumers and ensure fair trading conditions. During verification, a measuring instrument is checked to ensure that it meets the legal requirements. This applies in particular to devices used in commercial or official transactions, such as scales in retail stores or fuel dispensers at gas stations. In addition to the technical inspection, the calibration process also includes the marking of the device with a calibration mark. This confirms conformity with the legal requirements. The calibration must be repeated at specified intervals to ensure long-term compliance with the regulations. Only state-approved bodies may carry out calibrations. The legal framework for calibrations in Germany is regulated by the Measurement and Calibration Act and the Measurement and Calibration Ordinance.
Definition and purpose of calibration
In contrast to verification, calibration is a voluntary process that is, however, indispensable for many companies and research institutions. During calibration, a measuring instrument is compared with a reference standard. The aim is to determine and document the deviation of the measuring instrument from the true value. This process is particularly important in industry and research and development. It ensures the traceability of measurements to national or international standards. Calibration provides important information about the measurement accuracy and precision of a device. It enables users to quantify measurement uncertainty and make corrections as needed. Unlike verification, there are no legally prescribed intervals for calibration. The frequency of calibration depends on the requirements of quality management and the specific application. Calibrations can be carried out by accredited laboratories such as the ZERA DAkkS calibration laboratory.
The calibration process in detail
The calibration process is a complex procedure that requires the utmost precision and care. It comprises several steps, from preparation to actual execution, and includes the documentation and evaluation of the results.
Preparation for calibration
Thorough preparation is crucial for a successful calibration. First, the measuring instrument to be calibrated is identified and its technical specifications are checked. The environmental conditions in the calibration laboratory must meet the requirements and be kept constant. Temperature, humidity and other relevant parameters are continuously monitored. Before the actual calibration, the measuring instrument undergoes a functional test. Any contamination or damage is eliminated. The selection of suitable reference standards is based on the specifications of the device to be calibrated. These standards themselves must be regularly calibrated and traceable to national or international standards. A detailed calibration plan is created that defines the points to be measured, the number of repetitions and the order of the measurements. All the tools and documentation needed for the calibration are prepared.
Performing the calibration
The actual calibration process follows the previously created plan. The measuring instrument to be calibrated is compared with the reference standard. Measurements are taken at various points across the entire measuring range of the device. The number of measuring points depends on the type of device and the calibration requirements. Each measuring point is measured multiple times to capture random deviations. During calibration, all relevant data is carefully recorded. This includes the measurement values themselves, but also environmental conditions and any special features. For electrical measuring instruments, such as those calibrated in the ZERA DAkkS calibration laboratory, this includes measurements of voltage, current, power and other electrical quantities. The calibration is carried out under strictly controlled conditions to minimize interference. Particular attention is paid to observing the prescribed waiting times between measurements to take thermal effects into account.
Documentation and evaluation of the calibration results
Once the measurements are complete, the careful evaluation of the collected data begins. The measured values are compared with the nominal values to determine deviations. Statistical methods are used to calculate the measurement uncertainty. This indicates the range within which the true value lies with a certain probability. The results are recorded in a detailed calibration certificate. This contains information about the calibrated device, the reference standards used, the ambient conditions and the measured values determined, including uncertainties. In addition, traceability to national or international standards is documented. In the case of DAkkS calibration, as carried out in the ZERA laboratory, there is a direct traceability to the German Federal Institute of Physics and Metrology (PTB). The calibration certificate serves as proof of the accuracy of the measuring device and is often part of the quality management system. Finally, the results are analyzed to identify any trends or anomalies.
The importance of accredited calibration laboratories
Accredited calibration laboratories such as the ZERA DAkkS calibration laboratory play a central role in ensuring precise and reliable measurements. They offer a high standard of quality and are recognized both nationally and internationally.
The advantages of accreditation
Accrediting a calibration laboratory brings with it numerous advantages. First of all, it ensures a high quality of the calibrations carried out. Accredited laboratories must meet strict requirements in terms of their technical expertise, impartiality and reliability. This creates trust in the accuracy and traceability of the measurement results. Customers benefit from the certainty that their measuring instruments are being calibrated according to internationally recognized standards. Accreditation also facilitates the recognition of calibration results across national borders. This is particularly important for companies that operate internationally or export products. Accredited laboratories such as ZERA are subject to regular inspections by the German accreditation body (DAkkS). These audits ensure that the high standards are continuously met. Another advantage is the traceability of measurements to national and international standards. This ensures the comparability of measurement results worldwide.
The accreditation process
The path to accreditation of a calibration laboratory is complex and demanding. First, the laboratory must implement a comprehensive quality management system according to the standard DIN EN ISO/IEC 17025. This standard specifies the general requirements for the competence of testing and calibration laboratories. The actual accreditation process begins with an application to the DAkkS. This is followed by a detailed document review, in which the laboratory must demonstrate that it meets all normative requirements. Subsequently, a team of auditors carries out an on-site assessment. During this process, the technical facilities, procedures and the competence of the personnel are thoroughly examined. Any deviations must be remedied by the laboratory. After a successful assessment, the laboratory receives the accreditation certificate. However, accreditation is not a one-time process. ZERA and other accredited laboratories must undergo regular monitoring audits and repeat assessments. This ensures that the high standards are maintained permanently and that the laboratory keeps pace with technological developments.
Calibration of various measured variables
Calibration covers a wide range of measured variables, particularly in the field of electrical metrology. Each measured variable requires specific procedures and expertise.
Direct current and low frequency
Calibration of DC and low frequency is an important basis in electrical metrology. DC calibration involves the precise measurement of constant electrical currents. Calibration is performed by comparison with highly accurate reference sources. Various current levels are tested across the entire measuring range of the device under test. Low frequency measurements involve alternating currents and voltages in the range of a few hertz to a few kilohertz. Here, the precise determination of amplitude and frequency is crucial. The calibration also takes into account factors such as ripple and distortion of the signal. In the ZERA DAkkS calibration laboratory, high-precision calibrators and reference measuring instruments are used for these measurements. Traceability to the national standards of the PTB is always guaranteed. Calibration in this area is particularly important for applications in power engineering, electronics and industrial control technology.
Voltage and current measurements
The calibration of voltage and current measuring instruments is of fundamental importance for many areas of electrical engineering and electronics. For voltage measurements, the spectrum ranges from microvolts to kilovolts. Calibration is performed by comparison with highly stable reference voltage sources. Particular attention is paid to linearity over the entire measuring range and to frequency dependence in the case of alternating voltages. Current measurements require similar care, with thermal effects also needing to be taken into account. The ZERA DAkkS calibration laboratory uses precise multimeters and current transformers for these calibrations. The measurement uncertainty is carefully determined and documented for each measurement point. These calibrations are essential for quality assurance in electronics manufacturing, for testing laboratories and in energy distribution. They ensure that electrical devices work safely and efficiently and that energy measurements are carried out correctly.
Power and energy measurements
The calibration of power and energy measuring instruments is becoming increasingly important as renewable energies expand and energy efficiency grows in significance. When measuring power, the accuracy of the devices is checked at different power factors and frequencies. This is particularly important for the precise measurement of active power, reactive power and apparent power. The calibration of energy measuring instruments also includes testing long-term stability and correct integration over time. The ZERA laboratory uses high-precision power analyzers and energy meter test systems for this purpose. The calibration also takes into account modern scenarios such as measurement in the case of non-sinusoidal currents, as they occur in switching power supplies or in renewable energy sources. These calibrations are indispensable for energy suppliers, grid operators and manufacturers of energy measuring instruments. They ensure that energy can be billed correctly and that efficiency measures can be evaluated accurately.
Other calibratable quantities
In addition to the main quantities mentioned, the ZERA DAkkS calibration laboratory offers calibrations for a variety of other electrical parameters. These include phase angle, frequency, resistance and capacitance. Phase angle calibration is particularly important for analyzing AC power systems and assessing power quality. Frequency measurements are carried out with the highest precision, which is important for telecommunications and time standards. The calibration of resistors and capacitors is essential for the characterization of electronic components. Special measured variables such as voltage and current ratios, which play a role in transformers and instrument transformers, are also calibrated. Specific calibration procedures and reference standards are used for each of these variables. The wide range of sizes that can be calibrated highlights the laboratory’s extensive expertise and allows customers to have all their relevant electrical measuring devices calibrated in one place.
The professional calibration process at ZERA
The calibration process at ZERA follows a strict procedure that ensures maximum precision and reliability. Each step is carefully planned and documented.
Pre-calibration and adjustment
The first step in the ZERA calibration process is pre-calibration and adjustment. This begins with a thorough inspection of the device to be calibrated. Technicians check the device for external damage or signs of wear that could affect the measurement results. This is followed by a functional test to ensure that all components are working properly. The actual pre-calibration serves to record the current state of the device. This is where the ZERA standard load points come into play – predefined measuring points that allow a comprehensive assessment of the device’s accuracy. Based on these results, an adjustment is carried out if necessary. This fine adjustment ensures that the device works within the tolerances specified by the manufacturer. The pre-calibration and adjustment are crucial to create the best conditions for the subsequent accredited calibration.
DAkkS calibration
After pre-calibration and any necessary adjustment, the actual DAkkS calibration takes place. This process is subject to strict quality standards and is carried out by specially trained technicians. The calibration is carried out under precisely controlled environmental conditions to minimize influences such as temperature, humidity and electromagnetic interference. The device to be calibrated is compared with highly precise reference standards, which themselves are regularly traced back to national standards. The measurements are carried out at the ZERA standard load points, supplemented by additional measuring points that are relevant for the specific application of the device. Each measuring point is measured multiple times to detect random deviations and to determine the measurement uncertainty precisely. Throughout the entire calibration, all relevant data is carefully documented. This includes not only the measured values themselves, but also information on the standards used, the ambient conditions and any special features during the calibration process.
Traceability to national standards
A central aspect of DAkkS calibration at ZERA is ensuring traceability to national standards. This means that every measurement can ultimately be traced back to the primary standards of the Physikalisch-Technische Bundesanstalt (PTB). This traceability is ensured by an unbroken chain of comparative measurements. The reference standards used in the ZERA laboratory are regularly compared with higher-order standards, which in turn are directly traceable to the PTB standards. This process ensures that calibrations performed at ZERA are internationally recognized and comparable. Traceability is documented in detail in the calibration certificate. It includes information on the reference standards used, their calibration certificates, and the uncertainty budgets of the measurements. This complete documentation enables customers to prove the quality and accuracy of their measuring instruments at any time. Traceability is especially important for companies that operate in regulated industries or need to meet international quality standards.
Differences between factory and DAkkS calibration
Factory and DAkkS calibrations are two different approaches to verifying and documenting the measurement accuracy of devices. Both have their specific advantages and disadvantages, as well as areas of application.
Factory calibration: advantages and applications
Factory calibration is a calibration process carried out by the manufacturer or a non-accredited laboratory. It offers several advantages: First of all, it is usually cheaper and faster to carry out than a DAkkS calibration. This makes them attractive for applications where no legal or contractual requirements demand an accredited calibration. Factory calibrations are often tailored to the specific properties and applications of the device. Manufacturers can use their intimate knowledge of the device to check particularly relevant measurement points. Another advantage is flexibility: factory calibrations can be more easily adapted to customer-specific requirements. They are particularly suitable for internal quality control, research and development, and for applications where absolute traceability to national standards is less critical. Many companies use factory calibrations for routine checks between accredited calibrations to continuously monitor the performance of their equipment.
DAkkS calibration: advantages and applications
DAkkS calibration, carried out by accredited laboratories such as ZERA, offers the highest level of reliability and recognition. Its main advantage lies in the guaranteed traceability to national and international standards. This creates confidence in the measurement results and enables comparability of measurements worldwide. DAkkS calibrations are subject to strict quality controls and regular reviews by the German accreditation body. This ensures consistently high standards and technical competence. The issued calibration certificates are internationally recognized, which is particularly important for companies involved in global trade. DAkkS calibrations are indispensable in regulated areas such as medical technology, the automotive industry or aerospace. They are also required when measuring instruments play a role in legal matters or in official inspections. For companies with ISO 9001 certification or similar quality management systems, DAkkS calibrations are often mandatory. Despite higher costs and longer lead times, they offer long-term advantages by minimizing measurement risks and increasing product quality.
The importance of regular calibration for measurement accuracy
Regular calibrations are crucial to ensure the long-term accuracy and reliability of measuring instruments. They play a key role in quality assurance and process optimization.
Factors that influence measurement accuracy
The measurement accuracy of devices can be influenced by various factors. Aging of components often leads to gradual changes in measurement properties. Mechanical stresses, temperature fluctuations and vibrations can affect calibration. Electromagnetic interference and humidity also play a role. Electronic devices can suffer from drift effects, which cause a gradual shift in the measured values. The intensity of use and the ambient conditions at the place of use also influence long-term stability. Even minor deviations can have significant effects in critical applications. Regular calibrations help to identify and compensate for these influences. They make it possible to identify trends in device performance at an early stage and take preventive action. By analyzing calibration data over extended periods of time, companies can better assess the reliability of their measuring instruments and define optimal calibration intervals.
Recommended calibration intervals
Determining optimal calibration intervals is an important but often complex task. In general, the ideal interval depends on several factors: the type of measuring instrument, its frequency of use, the environmental conditions and the accuracy requirements of the specific application. For many standard devices, manufacturers and experts recommend annual calibrations. For especially critical applications or frequent use, shorter intervals of six months or less may be appropriate. On the other hand, rugged devices in stable environments may tolerate longer intervals. A proven method for determining optimal intervals is to analyze historical calibration data. If the data shows consistent stability, the intervals may be extended. If there are noticeable trends toward deviation, shorter intervals are advisable. Many companies implement a tiered system in which critical devices are calibrated more frequently than less critical ones. Periodic checks between calibrations, known as intermediate tests, can provide additional certainty. ZERA advises customers individually on determining suitable calibration intervals to find the optimal balance between measurement accuracy and cost-effectiveness.
Conclusion: the indispensable role of verification and calibration
Verification and calibration are fundamental processes that play an indispensable role in modern metrology. They are the backbone of reliable and precise measurements in almost all areas of science, industry and everyday life.
The importance of these processes can hardly be overestimated. In industrial manufacturing, they ensure the quality of products and the efficiency of production processes. In research, they enable trustworthy and reproducible results that drive scientific progress. In trade, they ensure fair transactions and protect consumer interests. In sensitive areas such as medical technology or aerospace, precise measurements can be life-saving.
Continuous technological development presents metrology with new challenges. At the same time, innovations such as quantum technologies and artificial intelligence are opening up fascinating possibilities for even more accurate and efficient measurements. In this dynamic environment, accredited laboratories such as the ZERA DAkkS calibration laboratory play a key role. Through their expertise and strict quality standards, they ensure the traceability and international comparability of measurements.
It is crucial for companies and organizations to recognize the importance of regular calibrations and to integrate them into their quality assurance processes. The choice between factory and DAkkS calibration should be carefully considered based on specific requirements and regulatory specifications.
Ultimately, verification and calibration are not just technical processes, but fundamental building blocks of trust in our increasingly technology-driven world. They ensure the reliability of the data on which important decisions in business, science and society are based. In an age when the precision and reliability of measurements are becoming ever more important, verification and calibration remain indispensable guarantors of progress and safety.