Review of quality qualification: In - depth analysis of the main differences between calibration and verification
In the actual scenario of quality certification audits, there is a relatively common and serious problem. Some auditors often put forward some unreasonable requirements deviating from the standards to the audited parties when performing audit tasks. One of the most obvious manifestations is that they cannot accurately distinguish between the two important concepts of calibration and verification. In China, according to the actual production needs and relevant regulations of legal metrology management, the measurement devices of many organizations can meet the actual use requirements through calibration. However, some auditors ignore these regulations. During the audit, once they find that the measurement devices of an organization have not been verified, they will issue a non - conformity report stating no verification. Moreover, they will force the organization to implement control in accordance with the verification process and even require the organization to send the measurement devices to a professional metrology department for verification. This inappropriate practice has brought relatively large economic losses to the organization and increased the unnecessary cost burden on the organization.
Explanation of the definitions of calibration and verification
Definition of calibration
The standard ISO10012 - 1 "Quality assurance requirements for measurement and test equipment" gives a clear definition of "calibration": "A set of operations under specified conditions to determine the relationship between the value indicated by a measuring instrument or a measuring system or the value represented by a material measure or a reference material and the corresponding known value of the measurand." Regarding this definition, we have the following detailed explanations:
1. Evaluation of indication error: The calibration results can be used to evaluate the indication errors of measuring instruments, measurement systems, or physical measuring tools. By comparing with the known standard values, the deviation between the indication value of the measuring device and the true value can be clearly understood. At the same time, calibration can also assign values to the marks on any scale, making the measurement results more accurate and reliable.
2. Determine other metrological characteristics: In addition to evaluating the indication error, calibration can also be used to determine other metrological characteristics. These characteristics are of great significance for the performance evaluation and actual use of measuring devices.
3. Calibration result recording: The results of calibration are usually recorded in specific documents, which are sometimes referred to as calibration certificates or calibration reports. These records detail the calibration process and results and are important proofs of the accuracy of the measuring device.
4. Representation forms of calibration results: Calibration results can be presented in various forms, such as correction values, calibration factors, or calibration curves. These representation forms can provide specific guidance for subsequent measurement operations and help operators perform measurements more accurately.
Definition of verification
1. Connection with measurement instrument management: The main purpose of verification is to check the deviation between the indicated value of a measurement instrument and the corresponding known quantity value. Through this check, it is ensured that the indication error of the measurement instrument is always less than the maximum permissible error specified in the relevant standards, regulations, or specifications for measurement instrument management. This is an important measure to ensure the accuracy and reliability of measurement instruments.
2. Determination of the status of measuring instruments: Based on the results of the verification, a series of decisions need to be made regarding the measuring instruments, such as continued use, investigation, repair, use at a lower level, or declaration of scrapping. In any case, when the verification is completed, the details of the verification should be recorded in the dedicated record of the measuring instrument to facilitate the tracking and management of the status of the measuring instrument. The definition of verification given by the international metrology organization is: "The procedure for ascertaining and confirming whether a measuring instrument meets the statutory requirements, which includes inspection, marking, and/or issuing a verification certificate."
Discussion on the essential differences between calibration and verification
It can be clearly seen from the above definitions that there are essential differences between calibration and verification. The two cannot be confused with each other, and even less can they be regarded as the same. Now let's discuss in detail the main differences between them.
The purposes are different
Purpose of calibration
The core purpose of calibration is to evaluate the indication error of the measuring device against the measurement standard, so as to ensure the accuracy of the measured value. This is a bottom - up process of value traceability. By comparing with a higher - level measurement standard, the indication error of the measuring device is determined. The evaluation of this indication error needs to be regulated according to the calibration procedures formulated by the organization. Calibration should be carried out according to the specified calibration cycle, and detailed calibration records and calibration marks should be made. The function of calibration is not only to evaluate the indication error of the measuring device and determine relevant metrological characteristics. The calibration results can also be presented in the form of correction values or calibration factors, providing specific guidance for the operation of the measurement process. For example, in a machining organization, after calibrating the calipers they use, it is found that compared with the measurement standard, the indicated value is 0.2mm larger. At this time, this 0.2mm data can be used as a correction value, clearly indicating in the calibration mark and record that the calibrated value is 0.2mm larger than that of the standard device. In the subsequent process of using this caliper to measure a physical object, the operator only needs to subtract this 0.2mm correction value from the measured value to obtain the accurate actual measured value of the physical object. As long as the purpose of value traceability can be achieved and the indication error of the measuring instrument is clearly known, the purpose of calibration is achieved.
Purpose of verification
The purpose of verification is to conduct a mandatory and comprehensive assessment of the measuring device. This falls within the scope of measurement value unification and is a top - down measurement value transfer process. Verification requires assessing whether the measuring instrument meets the specified requirements, and these specified requirements are the error ranges stipulated in the verification regulations for the measuring device. Through the verification process, it can be accurately determined whether the error range of the measuring device is within the specified error range. Only when the error range of the measuring device is within the specified range can the measuring device be considered to meet the requirements and can continue to be used; if it exceeds the specified range, corresponding treatment needs to be carried out according to the specific situation.