What Is the Difference Between Calibration, Adjustment, and Verification?
If you have worked with measuring instruments, you have probably come across such terms as calibration, adjustment, and verification. They all describe technical processes related to the functioning of measuring instruments. Yet, they are not synonyms. Understanding the differences between these terms is essential because they serve different purposes. Getting them mixed up might lead to faulty records, poor audit results, and even incorrect conclusions about the state of a measuring instrument. Let us first define each term and highlight the conditions under which they are applied and Instrument calibration
Calibration
Calibration is a process where a measuring instrument is compared to a reference instrument with a known accuracy. By doing this, it becomes possible to establish if the instrument under calibration provides accurate measurements and to what extent it deviates. Calibration is always accompanied by technical documentation that contains calibration results – calibration certificates. One should remember, however, that calibration, as a rule, does not affect the indications of an instrument. To put it another way, while calibration can reveal an error, it cannot correct it. Example A digital thermometer was calibrated at a temperature of 100 degrees Celsius. As a result of the calibration, it was found that the thermometer indicates 99.7 degrees Celsius at the calibration point. The instrument was therefore calibrated. Calibration determines the degree of measurement accuracy; it cannot change the characteristics of an instrument
Adjustment
The technical term adjustment refers to changing an instrument so that its indication coincides with the required value. An adjustment is made when an instrument is found to be inaccurate based on calibration. In other words, if calibration revealed deviations beyond the allowable limits, the instrument can be adjusted to make it more accurate. After the adjustment, calibration of an instrument is performed again to check if the adjustment has been done correctly. Example A pressure gauge in a compressed air station was found to indicate a pressure 3 kPa higher than the reference instrument. Such discrepancy goes against the permissible limits of error. The gauge was adjusted; after that, a calibration was performed to check if there were any errors left. An adjustment corrects measurement errors after they have been revealed.
Verification
Verification is a process of proving that a measuring instrument meets the requirements for its use. Verification differs from calibration in that verification does not always determine the amount of deviation of an instrument. While calibration answers the question of how accurate the instrument is, verification answers the question of whether the instrument is accurate enough. In other words, verification focuses on the comparison of an instrument with specific technical requirements, while calibration determines the degree of accuracy of an instrument. Example Before using a weighing scale in a laboratory, it is necessary to verify that it is accurate enough for the upcoming tests. The verification process will show that either the scale is accurate or not. Verification ensures that an instrument complies with the required technical specifications.
Comparison of the Three Concepts
The table below compares the three concepts in terms of their goals, impact on an instrument, and provision of measurement data. The Interrelation of the Three Processes Usually, processes described by these three terms are interrelated. First of all, an instrument is subjected to calibration to determine its accuracy. Then, based on the calibration results, an adjustment is performed if the calibration revealed deviations beyond the permissible limits. Finally, another calibration or verification is performed to ensure that the adjustment was performed correctly. By doing these three actions in sequence, it becomes possible to determine the accuracy of the instrument, eliminate errors if any, and ensure the accuracy of the adjustment.
The Need to Distinguish Between Them
Proper knowledge of the distinction between the three terms is essential for at least two reasons. First, using correct terms makes it easier to communicate with external parties such as customers, regulatory authorities, and auditors. Second, the correct application of terms ensures good auditing results. Knowing which action was taken and whether it was documented correctly allows one to provide more reliable evidence of the conformity of products during an audit. Moreover, understanding what action was taken allows one to evaluate the state of the measuring instrument more accurately. For example, if the instrument was calibrated, one can be sure that its characteristics were measured and documented. If the instrument was adjusted, one can assume that a calibration was performed beforehand and potential inaccuracies were eliminated. If the instrument was verified, one can conclude that it meets the required accuracy and therefore can be used with confidence. Common Myths About Calibration, Adjustment, and Verification Some myths about calibration, adjustment, and verification could be dispelled by examining the definitions and examples given above. Calibration corrects instrument characteristics This is not true because calibration only measures accuracy; it cannot change anything in an instrument. If calibration reveals errors, they must be eliminated by adjustment.
Verification is a replacement for calibration
Even though verification can be used to check if an instrument complies with requirements, it does not provide information about the extent of compliance. In other words, verification only tells you whether the instrument is accurate enough, but it does not tell you how accurate it is. Calibration, on the other hand, helps obtain quantitative characteristics of accuracy. Adjustment can be performed without calibration This is wrong because adjustment cannot be done without knowing the current characteristics of the instrument. Calibration provides this information.
When to Apply Calibration, Adjustment, and Verification Usually, calibration is performed periodically to determine how accurate the instrument is. Adjustment is performed only when an instrument is found to be inaccurate. Verification is performed more frequently, both before working with the instrument and after it has been transported or adjusted to determine whether it can be used.
Summary
Calibration, adjustment, and verification are three different processes, each of which plays its role in ensuring the accuracy of measurements. These terms are not interchangeable, but, together, they allow for controlling the accuracy of measuring instruments and, consequently, the quality of products. Calibration ensures that one knows the accuracy level of an instrument. Adjustment eliminates measurement errors if any. Verification ensures that an instrument can be used for further measurements with confidence. All three terms taken together allow one to determine both qualitative and quantitative characteristics of an instrument Calibration system
