# What Is Calibration And Why Is It Important Pdf

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Here, we are talking about metrological calibration in the world of measurement technology.

Measurement consists of comparison of samples of unknown composition with standards of known composition or with scales calibrated with respect to such standards. The standards used must simulate the unknowns with respect to matrix and level of analyte if the comparisons are to be valid. This paper reviews the fundamental aspects of calibration, describes various approaches that may be utilized, and considers the sources of error in the calibration process. The evaluation of calibration uncertainty and ways to minimize it are discussed.

## What is Calibration and Why is it so Important?

Here, we are talking about metrological calibration in the world of measurement technology. Formally, calibration is the documented comparison of the measurement device to be calibrated against a traceable reference device. The reference device should be also calibrated traceably, more on that later on. With some quantities the reference is not always a device, but can also be for example a mass, mechanical part, physical reference, reference liquid or gas.

When you make a calibration and compare two devices, you may find out there is some difference between the two. So, it is pretty logical that you may want to adjust the device under test to measure correctly. This process is often called adjustment or trimming. Formally, calibration does not include adjustment, but is a separate process. In everyday language the word calibration sometimes also includes possible adjustment. But as mentioned, the adjustment is a separate process according to most formal sources.

The SI system is the international system of units, that specifies the basic units used in measurement science. SI system determinates 7 base units meter, kilogram, second, ampere, kelvin, mole and candela and 22 derived units. The base units are derived from constants of nature. This document is typically called a Calibration Certificate.

A calibration certificate includes the result of the comparison and all other relevant information of the calibration, such as equipment used, environmental conditions, signatories, date of calibration, certificate number, uncertainty of the calibration, etc. It was mentioned that the reference standard that is used in calibration must be traceable. This traceability means that the reference standard must have also been calibrated using an even higher-level standard.

The traceability should be an unbroken chain of calibrations, so that the highest-level calibration has been done in a National calibration center, or equivalent. So, for example, you may calibrate your process measurement instrument with a portable process calibrator.

The portable process calibrator you used, should have been calibrated using a more accurate reference calibrator. The reference calibrator should be calibrated with an even higher-level standard or sent out to an accredited or national calibration center for calibration. The national calibration centers will make sure that the traceability in that country is at the proper level, using the International Calibration Laboratories or International comparisons.

If the traceability chain is broken at any point, any measurement below that cannot be considered reliable. Metrological Traceability in Calibration — Are you traceable?

When you calibrate an instrument with the higher-level device, the process always includes some uncertainty. Uncertainty can be caused by various sources, such as the device under test, the reference standard, calibration method or environmental conditions. In the worst case, if the uncertainty of the calibration process is larger than the accuracy or tolerance level of the device under calibration, then calibration does not make much sense.

The aim is that the total uncertainty of calibration should be small enough compared to the tolerance limit of the device under calibration. The total uncertainty of the calibration should always be documented in the calibration certificate. Calibration uncertainty for dummies. The ratio is the accuracy or uncertainty of the device under test compared to the one of the reference standard. We commonly hear about using a TAR ratio of 4 to 1, which means that the reference standard is 4 times more accurate than the device under test DUT.

It is good to remember that for example the TAR only takes into account the accuracy specifications of the instruments and does not include all the uncertainty components of the calibration process. Depending on the type of calibration, sometimes these uncertainty components can be larger than the accuracy specifications.

Most often when you calibrate an instrument, there is a tolerance limit acceptance limit set in advance for the calibration. This is the maximum permitted error for the calibration. In the case of a failed calibration, you should take corrective actions to make the calibration pass. Typically, you will adjust the DUT until it is accurate enough. Calibration Out of Tolerance: What does it mean and what to do next? At this point, you may wonder why should you calibrate something, or what are the reasons for calibrating?

In industrial process conditions, there are various reason for calibration. Examples of the most common reasons are:. Why calibrate? There is no one correct answer to this question, as it depends on many factors.

Some of the things you should consider when setting the calibration interval are, but not limited to:. For more detailed discussions on how often instruments should be calibrated, please read the below linked blog post:. How often should instruments be calibrated? In a process plant, the control system controls the plant.

The control system obtains measurement data from the various measurements in the plant and controls the plant based on the measurement data. So, if the measurement data is incorrect, the controlling of the plant will also be incorrect. A calibration laboratory accreditation is a third-party recognition of the competence of the laboratory. The Beamex Oy calibration laboratory at the headquarters in Finland has been accredited since Traditionally calibration has been performed using a calibration reference and writing the results manually on a piece of paper.

In a modern electronic and paperless system everything can be done paperless. The planning can be done in the maintenance management system, from where the work orders are electronically transferred to the calibration management system. The calibration management system can download the work orders electronically to portable documenting calibrators. When the work is performed with documenting calibrators, they automatically save the results into their memory. Once calibration work is completed, the results can be downloaded from calibrator to the calibration management software.

Finally, the calibration software sends an acknowledgement to the maintenance management system that the work has been completed. Process instrument calibration is comparing and documenting the measurement of a device to a traceable reference standard.

It is important to calibrate so that you can be confident that your measurements are valid. Measurement validity is important for many reasons, including safety and quality.

For best results and reliability, make sure the uncertainty of the calibration is small enough. Or use a calibrator that has accuracy specification several times better than the device under test. Finally, setting calibration tolerances and frequency should be determined by several factors, including instrument criticality. The reference standard should also be calibrated traceably. Formally the calibration does not include adjustment or trimming, although in everyday language it is often included.

See more at What is calibration. Formally, traceability is a property of the result of a measurement, through an unbroken chain of comparisons each having stated uncertainties. In practice, traceability means that the reference standard has also been calibrated using an even higher-level standard. The traceability should be an unbroken chain of calibrations so that the highest-level calibration has been done in a National calibration center or equivalent.

The portable process calibrator you used, should be calibrated using a more accurate reference calibrator. Calibration uncertainty is a property of a measurement result that defines the range of probable values of the measurand. In a calibration procedure, the test accuracy ratio TAR is the ratio of the accuracy tolerance of the unit under calibration to the accuracy tolerance of the calibration standard used.

In a calibration procedure, the test uncertainty ratio TUR is the ratio of the accuracy tolerance of the unit under calibration to the uncertainty of the calibration standard used.

In industrial process conditions, there is various reason for calibration. A calibration certificate includes the result of the comparison and all other relevant information of the calibration, such as equipment used, environmental conditions, signatories, date of calibration, certificate number, the uncertainty of the calibration, etc. What is calibration? What does metrological calibration mean?

Adjustment When you make a calibration and compare two devices, you may find out there is some difference between the two. Traceability It was mentioned that the reference standard that is used in calibration must be traceable.

More information on the metrological traceability can be found in the below blog post: Metrological Traceability in Calibration — Are you traceable? Calibration uncertainty, measurement uncertainty When you calibrate an instrument with the higher-level device, the process always includes some uncertainty. More information on calibration uncertainty can be found in this blog post: Calibration uncertainty for dummies.

It is recommended to always calculate the total uncertainty of the calibration. More detailed information on the calibration uncertainty, please read the related blog post: Calibration uncertainty for dummies. More detailed discussions on calibration tolerance can be found in the below blog post: Calibration Out of Tolerance: What does it mean and what to do next?

Why should you calibrate? How often you should calibrate? Another common related discussion is how often should instruments be calibrated? Accredited calibration labs A calibration laboratory accreditation is a third-party recognition of the competence of the laboratory.

Going digital — paperless calibration Traditionally calibration has been performed using a calibration reference and writing the results manually on a piece of paper.

How to calibrate pressure transmitters. How to calibrate weighing scales. How to calibrate temperature transmitters. Conclusions Process instrument calibration is comparing and documenting the measurement of a device to a traceable reference standard. Stay updated with new articles! We are constantly writing new calibration related educational articles in our blog. Please visit our blog for updates and subscribe for notifications: Visit Beamex Blog.

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characteristics that influence the measurement uncertainty for the intended use (​see ISO ). Why Are Calibrations Necessary? There.

## Calibration

In measurement technology and metrology , calibration is the comparison of measurement values delivered by a device under test with those of a calibration standard of known accuracy. Strictly speaking, the term "calibration" means just the act of comparison and does not include any subsequent adjustment. The formal definition of calibration by the International Bureau of Weights and Measures BIPM is the following: "Operation that, under specified conditions, in a first step, establishes a relation between the quantity values with measurement uncertainties provided by measurement standards and corresponding indications with associated measurement uncertainties of the calibrated instrument or secondary standard and, in a second step, uses this information to establish a relation for obtaining a measurement result from an indication.

There are three main reasons for having instruments calibrated: 1 To ensure readings from an instrument are consistent with other measurements. Is calibration required? Yes: Demonstrable control of measurement and test equipment is required. Part of this is ensuring that instruments are calibrated on a rational periodic cycle, and that records are maintained and reviewed.

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