Themetrologyis a field ofscience dedicated to measurement, defined as the process of comparing an unknown quantity, called a measured quantity, with a standard of a known quantity.
Metrology can be divided intothree different fields:scientific metrology, technical metrology and legal metrology.
Thescientific metrologyit involves the application of measurement standards for individual measurement quantities and the development of new measurement methods.
Thetechnical metrologyis related to the measurement of individual measured values, the development ofmeasurement toolsand measurement methods.
Thelegal metrologyis part of metrology, which is governed by regulations forensure accuracyand uniformity of measurements, especially in cases of potential conflicts of interest, or when inaccurate measurement results may have negative consequences for individuals or society.
Index
What is metrology?Basic concepts
These conceptsmetrology basicsThe fundamental objective of metrology is to guarantee traceability as a prerequisite for the comparison of measurement results.
The tasks of legal metrology are carried out by means ofcalibrationof measurement patterns and checking the accuracy of measuring instruments.
Checking the accuracy of measuring instruments consists of the following procedures:
Examination, verification and evaluation of the conformity of measuring instruments with specific metrological requirements and declarations.
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Typical analysis of measuring instrumentsin metrology
The standard control of measuring instruments is regulated by the Regulation on the standard control of measuring instruments (Official Gazette No. 93/96). The manufacturer or distributor of a measuring instrument is obliged to submit a request for type tests to the State Agency for Standardization and Metrology (DZNM) before the instrument is placed on the market.
If the type of instrument under examination meets the relevant metrological requirements, the State Office for Standardization and Metrology will issue the approval of that type of instrument.
Based on the approval of a measuring instrument, it may be manufactured, distributed or used in the field oflegal metrology.
will be granteda markapproval to an approved instrument meeting the applicable requirements (for example, non-automatic scale, accuracy class III) with an approval mark HR M-3-x, where x indicates the annual work number.
Measuring instruments with type approval identification marks may be manufactured, imported or marketed and used in legal metrology.
Accuracy VerificationChecking the measuring instrument
All measuring instruments used in legal metrology are subject to mandatory metrological control.
The fields of activity in which metrological control of measuring instruments is mandatory are determined by the Regulation on the category of measuring instruments subject to metrological control.
Hemeasurement controlIt is not mandatory for measuring instruments used for the purpose of controlling technological processes, scientific research and development, educational processes, exhibitions or for private use only.
To determine themeasurement accuracyof said measuring instrument, its owner may request a conformity assessment, which shall be carried out in order to verify the conformity of the manufacturer's declaration with the relevant standard or with the applicable metrological requirements.
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Initial verification and reverification of measuring instruments
All instruments used in legal metrology must be marked with a valid verification label or verification stamp.
Prior to commissioning, appropriate testing of each measuring instrument shall be performed.
If the instrument meets the requirements specified in the type approval, the verification seal will be stamped or glued on the instrument in the form of a label (label) indicating the reliability of the instrument.
initial verificationit will be carried out under the responsibility of the manufacturer or distributor of the measuring instrument or of an authorized foreign representative of the company when the instrument is marketed from consignment stocks.
The period of validity of the inspection will be limited to a certain period of time. The reversal periods are established in the Decree on the determination of the reversal intervals of measurement and standard instruments (Official Gazette No. 50/96).
Every two years, the weights ofclases E1, E2, F1, F2, F2, F2, F2, M1, M2, M3, as well as non-automatic weights corresponding to accuracy classes I, II and III and a maximum weight of up to 9000 kg will be presented for investment.
The water meters are designed to measure cold water with a flow rate of up to 10 m3/h every five years, gas every eight to six years, electricity every four to six years, etc.
The owner of the measuring instrument must pay attention to the fact that the investment of the instrument is always carried out on time.
The reversification instruments will be provided by the sectors ofmetrological controllocated in Rijeka, Zagreb, Split and Osijek, temporary verification centers for measuring instruments, accredited metrological laboratories, certified metrological laboratories or the place of installation of measuring instruments.
The metrological control sectors, in close collaboration with the market inspection, organize the periodic verification of the measuring instruments in the large municipal centers.
Inspecting a measurement device at a temporary verification center allows customers to save a significant amount of time and money.
The measuring device must be clean and ready for testing. Measuring instruments repaired by a service technician, whose metrology laboratory is certified, are controlled by authorized personnel at the facilities of the Metrological Control Sector.
The request for verification of these measuring instruments in the certified metrology laboratory must be submitted by the service technician.
Accredited metrological laboratories carry out verification work under the same conditions as the metrological control sector for those categories of measuring instruments for which permission has been granted from the State Service for Standardization and Metrology.
In the case of built-in measuring instruments, the verification request must be submitted by the owner.
The verification of said measuring instruments must be carried out on site by authorized personnel from the Metrological Control Sector. This also applies to highly sensitive measuring instruments, such as analytical weighing instruments.
The owner of the measuring instruments must provide auxiliary labor and measuring equipment for the tests.
The amount of fees and expenses during the verification process is established in the Regulation on the amount of fees and payment methods intended to cover the costs of testing measuring instruments, standards, samples of testing materials reference and measuring instruments (Official Gazette No. 49/92).
The inspection of measuring instruments in the premises of the metrological control sectors will be carried out daily. To save time, it is recommended to make an appointment in advance.
Conformity assessment of measuring instruments
Accredited and certified metrology laboratories assess the conformity of measuring instruments.
For some measuring instruments, the laboratories of the Department of Metrological Control carry out the conformity assessment.
The law does not provide for the conformity assessment of measuring instruments.
The owner of the measuring instrument requesting the conformity assessment must indicate in the request the documents for which he wishes the conformity of the measuring instrument to be verified (manufacturer's declaration, standard, metrological requirement, etc.).
If the instrument meets the requirements of the measurement object, it will be labeled with the following label.
To issue a declaration of conformity, an additional application must be submitted.
The owner shall require that the object be declared as proof of their approved quality assurance system.
basic metrology
In this part of the article, I am going to introduce you to the basics of quality maintenance.
This includes thequality assurance, quality control and metrology. We use quality assurance to ensure quality requirements are met.
Quality control is used to verify that the requirements are met. This is a subtle difference, and in practice these terms are sometimes used interchangeably. Metrology is the science of measurement.
This is how we can confidently compare measurement results from around the world.
These principles can be applied to products or services, but I am going to focus on production and how these three fundamental concepts relate to each other in this context.
So I've avoided the details of specific methods and I don't do math. I'll save this for the next article.
Origin of measurements
The Egyptians use regularly calibrated measurement standards to ensure that stones fit their large construction projects. But modern quality systems emerged during the industrial revolution.
Until then, mechanical products were made by craftsmen who processed each part individually to fit into the assembly.
This meant that each machine, and each part of it, was unique. If any part needs to be replaced, the master will have to install a new part.
At the end of the 18th century, French arms factories began to produce muskets with standard parts.
This meant that the army could carry spare parts and quickly replace them with broken ones.
These interchangeable parts were still installed for mounting, but instead of inserting each part into a separate gun, they were installed on the main part.
A few years later, American gunsmiths began using this method, but adapted it for their untrained workers. They prepared gauges for the reference part, workers set up production tools and machines using gauges, and used gauges to check the parts.
This allowed multiple machines, each performing a single operation with an unskilled operator, to produce precise parts. Parts could then be quickly assembled into complex machines.
Thus, the foundations of modern production were laid more than 100 years before Ford applied these ideas to a moving production line.
Calibration, actual value and measurement accuracy
The system of main parts, sensors and disposable machines worked when all the product was produced in the same factory.
Today's global value chains need a different system.
Instead of having a main physical part, we have a digital CAD drawing or model.
The specified tolerances provide the conformity of the details to each other and the workability at the time of appointment.
Instead of each manufacturer approaching a single reference part to customize their gauges, they calibrate them.
The tools are then used to assemble the production machines and check the produced parts.
The quality depends on this calibration process.
The most important concept to understand is that all measurements have uncertainty. If I asked you to calculate the height of this text, you would say:
âThis is about 4mm. The use of the word "or" implies some uncertainty in your evaluation.
In fact, we can never know the exact true meaning of anything, all measurements are actually estimates and have some uncertainty.
The difference between the measurement result and the actual value is themeasurement uncertainty. Since we can't know the true value, we can't know about the error either: they are unknown values.
All we can quantify about the world around us are the results of measurements, and they always have some uncertainty, even if this uncertainty is very small.
If you estimate the height of this text to be âabout 4mm, plus/minus 1mmâ, you have now defined some limits on your uncertainty. But you still can't be 100% sure it's true.
You can be some level of confidence, say 95%, that it is true. If you were to increase the limits, say, plus or minus 2mm, then your confidence would probably increase to 99%. Therefore, uncertainty gives us some limits, in which we can say with certainty that the true value lies in this.
Philosophy classes are over!
In one of the following articles, I'll talk more about these ideas and how to calculate uncertainty for a certain level of confidence.
uncertainty and quality
Once we have determined the uncertainty (or âaccuracyâ) of the measurement, we can use it to determine if the part meets the specified tolerance. Suppose the part is specified to be 100mm +/- 1mm. We measure it and obtain a result of 100.87 mm.
Is it part of the specification?
The simple answer is: âWe don't know if that's true, but perhaps there was an error in our measurements, and the part is in fact larger than 101mm. Maybe there was an even bigger mistake, and the pieces are actually less than 99mm!
If we don't know what measurement uncertainty is, we have no idea how sure we can be that the part is within specification.
Suppose the measurement uncertainty is obtained such that the measurement result is 100.87 mm +/- 0.1 mm with 95 percent confidence. We can now say with over 95 percent confidence that the part is within spec.
Therefore, understanding and quantifying measurement uncertainty is crucial to maintaining quality.
Now let's look at calibration and the associated concept of traceability. This is one of the fundamental aspects of uncertainty.
Calibration is a comparison with a reference sample and the uncertainty of this comparison must always be included for the reasons explained below.
A traceable measurement is a measurement that has a continuous chain of calibrations back to the primary standard.
In the case of length measurement, the basic standard is the determination of the measurer; the distance traveled by light in a vacuum in 1/299 792 458 seconds, as done by the International Bureau of Weights and Measures (BIPM) in Paris.
Since the 1930s, an inch has been defined as 25.4 mm, and thus can also be traced back to the same meter standard.
All measurements must be made according to the same standard to ensure that parts made in different countries fit together.
uncertainty and error
Uncertainty in measurement arises from different sources. Some of them will cause a permanent error or scrolling as a result.
For example, an unknown error that occurs when calibrating the instrument leads to a constant error when using the instrument.
This type of effect is known as systematic uncertainty, resulting in asystematic error. Other sources cause errors that change randomly with each measurement.
For example, air turbulence can lead to small randomly changing laser measurement disturbances, mechanical play and alignment can lead tomeasurement errorsrandomly changing mechanics.
This type of effect is known as random uncertainty leading to random error.
Typically, random uncertainty is divided into repeatability, random uncertainty of the results under the same conditions, and reproducibility, random uncertainty under changed conditions.
Of course, the conditions can never be exactly the same or completely different, so the differences between them are pretty vague.
The types of conditions that can be changed cause the measurement to be made at different times, with a different operator, with a different instrument, using a different calibration, and in a different environment.
There are two widely used methods to quantify measurement uncertainty.
Calibration laboratories and scientific institutions often perform uncertainty assessments according to the Uncertainty Expression in Measurements (GUM) guidelines.
The GUM method involves, first of all, taking into account all factors that can influence the measurement result.
Next, a mathematical model must be defined that determines the measurement result based on these influence values. Considering the uncertainty in each input variable and applying the "Law of Propagation of Uncertainty", it is possible to estimate the combined uncertainty of the measurement.
The GUM approach is sometimes described as a bottom-up approach, since it begins with a consideration of each individual impact.
Each impact is usually given in a table called the uncertainty budget, which is used to calculate the total uncertainty.
The processes ofindustrial measurementare normally evaluated using the Analysis method of theMeasuring system(MSA) recommended in the six signals methodology and, in general, in accordance with the recommendations of the MSA Manual of the Action Group of theAutomotive industry(AIAG).
The MSA includes Gage studies in which repeated measurements are compared to reference measurements under different conditions to determine uncertainty, repeatability, and sometimes reproducibility.
A Type 1 survey is a quick review, usually done for an initial understanding of the variation in meter readings. This is a single operator measurement of a single reference part calibrated 25 or more times, and then accounts for changes and uncertainty in the results.
This type of test is often called a non-MSA repeatability study.
The Gage Repeatability and Repeatability (R&R) study is used to gain a more detailed understanding of the measurement process.
Typically 10 parts are measured twice by at least three different operators. A statistical method called ANOVA is used to determine how much variation is caused by the instrument (âgaugeâ) and how much is caused by the operator.
The change of operator and the subsequent changes in time and environment are considered a complete representation of the reproducibility conditions.
MSA is sometimes referred to as a top-down method because it largely views the measurement process as a black box and experimentally determines systematic and random uncertainties.
Two important concepts in the MSA are precision used as the equivalent of uncertainty; and the precision used as the equivalent of the random uncertainty.
The advantage of estimating uncertainty is that it can account for all sources of uncertainty and, if done correctly, provides the most accurate estimate of uncertainty.
Problems with this approach include the fact that it requires a metrologist capable of building a mathematical model and the risk of human error that could lead to significant effects that could be misjudged or not accounted for.
The GUM method is also valid only for individual measurements that have been made with known values ââfor any correction. Therefore, it is difficult to correctly apply uncertainty estimation to predict the uncertainty of the industrial measurement process.
MSA is much easier to use and is designed to predict the accuracy of the industrial measurement process.
The problem with this approach is that some systematic effects are ignored and reproducibility conditions may not be fully represented, leading to underestimation of uncertainty.
An example of omitting systematic effects is that when determining the displacement, a comparison is made with a reference that is considered true; in fact, the reference also has an uncertainty that must be included.
This method is based on the fact that all reproducibility conditions change in such a way that their effect can be seen in the variation of the results of repeated measurements.
The way these conditions change may not fully reflect the changes observed throughout the actual measurement process.
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Measurement and quality assurance
So far I have focused on quality control, that is, how measurements can show that parts meet specifications after they have been manufactured.
Now let's briefly look at quality assurance, how we make sure that the process of producing good quality parts comes first.
This aspect of quality is largely addressed by theStatistical processes control(FCPC). The process can be evaluated by manufacturing various parts and measuring them to determine the variation and uncertainty of the production process.
Rather than giving these results directly, it is normal to divide the part tolerance by the process accuracy to allow machine tool (CP) or the process accuracy to allow machining (CPK).
The SPC is in many ways equivalent to an MSA. A top-down approach is required to understand random and systematic effects. However, instead of evaluating the results of the measurements, it is used to evaluate the results of the process.
Typically have the sameadvantages and disadvantagesthan an MSA, and an approach ofuncertainty assessmentfrom bottom to top if this raises concerns.
Initially, it may appear that there are fundamental differences between an MSA and an SPC due to the very different terms in an SPC.
However, a common cause variation (or a random cause of variation in the old literature) is equivalent to accuracy; a short-term variation is equivalent to repeatability; a long-term variation is equivalent to reproducibility; and a special cause of variation (or an attributed cause of variation in the older literature) is equivalent to bias.
The STC also pays much more attention to ensuring that the process is in "statistical control." Generally speaking, this means that the effects are random and are generally randomly distributed with any significant systematic effects being corrected for.
This is a strength of the STC and is sometimes overlooked in both the assessment of uncertainty and the assessment of management service agreements.
The main tool used in SPC to test the process "in control" is the control chart. This gives a simple graphical representation of the process, where you can easily see when the process drifts or makes errors that cannot be explained by normal random variations. For example, if all multipoints are increasing or decreasing, it means that the process is drifting.
In this article, I tried to give an overview of a large and complex topic.
I have introduced the fundamental principles underlying quality maintenance without going into the mathematics necessary to apply these methods.
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FAQs
What are the basic concepts of metrology? âș
Metrology is a wide reaching field, but can be summarized through three basic activities: the definition of internationally accepted units of measurement, the realisation of these units of measurement in practice, and the application of chains of traceability (linking measurements to reference standards).
What are the 3 main areas of metrology? âșMetrology can be divided into three subfields: scientific metrology, applied metrology, and legal metrology.
What is metrology the science of answer? âșMeteorology is the science dealing with the atmosphere and its phenomena, including both weather and climate.
What is metrology in your own words? âșMetrology comes from two Greek words: âmetronâ and âlogosâ which literally means âthe study of measurementsâ; it is the science of measurement.
What are the 5 basic elements of metrology? âșThe consensual metrological list of terms of the "International Vocabulary of Metrology (VIM)" is divided into five main headings: (1) quantities and units, (2) measurement, (3) devices for measurement, (4) properties of measuring devices, and (5) measurement standards (Etalons) [1].
What are the 5 basic metrology elements of a system? âș- Functional Elements of a Measurement System.
- Primary sensing element.
- Variable conversion element.
- Variable manipulation element.
- Signal conditioning element.
- Data transmission element.
- Data presentation element.
- Complete evaluation of newly developed products.
- Determination of the process capabilities and ensure that these are better than the relevant component tolerances.
- Determination of the measuring instrument capabilities andensure that they are quite sufficient for their respective measurements.
An example of this type of metrology might be seen in the production of products for the commercial industry, the testing and designing of aircraft, the functioning of large machinery, or even in factories using rotating equipment during the manufacturing of their products.
What is the most important thing about metrology? âșThe use of metrology minimizes errors and deviations by utilizing traceable, accurate reference standards to which calibration technicians can compare measuring instruments, thus enhancing the accuracy of the readings the instruments produce.
What is the purpose of metrology? âșWithout metrology, you can't discover, design, build, test, manufacture, maintain, prove, buy or operate anything safely and reliably. From filling your car with petrol to having an X-ray at a hospital, your life is surrounded by measurements.
What is metrology used for? âș
What is metrology? Metrology, in its broadest definition, is the science of measurement. In the context of modern manufacturing, metrology refers to quality assurance methods used to calibrate the machinery used during production and to measure the resulting parts.
Why is metrology used? âșIn simple terms, Metrology is the study or science of measurement. Metrology provides the quality assurance behind modern-day manufacturing processes. It is the science that enables production lines to produce thousands of identical pieces of sophisticated equipment.
How is metrology used in everyday life? âșMetrology gives us confidence in measurement results in such important areas as trade, health, safety, environmental monitoring, food safety, protection of consumer rights and law enforcement. People need to have confidence in the accuracy of the weights of products they buy.
What is a simple sentence for metrology? âșthe scientific study of measurement: He became involved in exact measurement and the establishment of standards in metrology. The company is the third largest U.S. supplier of metrology equipment.
Who uses metrology? âșMetrology is the study of measurements, and it is used in a variety of different industries including engineering, aerospace, manufacturing, energy, and healthcare.
What are the 5 uses of metrology to our daily lives? âșMetrology gives us confidence in measurement results in such important areas as trade, health, safety, environmental monitoring, food safety, protection of consumer rights and law enforcement.
What are the primary concerns of metrology? âșIt concerns the establishment of quantity systems, unit systems, the development of new measurement methods, development of measurement standards, and the chain of traceability from these reference standards to users in society. This can be considered as the highest level of metrology.