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# Basics of Dimensional Metrology

The presentation deals with the basics of Dimensional Metrology.
The presentation includes the basic terminologies , including the following:
Measurement uncertainty: Understanding how to evaluate and report measurement uncertainty, which is the level of confidence in a measurement result.

Statistical analysis: Knowledge of basic statistical concepts, such as mean, standard deviation, and normal distribution, and their use in dimensional metrology.

Tolerance analysis: Understanding of tolerance limits, and how to apply them in dimensional measurements to determine if a part is acceptable or not.

Measurement systems analysis: Knowledge of how to evaluate the performance of measurement systems and identify sources of error.

The presentation deals with the basics of Dimensional Metrology.
The presentation includes the basic terminologies , including the following:
Measurement uncertainty: Understanding how to evaluate and report measurement uncertainty, which is the level of confidence in a measurement result.

Statistical analysis: Knowledge of basic statistical concepts, such as mean, standard deviation, and normal distribution, and their use in dimensional metrology.

Tolerance analysis: Understanding of tolerance limits, and how to apply them in dimensional measurements to determine if a part is acceptable or not.

Measurement systems analysis: Knowledge of how to evaluate the performance of measurement systems and identify sources of error.

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### Basics of Dimensional Metrology

1. 1. Dimensional Metrology
2. 2. Table of Contents • Introduction • Basic Terminologies • Inspection Process • Measurement Process Validation
3. 3. Introduction • In 1999 NASA sent a mission to MARS • Climate Orbiter • It completed its 99% of journey • Fired steering rocket to control its final approach • However, the thrust value had a Martian Blunder
4. 4. Introduction • 1776 war of independence • Had to deliver 10000 muskets in two years • With no factory • Did it in 10 years • Then took the order of 15000 muskets and delivered them in two years Eli Whitney Order of Muskets
5. 5. Introduction The need
6. 6. “When you measure what you are speaking about and express it in numbers, you know something about it, but when you cannot express it in numbers your knowledge is of a meagre and unsatisfactory kind...” Lord Kelvin (1824~1907) Introduction The need
7. 7. As a result of its importance, measurement has a science of its own, called metrology, from the Greek words metron (‘measure’) and logos (‘study’) Introduction Metrology
8. 8. Introduction Measurement Domain
9. 9. BASIC TERMINOLOGIES Error & Uncertainty Error is the diﬀerence between the measured value and the true value of the thing being measured Uncertainty is the parameter, associated with the result of a measurement, that characterizes the dispersion of the values that could reasonably be attributed to the measurand. Whereas,
10. 10. BASIC TERMINOLOGIES Accuracy & Precision
11. 11. BASIC TERMINOLOGIES Resolution The resolution of an instrument is a quantitative expression of the ability of an indicating device to distinguish meaningfully between closely adjacent values of the quantity indicated.
12. 12. BASIC TERMINOLOGIES Trueness Trueness is a similar concept to accuracy, but while accuracy refers to the closeness between an individual measurement and the true value, trueness refers to the closeness of agreement between the average value obtained from a set of test results and the true value.
13. 13. BASIC TERMINOLOGIES Repeatability Repeatability is the closeness of agreement between repeated measurements of the same thing, carried out in the same place, by the same person, on the same equipment, in the same way, at similar times.
14. 14. BASIC TERMINOLOGIES Reproducibility Reproducibility is the closeness of agreement between measurements of the same thing carried out in diﬀerent circumstances, e.g. by a diﬀerent person, or a diﬀerent method, or at a diﬀerent time
15. 15. BASIC TERMINOLOGIES Confidence Level Make a number of measurements of something – like the concentration of carbon monoxide gas in your vicinity – True value lies between, say, 9 parts per million (ppm) and 11 ppm – probably (or 10±1 ppm). You could not be sure that this was the case, but you could express your confidence that it is. So you might decide that you are 90% confident that the answer lies between those values.
16. 16. BASIC TERMINOLOGIES Tolerance A tolerance is the maximum acceptable difference between the actual value of some quantity, and the value specified for it.
17. 17. BASIC TERMINOLOGIES Validation Validation is confirmation that some aspect of a measurement process is fit for purpose. Verification Verification is making measurements to ensure conformance to specifications.
18. 18. BASIC TERMINOLOGIES Calibration Comparison of an instrument against a more accurate one (or against a reference signal or condition), to find and correct any errors in its measurement results.
19. 19. BASIC TERMINOLOGIES Accreditation Accreditation is the independent, third-party evaluation of a conformity assessment body (such as certification body, inspection body or laboratory) against recognised standards, conveying formal demonstration of its impartiality and competence to carry out specific conformity assessment tasks (such as certification, inspection and testing).
20. 20. BASIC TERMINOLOGIES Certification Certification is the provision by an independent body of written assurance (a certificate) that the product, service or system in question meets specific requirements.
21. 21. INSPECTION USES • Document Changes in process performance • To distinguish between good lots and bad lots • Distinguish between good product and bad product • Determine status of process control • Evaluation of process capability / adjustment of process • To rate accuracy of inspectors / inspection equipment
22. 22. INSPECTION PROCESS What to measure? Instrument Selection Knowledge of MSA Rounding Rules Inspection Stage Errors in inspection Sampling Regular Review Traceability of Inspections
23. 23. INSPECTION PROCESS What to measure? • Measurement is made for a reason • It needs to be defined and understood • Only then can a right measurement be made
24. 24. INSPECTION PROCESS What to measure?
25. 25. INSPECTION PROCESS Instrument selection
26. 26. INSPECTION PROCESS Knowledge of MSA • Measurement System Validation • Repeatability & Reproducibility (ISO5725-1,2: 2019) • Uncertainty of the measurement (ISO 21748: 2017) • Proficiency Testing • Comparison with other results
27. 27. INSPECTION PROCESS Knowledge of MSA (ISO14253)
28. 28. INSPECTION PROCESS Knowledge of MSA (ISO14253)
29. 29. INSPECTION PROCESS Rounding Rules (ASTM E29)
30. 30. INSPECTION PROCESS Rounding Rules (ASTM E29)
31. 31. INSPECTION PROCESS Sampling Sr. # Characteristic MIL-STD- 105 E MIL-STD-1916 ISO 2859 ISO 3951 1. Basics Attributes Attribute / Variables Attributes Variables 2. Acceptance Criteria # of Non Conformin g products / AQL # of Non Conforming Products or s- characteristic / verification levels No. of Non Conforming Products / AQL S- characteristi c / AQL 3. Distribution Any Any Any Normal only 4. Sample Sizes Standard Tables Follows 105 E Follows 105 E Different (usually smaller) 5. Switching Standard Follows 105 E Slightly Different Different
32. 32. INSPECTION PROCESS Inspection stages • Incoming • Final • Pre Process • Post Process • Verification Inspection
33. 33. INSPECTION PROCESS Measurement Errors Temperature Compensation
34. 34. INSPECTION PROCESS Measurement Errors Cosine Error
35. 35. INSPECTION PROCESS Measurement Errors Sine Error
36. 36. INSPECTION PROCESS Measurement Errors Abbe Error
37. 37. INSPECTION PROCESS Measurement Errors Elastic Compression
38. 38. INSPECTION PROCESS Measurement Errors Parallax Error
39. 39. INSPECTION PROCESS Regular Review • Check Instruments • Check Measurement Procedures • Inspection Audit
40. 40. INSPECTION PROCESS Inspection Traceability • Keeping Controlled Records
41. 41. Six Guiding Principles Regular Review • Check Instruments • Check Measurement Procedures Demonstratable Consistency • Gauge R&R Studies • Proficiency Testing • Regularly Analyse factors that could effect measurements
42. 42. Six Guiding Principles The Right Procedures • Written Procedures of measurement • Include risk assessment in the procedure
43. 43. Building Blocks of Measurement System Analysis 1. Measurement System Validation a) Accuracy (ISO 5725-1: 2019) b) Repeatability & Reproducibility (ISO 5725-2: 2019) 2. Uncertainty Assessment (ISO 21748:2017) 3. Comparison of results with other methods 4. Proficiency Testing