Introduction-to-Metrology

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• Meterology
• University

Imagine a mechanic is manufacturing a wheel bolt.

Which bolt can we send to the customer?

A

20.07 mm

B

19.99 mm

C

20.06 mm

D

21. 22 mm

We have to make sure that when we measure something, we can trust the measurement

Measurements & Metrology

Course code : MAE320

Credit units: 4

Course objective

Basic understanding of the metrology and tolerance design

Module 1: Principles of measurement

Module 2: Comparators

Module 3: Straightness and flatness

Module 4: Machine tool alignment and surface texture

Lesson Objectives

OVERVIEW

By the end of this session, you will be able to:

• Define metrology and distinguish between its three main branches.
  

• Evaluate the critical differences between accuracy and precision in engineering.
  

• Apply traceability principles to ensure international measurement standards.

Three Branches of Metrology

Scientific

Establishes fundamental units, scientific methods and primary standards of measurement.

Industrial

Applies measurement science to manufacturing processes, quality control and production.

Legal

Enforces statutory requirements for units, measuring instruments and commercial transactions.

Accuracy Versus Precision

High Precision, Low Accuracy

Measurements are repeatable and close to each other, but consistently far from the true reference value. Indicates systematic bias.

High Precision, High Accuracy

Measurements are both highly repeatable and centered precisely on the true value. Represents ideal measurement performance.

Drag and Drop

High accuracy Low precision

Low accuracy Low precision

Uncertainty and Error

ANALYSIS

All measurements contain uncertainty. No reading is absolute.

• Systematic errors: shift results consistently due to faulty calibration.

• Random errors: cause unpredictable variations from noise.

⚠️

Watch out

High precision fails if tools introduce systematic error.

Traceability Chain

Traceability links a workshop measurement to international standards through an unbroken chain of comparisons.

SI Units

International System definitions base units on natural constants.

National Standard

Primary laboratories maintain master reference equipment.

Calibration Lab

Accredited facilities calibrate secondary working standards.

Factory Floor

Shop-floor instruments measure daily production parts.

Drag and Drop correct SI units

Second

Meter

Kelvin

Kilogram

Length

Mass

Temperature

Time

Summary

Key Concepts Retained

• Metrology underpins quality, trade and manufacturing.

• Accuracy is closeness to truth; precision is consistency.

• Traceability chains ensure universal unit consistency.

🧠

Remember

Next, we will examine Coordinate Measuring Machines (CMM) and laser scanning technologies.