Introduction to Metrology

Metrology Definition

• "Metrology" originates from the Greek words "metron" (measure) and "logos" (study or discourse).
• Metrology involves studying measurement units, accuracy, precision, and ensuring measurements are consistent and reliable.
• Metrology is important for ensuring standardized and comparable measurements across science, engineering, medicine, and manufacturing.

Metrology in Precision Machining

• Metrology is critical in precision machining to ensure components meet exact specifications with high accuracy.
• It provides the tools and methods to measure and verify parts at every production stage.

Maintenance of Metrology Tools

• Maintaining metrology tools is crucial for accuracy, reliability, and longevity to avoid errors.
• Proper maintenance prevents defects, quality control issues, and costly rework.

Cleaning

• Instruments must undergo regular cleaning to prevent dirt, oil, dust, or shavings, which can affect measurement accuracy.
• Use a lint-free cloth and non-abrasive cleaners for metal surfaces on micrometers, calipers, and other measuring tools to remove contaminants.
• CMMs and optical devices require careful cleaning, including wiping probes or lenses.

Calibration

• Metrology tools should be calibrated against known standards regularly (usually annually or more frequently, depending on the tool).
• Calibration ensures consistent readings that align with recognized measurement standards.

Environmental Conditions for Instruments

• Instruments must be stored and used in controlled environments with minimal fluctuations in temperature, humidity, and vibration.

Temperature

• Many metrology instruments like CMMs and optical devices are sensitive to temperature changes.
• Metals expand and contract with temperature variations, affecting measurements.
• Metrology labs often use climate-controlled rooms or temperature-controlled surfaces to minimize these effects.

Vibration and Dust

• Instruments should be stored in clean, vibration-free environments because precision equipment like CMMs can be affected by vibrations, leading to measurement errors.

Regular Inspection for Wear and Tear

• Tools with moving parts, such as micrometers, calipers, and height gauges, are checked for wear and replaced or serviced if necessary.
• Measuring surfaces are kept free from scratches, dents, or burrs, which can affect measurement accuracy.
• Probes on CMMs are sensitive and inspected for damage or wear, replaced or recalibrated if necessary.

Lubrication and Protection

• Some tools, like micrometers and calipers, may require occasional lubrication to maintain smooth operation and prevent corrosion.
• Excess lubricant should be avoided because it could interfere with measurements or attract dirt.
• Instruments should be protected from rust, especially when exposed to moisture, using a protective oil or rust-preventative coating.

Periodic Software Updates for Digital Instruments

• Modern digital metrology instruments rely on software for measurements and data analysis, requiring periodic software updates, to performs correctly and avoid errors.
• Built-in diagnostic tools or self-check routines should be run regularly to verify that all components are functioning correctly on advanced instruments, such as CMMs and digital micrometers.

Handling

• Handle instruments carefully, especially those with fine measuring faces or delicate components like optical comparators and CMM probes).
• Dropping or knocking tools can lead to calibration errors or permanent damage.

Storage

• Instruments should be stored in designated cases or in clean, dust-free environments to prevent accidental damage.

Avoiding Shock and Impact

• Metrology tools should not be exposed to shocks, as even minor impacts can affect the precision of the instrument.

Direct Measurement Instruments

• Direct measurement instruments provide a direct value immediately.
• Examples include calipers, micrometers, height gauges, optical comparators, and torque wrenches.

Indirect Measurement Instruments

• Indirect measurement instruments measure related properties or quantities, while the final value is derived through calculations.
• Examples include CMMs, laser scanners, strain gauges, flow meters, and temperature sensors.

SI Units

• The SI units (International System of Units) are the standard set of units used worldwide.
• The SI system is based on seven fundamental units, from which all other units can be derived, ensuring uniformity and clarity.

Meter (m) - Unit of Length

• Definition: The meter is the SI unit for length or distance, precisely defined as the distance that light travels in a vacuum in 1/299,792,458 of a second.
• Use: The meter is used to measure distance, height, depth, and width in everyday life and scientific applications.
• Example: Measuring table length, distance between cities, or building height.

Kilogram (kg) - Unit of Mass

• Definition: The kilogram is the SI unit for mass, defined by the mass of a platinum-iridium cylinder stored in France.
• Use: The kilogram is used to measure mass in various applications, including weight measurement and scientific experiments.
• Example: Measuring the mass of a person, a bag of rice, or a planet.

Second (s) - Unit of Time

• Definition: The second is the SI unit for time, defined as the duration of 9,192,631,770 periods of radiation corresponding to the transition between two hyperfine levels of the ground state of the cesium-133 atom.
• Use: The second is used to measure the passage of time in everyday life, scientific experiments, and technological systems.
• Example: Measuring the duration of a minute (60 seconds), time for a chemical reaction, or time between events.

Ampere (A) - Unit of Electric Current

• Definition: The ampere is the SI unit for electric current, defined as the constant current that produces a force of 2 x 10^-7 newtons per meter of length between two straight parallel conductors of infinite length.
• Use: The ampere measures the flow of electric charge in a circuit. Essential for understanding electrical phenomena.
• Example: Measuring the current flowing through a wire in an electrical circuit.

Kelvin (K) - Unit of Temperature

• Definition: The kelvin is the SI unit for temperature, defined as 1/273.16 of the thermodynamic temperature of the triple point of water; the Kelvin scale starts at absolute zero.
• Use: Kelvin is used primarily in scientific and engineering contexts, where precise and absolute temperature readings are needed.
• Example: Measuring the temperature of gas, heat from scientific experiments, or space temperatures.

Mole (mol) - Unit of Amount of Substance

• Definition: The mole is the SI unit for the amount of substance. The mole is specifically the amount of substance that contains as many entities (atoms, molecules, or ions) as there are in 12 grams of carbon-12.
• Use: The mole is used to measure the quantity of chemical substances, particularly in chemistry, biology, and physics.
• Example: Measuring the number of molecules in a substance or moles of a chemical element in a reaction.

Candela (cd) - Unit of Luminous Intensity

• Definition: The candela is the SI unit for luminous intensity. The candela is defined as the luminous intensity of a source emitting monochromatic radiation of frequency 540 × 10^12 Hz and has a radiant intensity of 1/683 watt per steradian.

Derived SI Units

• The SI system includes derived units formed by combining base units.

Newton (N) - Unit of Force

• 1 N = 1 kg·m/s² (kilogram meter per second squared).
• Used to measure force.

Joule (J) - Unit of Energy

• 1 J = 1 N·m (Newton meter).
• Used to measure energy, work, or heat.

Watt (W) - Unit of Power

• 1 W = 1 J/s (Joule per second).
• Used to measure the rate of energy transfer (power).

Pascal (Pa) - Unit of Pressure

• 1 Pa = 1 N/m² (Newton per square meter).
• Used to measure pressure, stress, or tension.

Hertz (Hz) - Unit of Frequency

• 1 Hz = 1 cycle per second.
• Used to measure frequency (such as the frequency of sound or electromagnetic waves).

Coulomb (C) - Unit of Electric Charge

• 1 C = 1 A·s (ampere second).
• Used to measure electric charge.

Volt (V) - Unit of Electric Potential

• 1 V = 1 J/C (joule per coulomb).
• Used to measure electric potential or voltage.

Ohm (Ω) - Unit of Electrical Resistance

• 1 Ω = 1 V/A (volt per ampere).
• Used to measure the resistance in electrical circuits.

SI Prefixes

• The SI system uses prefixes to represent large or small quantities; these modify the base unit by powers of 10.
• Common prefixes include kilo (k), mega (M), giga (G), milli (m), micro (μ), nano (n), and pico (p).

Definition of the Meter

• The meter (m) is the fundamental unit of length in the International System of Units (SI).
• It is defined as the distance that light travels in a vacuum in 1/299,792,458 of a second, based on the constant speed of light.

Multiples and Submultiples of the Meter

• The SI system uses prefixes to measure scales of length efficiently.

Anglo-American (Imperial) System

• The Anglo-American system, known as the Imperial System or U.S. Customary Units, is used in the United States, Liberia, and Myanmar.
• Usage includes the Imperial System historically used in Britain and the U.S. Customary System used in construction, road signs, and measurements in the United States.

Unit Conversion

• Conversion between the metric system and the Imperial system is essential in engineering, science, and international trade.
• Formulas include inches to centimeters: cm = in x 2.54

Conversion of Physical Quantities

• Physical quantities are converted between different unit systems, such as the International System of Units (SI) and the Imperial (Anglo-American) system.

Temperature Conversion

• Temperature is measured in Celsius (°C), Fahrenheit (°F), and Kelvin (K).
• Conversion formulas include Celsius to Fahrenheit, Fahrenheit to Celsius, Celsius to Kelvin, and Kelvin to Celsius.

Density Conversion

• Density is mass per unit volume, expressed in kg/m³ (SI unit) or g/cm³, lb/ft³ (Imperial unit).

Electrical Unit Conversion

• Electrical quantities include current (A), voltage (V), resistance (Ω), power (W), and charge (C).

Torque Conversion

• Torque measures rotational force, expressed in Newton-meters (N·m) in SI and pound-force feet (lb-ft) in the Imperial system.

Revolutions per Minute (RPM) Conversion

• RPM measures the number of complete rotations per minute.

Angular Velocity Conversion

• Angular velocity is measured in radians per second (rad/s) or degrees per second (°/s).

Pressure Conversion

• Pressure is the force per unit area, expressed in Pascal (Pa) in SI or psi (pounds per square inch) in the Imperial system.

Time Conversion

• Time is commonly measured in seconds, minutes, hours, days, and years.

Measurement Error (Definition)

• Measurement errors occur when the value obtained in a measurement differs from the true or expected value.
• Errors arise from instrument-related issues, environmental factors, and human errors.

Errors Due to the Measuring Instruments

• Result from misalignment, design flaws, wear, and contact precision
• Can lead to inaccurate readings

Alignment Error (Error of Misalignment)

• Misalignment errors occur when the measuring instrument is not correctly positioned relative to the object being measured.
• This can happen due to incorrect positioning of the instrument, parallax error, and deviation of the instrument's axis from the measurement axis.

Design and Manufacturing Error

• These errors are due to imperfections in the construction of the measuring instrument, which may result from defective components, manufacturing tolerances causing slight variations from one instrument to another and improper calibration during the production process.

Wear Error of the Instrument

• Measuring instruments experience mechanical wear, which can affect their precision, includes repeated use, friction between moving parts and deformation of materials, especially in instruments made of soft metals.

Precision and Contact Shape Error

• The precision of the measurement depends on the accuracy of the instrument's contact surfaces with the object being measured.
• Errors in contact can result from an incorrect shape of the measuring tips, surface roughness, and inconsistent pressure.

Measurement Errors Due to the Operator

• Occur when human factors lead to incorrect readings or inconsistencies in measurement results, which can come from misreading, improper handling, inconsistent applications, or environmental influences

Reading Error

• Operator misinterprets the measurement scale or displayed value due to parallax error when the observer's eyes not aligned perpendicularly to the measuring scale, incorrect interpretation of digital or analog displays, and rounding errors when estimating between scale divisions

Handling Error

• Improper handling of the measuring instruments leads to variations in the result, this may be caused by applying excessive or insufficient pressure, holding the instrument incorrectly or not ensuring that the measuring surfaces are clean

Fatigue and Lack of Concentration

• Human fatigue and a lack of focus can significantly impact measurement accuracy
• May result to slower reaction times, skipping steps in the measurement process, and failure to notice small deviations or errors

Measurement Errors Due to Environmental Factors

• Environmental conditions significantly impact the accuracy of measurements, as factors such as temperature variations, external agents, humidity, atmospheric pressure, and contamination can alter the performance of measuring instruments and the objects being measured
• Temperature: Temperature changes can cause the expansion or contraction of materials which affects the measuring instrument and the object being measured

Measurement Errors due to Geometric tolerances of the part

• Errors in measurement can also arise due to geometric variations in the part being measured and these errors results from deformation, shape irregularities, material aging, and internal structural changes due to thermal treatments

Deformation Errors

• Occur when a part changes shape due to external forces, residual stresses, or improper handling during measurement which can be caused by elastic deformation, residual stresses or incorrect clamping and holding the part during measurement

Shape Errors

• Occur when a part does not meet the intended geometric specifications which affect measurement accuracy and these errors includes flatness and Cylindricity

Stabilization or Aging Errors

• Some materials undergo dimensional changes over time due to internal stress release or environmental exposure
• Causes include residual stresses from machining, material relaxation over time and exposure to environmental factors

Internal Structural Changes Due to Heat Treatment

• Thermal treatments can alter a material's internal structure which affects its dimensions and mechanical properties
• Causes includes expansion and contraction, changes in grain structure or phase transformation in metals

Direct Measuring Instruments

• Vernier are precision instruments use in measuring external, internal, and depth dimensions with high accuracy.
• Goniometer is used to measure angles with high precision
• External micrometers are instruments use in measuring external dimensions of small components and feature a spindle and anvil
• Internal Micrometers instruments are used to measure internal diameters of bores and holes, extending rods or three-point contact system, and precision screw mechanism for fine adjustments

Graduated Ruler (Steel Rule)

• It is a simple and straight-edged tool in measuring small components and and marking line straightness

Gauge Blocks (Slip Gauges, Jo Blocks)

• Are high precision tools used for calibration in micrometers, calipers, and dial

Thickness Gauges (Feeler Gauges)

• Instruments use in measuring the clearance between two surfaces

Combination Square

• It is a multi-purpose tool in measuring for straightness, angles, and depth measurements

Indirect Measuring Instruments

• Used in precision machining, quality control, and metrology and do not provide numerical readings instead compares and analyzes measurement based on reference standard
• Optical comparators are non-contact instruments which light source and lens to allow for comparison against standard profiles or digital overlays

Roughness Tester (Surface Roughness Gauge-Rugosimeter)

• Instruments use in measuring texture and finish of surface by scanning with a stylus and laser sensor
• Bevel Square are instruments use in transferring and checking angles rather than measuring them directly
• Sine Bar are precision tools that are use in measuring and setting angles