FUNDAMENTAL OF METROLOGY

Devices, measures qty & units in our daily life i.e. home, office and workplace, to name a few:

INTRODUCTION

NEEDS FOR METROLOGY IN MANUFACTURING INDUSTRY

Industrial Inspection: Concerns with various insp. & tech. due to rapid industrial revolution.

QC: Precise parts, tight tolerances & prod. specs to satisfy customers as essential component in QC.

CQI: Dynamic metrology lead to development of precision inspection instruments.

Market Globalization: In doing biz internationally, we depend on measures and quantity being standardized throughout various countries.

INTERNATIONAL SYSTEM OF UNITS (SI)SI or Metric System is a system built upon a foundation of seven base units:

Physical QuantityUnitSymbolLengthMetermTimeSecondsTemperatureKelvinKMassKilogramkgCurrentAmpereALuminous IntensityCandelaCdAmount of SubstanceMolemol

Direct Measurement- value obtained directly from instruments scale.- no need mathematical calculation.- i.e. measuring dim. using line-grad instruments.Indirect Measurement- measuring parameters directly.- determine value from mathematical calculation.- i.e. angle measurement using sine bar method.Comparative Measurement- compare the standard (i.e. gauge blocks) and the work piece.

CLASSIFICATION OF MEAS. METHODS

MEASUREMENT ERRORSSources of Errors:

Human Errors: result from the physical nature of workmanship of the operator.- Reading Errors (i.e. parallax).- Alignment Errors (i.e. zero offset).

Instrumental Errors: result from the limitations in the hardware compared to ideal instruments.- Loading Errors and Wear Errors.

Environmental Errors: result from the effect of surrounding temperature, pressure and humidity.- Other external influences i.e. vibration, magnetic field etc.

BASIC TERMINOLOGY OF MEAS.

TerminologyDescriptionAccuracyThe degree of closeness of the measured size with its true value as expressed in standard units of measurementNominal SizeLimit size of a part or workpiece in accordance to its functionTrue SizeTheoretical size in which free from measurement errorsActual SizeValue of size obtained through measurementApproximate SizeValue of size obtained with errors exceeding permissible errorsMeasurement uncertaintyMeasurement results which state the range of values within true valueMeasurement errorDifference between true values with value through measurementsMeasurement ReliabiltyQuantitative characteristics which implies confidence in the measured results

Accuracy : How close the measurement reading is to the actual true value of that measurement.Precision:The degree to which the instrument will repeat the same measurement over timeACCURACY VS. PRECISION

The equipments should be consistently cleaned to eliminate the measurement errors.

Proper handling of equipment by referring to user manual is essential to avoid the equipment form easily damaged.

When the equipment is not in use, it should be protected from atmospheric corrosion.

Do not use the equipment as a hand tool.

Calibrate the equipment periodically before use.

GENERAL CARES & HANDLING

1) Steel Ruler & Measuring TapeThe most basic measuring devices in the workshop.Steel ruler a.k.a machinist s rule.Steel ruler is a metal strip with notches along the edge that indicate increments of measurement.Scale Reading: Most steel rulers and measuring tapes have English measurements along one side and metric measurements along the other.BASIC DIMENSIONAL METROLOGY

Caliper = a long section and pair of jaws with measurement markings.Types: i.e. vernier caliper etc.Measuring Scale (Fig 3): measuring range: 0 300mm, measuring accuracy: 0.1 0.02mm1)3 types of std. vernier: 1/10mm, 1/20mm, 1/50mmmain scale: distance of 50mm is divided into 50 equal parts, thus distance btw. marking = 50mm/50equal parts = 1mm.2)vernier scale: distance btw. marking = 49mm/50equal parts = 0.98mm, thus measuring accuracy = 1mm 0.98mm = 0.02mm.

2) CALIPER

PART OF VERNIER CALIPER

ELECTRONIC VERNIER CALIPER

HOW TO READ

Main Scale:A = 0.00 mmVernier Scale:B = (15 x 0.02 mm) = 0.30 mmOverall Reading : C = 0.00 mm + 0.30 mm = 0.30 mmEXAMPLE 1: VERNIER CALIPER READINGS

EXAMPLE 2: VERNIER CALIPER READINGS

TRY YOUR SELF

TRY YOUR SELF

Use screw threads to achieve higher amplification.

Types: i.e. external micrometer etc.

Measuring Scale: measuring range: 0 25mm, 25 50mm, 50 75mm, 75 100mm and up to 475 500mm, measuring accuracy: 0.001 0.010mm

1)length of the spindle threads = 25mm, thus measuring ranges are stepped at every 25mm.

2)thimble = 50 graduations; spindle = 0.5mm pitch. If thimble is rotated 1 complete revolution, spindle will move 0.5mm.

3)1 graduation on thimble scale represents 0.01mm in terms of measuring accuracy, or measuring accuracy = 0.5 spindle pitch/50 graduations = 0.01mm

3) MICROMETER

EXAMPLE 1 & 2: MICROMETER READINGS (W/O VERNIER SCALE)

(1)Upper Scale on the sleeve= (15 x 1 mm graduation =15 mmLower Scale on the sleeve= (1 x 0.5 mm graduation) =0.5 mmReading on the thimble= (22 x 0.01 mm graduations) =0.22 mmOverall Reading= (15 + 0.5 + 0.22) mm =15.72 mm(2)Upper Scale on the sleeve= (17 x 1 mm graduation =17 mmLower Scale on the sleeve= (0 x 0.5 mm graduation) =0.0 mmReading on the thimble= (41 x 0.01 mm graduations) =0.41 mmOverall Reading= (17 + 0.0 + 0.41) mm =17.41 mm

EXAMPLE 3: MICROMETER READINGS (WITH VERNIER SCALE)

Sleeve:6 mmThimble:0.21 mmVernier:0.003 mmOverall Reading:(6 + 0.21 + 0.003) mm = 6.213 mm

A bevel protractor is a graduated circular protractor with one pivoted arm; used for measuring or marking off angles. The bevel protractor is used to establish and test angles to very close tolerances. It reads to 5 minutes or 1/12and can measure any angle from 0 to 360.

BEVEL PROTRACTOR

The bevel protractor enables angles to be measured to an accuracy of 5 minutes (60 minutes = 1 degree).The angle between the _movable arm and the stock is measured on the protractor scale, a vernier giving greater accuracy. The protractor scale is graduated in degrees from each end, meeting at 90 degrees in the middle. This enables "right handed" or "left handed" angles to be measured.

HOW TO READ BEVEL PROTRACTOR

Before an angle is measured, the accuracy of the bevel protractor should be verified by inserting the blade and straight edge to a right angle with the aid of a Master Square and then checking the position of the vernier index mark relative to the protractor scale. Any slight error may be corrected by adjusting the vernier scale position.To read the protractor, read from the 0 on the protractor scale to the 0 on the vernier scale. This gives the number of degrees. Then read the vernier scale in the same direction till the coinciding line is met. The number of the coinciding line (indicating minutes) must be added to the degrees read from the protractor scale. HOW TO READ BEVEL PROTRACTOR

HOW TO READ BEVEL PROTRACTOR

Discussed the meaning of a) Accuracyb) Repeatability c) Direct measurementd) Indirect measurement

Discussed the important of Metrology in the scope ofIndustrial InspectionCustomer RequirementQuality ControlContinuous ImprovementMarket Globalization

EXERCISE