MQC (Metrology and Quality Control )• InSem -30 marks

• Oral – 25 marks

• EndSem- 70 marks

What is Metrology?

A Greek word

Science of precision measurement

For engineer, it is science of measurement of lengths and

angles and all related quantities like width, depth, diameter,

straightness, roundness, etc., with high accuracy.

Who Needs Accurate Measurements?

Pharmaceutical Industry

• Metrology laboratories test weights and volume standards for pharmaceutical companies

• Products include medicines like aspirin, antibiotics, vaccines, insulin, & vitamins

Defense Industry

• Metrology laboratories test standards for many military and defense companies

• These companies make the guidance systems for the Patriot missiles and other things that are

top secret

Space Station, Satellites….

• Metrology laboratories test standards for many companies that provide parts of the space shuttle

• These parts include the metal, heat shield, electronics, fabrics, o-rings, optics, and tires

Retail Measurements

• State metrology laboratories test standards used to test retail scales and meters

• These include gas pumps, produce scales, milk, bread and other packaged items, and price scanning systems

Almost Everybody!

Production Circuit

Research and development

Metrology within research and development

is important to

Avoid defective goods later on

Validate process

Check scientific theories

Construction, adjustment, acceptance test

Within this step metrology checking:

If production machines are located

according to plant layout

If machines components are located

properly

If production moulds and tooling

profile are within tolerance

Single part inspection

A single part- a lot of geometries to be check, it involves:

Shape of the parts

Angularities

Drilling position

Milling outline

Assembly of parts

Metrology helps in assembling parts accurately:

Upto this point everything fits perfectly and

functions smoothly- in theory

However, when assembling parts, inexplicable

gap occurs. Metrology help in avoiding, fingering

out, eliminating these cause

Now, a couple of definitions…

“the science that deals with measurement”

“to determine the dimension, quantity or capacity of

something”

Measure

Metrology

SEVEN BASE UNITS (SI)

Mass Kilogram (kg)

Length Meter (m)

Time Second (s)

Temperature Kelvin (K)

Electric Current Ampere (A)

Amount of Substance Mole (mol)

Luminous Intensity Candela (cd)

Accuracy and Precision

• Accuracy is how close an individual value is to the true or accepted value

• Precision is the consistency of a series of measurements

Gage R&R

• Terms in gage R&R

Gage – a gage is any device that is used to obtain measurement.

Repeatability – is ability of measuring instrument to give the samevalue of reading repetitively over a period of time with the samemeasurement conditions, same instrument and observer, samelocation and same condition of use maintained throughout.

Reproducibility –relates to the closeness of output reading for thesame input when there are changes in the method of measurement,observer, measuring instrument, location, condition of use and time ofmeasurement.

Uncertainty

• Denotes the degree of accuracy with which the measurement has made

• Error = true value – measured value

• Instead of specifying measurement error, it is common practice to denote the range of error.

• This region in which error is estimated to lie is called uncertainty

• Example, 100 ± 1.2

Principle of Measurement

Traceability • Traceability means that a measured result can be related to stated

reference, usually national or international standard through anunbroken chain of comparison, all having stated uncertainties.

• Traceability gives the user confidence that his/her measurementsagree with the national standards within the stated uncertainty.

• It also ensure that the measurements will be equivalent to thosemade using different instruments from different suppliers.

• This is particularly important when importing or exporting goods.

Standards of Measurement

Types of standards

1. Primary standards(reference standard)

2. Secondary standards(calibration standard)

3. Tertiary standards(inspection standard)

4. Working standards(working standard)

Line standard

• Distance measured between two parallel lines or surfaces

• Example – meter tape, vernier

• Distance is measured between the line which matches with zero and the line which matches with the point which is to be measure

Line standard

Meter Yard

Meter

• It is distance between center position of two lines etched on a polished surface of a bar of pure platinum alloy(90%) and iridium alloy (10%).

• 1 meter = 1.09361 yard

Yard

• Yard is bronze bar with squarecross-section.

• The yard is distance between twocentral transverse lines on theplugs when the temperature ofbar is at 62 degree F.

• 1 yard = 0.9144 meter

End standards

• Distance is measured as separation of two parallel surfaces

• Examples – limit gauges, slip gauges

• Accurate and specially used in industries

• Small distance measuring capacity

Wavelength standard

• Sometimes error may occurs due to-

variation in size of gauge

Variation in temperature, pressure, overall environment

• Use of wavelength monochromatic light which isnatural and static unit of length as a workingstandard will reduce errors.

• 1 meter = 1650763.73 X wavelength of radiation

Error

• Error is the difference between a measured value and the “true” value

% error = True value – measured value X 100%

True value

Sources of Error1. Defects in instruments

2. Manual adjustment of instruments

3. Manufacturing error in instruments

4. Environmental effects

5. Human errors

6. Error due to location of the object

7. Measuring force of instrument

8. Error due to object surface finish

Types of Error

1. Alignment Error

2.Environmental Error

• These errors are caused due to surrounding

temperature, pressure, humidity, nuclear radiation,

vibration magnetic field

• To avoid error all metrology laboratories are maintain

at 20 degree Celsius.

3.Contact Error

Improper contact between measuring instrument and work piece

4. Parallax Error

• The position of the observer at thetime of taking reading can createerrors in measurement

5.Random error

These errors are caused due to

• Backlash and friction in the instruments

• Variation in position of setting work piece

• Displacement in joints of instruments

6.Systematic error (controllable error)

These errors includes

• calibration error

• Error due to ambient condition

• Error due to stylus pressure

7.Dirt error

• Presence of dirt in atmosphere may

change the reading by fraction.

• For greater accuracy, electronic

precipitators should be incorporated in

the lab.

Slip gauges• They are rectangular blocks of steel with

cross-section of 30x10 mm

• They can be used as reference standard, transferring dimension, for calibration and for direct measurement.

• They are supplied in set of 112 pieces to 32 pieces.

• Their faces are flat, parallel, has high degree of surface finish and accurately manufactured.

• Slip gauges are attached to each other by wringing process

Wringing

• Wringing is property of measuring faces of gauge block of adhering by sliding or pressing against each other.

Slip gauge set

• Principle – minimum slips

• Eg. 52.375mm

1.005+1.37+50=52.375

Exercise -73.975 mm

Linear measurement

1. Engineering steel rule

2. Calipers

3. Vernier caliper and its type

4. Micrometer and its type

1.Engineering steel rule

• Principle – comparison of unknown length with previously calibrated length

• Construction – strip of hardened steel with line graduations engraved at an interval of faction of standard unit of length.

• Accuracy – 0.5 mm

• Length of scale- 150,300,600,1000 mm

2.Calipers

• Principle- legs of the calipers are set against work piece, the distance between legs is transfer to scale.

Spring Caliper

3. Vernier caliper

• Principle – it uses two scales one fixed and other movable, then the difference these two scales can be utilized, to enhance the accuracy of measurement.

How to take reading?

• Total reading = main scale reading + (no. of division coinciding on vernierscale) X least count

• Least count = 𝑠𝑚𝑎𝑙𝑙𝑒𝑠𝑡 𝑑𝑖𝑣𝑖𝑠𝑖𝑜𝑛 𝑜𝑛 𝑚𝑎𝑖𝑛 𝑠𝑐𝑎𝑙𝑒

𝑡𝑜𝑡𝑎𝑙 𝑛𝑢𝑚𝑏𝑒𝑟 𝑜𝑓 𝑑𝑖𝑣𝑖𝑠𝑖𝑜𝑛𝑠 𝑜𝑛 𝑣𝑒𝑟𝑛𝑖𝑒𝑟 𝑠𝑐𝑎𝑙𝑒

• Total reading = 12 + 8 x 0.02 = 12.16 mm

Applications of vernier caliper

4.Vernier height gauge• Principle – it works on

same principle of verniercaliper

5.Vernier depth gauge• Principle – it works on same principle as that of

vernier caliper

6.Micrometer

• Principle – it works on the principle of movement of a nut and a screw

How to take reading?

7.Screw thread micrometer

• Principle – similar to simple micrometer

8.Inside micrometer

9.Depth micrometer

• Used for measurement of depth of holes, slots

Angular measurement

1. Sine bars

2. Sine center

3. Angle gauges

4. Auto-collimator

5. Angle dekkor

1.Sine bars

• Construction-

Working of sine bars

h L

Angle measurement for heavy components

Sine center

Advantages

• Accurate and precise

• Easily available

• Cheap

Disadvantage

• Application is limited

• Accurate upto 45 degree

• Difficult to hold in position

2.Angle gauge

• Angle gauges are the wedge shaped block and are used for angle measurement.

• These are 13 pieces, divided into 3 types

The first series angles are 1°,3°,9°,27°,41°

The second series angles are 1’,3’,9’,27’

The third series angles are 3”,6”,18”,30”

The angle gauges can be used for large number of combination by adding or subtraction of these gauges from each other

Addition of angle Subtraction of angle

For example, to measure 43°24’12”_______?

Applications of angle gauges

• Use of angle gauge (greater than 90°)

• Use of angle gauge (less than 90°)

3.Auto-collimator

• This is an optical instrument which is used for measuring small angular deviation.

• Working principle of auto-collimator

Collimating lens

Working of auto-collimator

4.Angle dekkor

Roundness

• Roundness is a condition of surface of revolution such as cylinder,cone or sphere where all points on surface intersected by any planeperpendicular to common axis or passing through a common centerare equidistant from the axis.

• Circularity is only in one plane, whereas roundness even includesthree dimensions such as in balls of ball bearing

The error of circularity at a cross section can be of following type

• Ovality – this errors occurs when there is a difference between the diameters.

• Error = maximum diameter – minimum diameter

• Lobbing –in this case, the diameter measured at any two position remains constant. Say D1 but still it is not exactly equal to the original diameter D.

• Irregularities of specific form- in this case, the variation in the diameter occurs due to irregular surface profile

Roundness measurement by polar graph

Error =𝑒𝑟𝑟𝑜𝑟 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑓𝑟𝑜𝑚 𝑡ℎ𝑒 𝑝𝑜𝑙𝑎𝑟 𝑔𝑟𝑎𝑝ℎ

𝑟

where r is the constant whose value depends on shape and work piece and angle of block

Calibration

• Calibration is the process of checking the accuracy ofmeasurement of an instrument or gauge by comparing it withthe measurement with similar instrument that has been certifiedas a standard of known accuracy.

• Calibrations directly links customer’s measuring instruments tonational or international standards.

• Calibrations means to find out weather the instrument givescorrect reading or not.

Standard procedure for calibration

1. Cleaning of instruments

2. Determination of error

3. Check for tolerable limits

4. Minor changes

5. Allotment of calibration set-up

6. Next calibration date

Example

1.Vernier caliper

Zero error

Flatness of measuring jaw

Parallelism of measuring jaw

Error in reading

Width of spherical inside measuring jaws

Example

2.Micrometer

Zero error

Flatness of measuring surface

Parallelism of measuring surface

Error in reading

Relative movement of moving parts

General appearance

Traceability • Traceability means that a measured result can be related to stated

reference, usually national or international standard through anunbroken chain of comparison, all having stated uncertainties.

• Traceability gives the user confidence that his/her measurementsagree with the national standards within the stated uncertainty.

• It also ensure that the measurements will be equivalent to thosemade using different instruments from different suppliers.

• This is particularly important when importing or exporting goods.