Introduction to Metrology

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Introduction To Introduction To Metrology Metrology

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Introduction to Metrology

Transcript of Introduction to Metrology

Page 1: Introduction to Metrology

Introduction To MetrologyIntroduction To Metrology

Page 2: Introduction to Metrology

Meaning of MetrologyMeaning of Metrology Metrology is the science of measurement. Metrology may be divided depending upon the quantity

to be measured like metrology of length, metrology of time.

But for engineering purposes, it is restricted to measurement of length and angles and other qualities which are expressed in linear or angular terms.

In the broader sense it is not limited to length measurement but is also concerned with industrial inspection and its various techniques.

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Metrology is mainly concerned with:

(1) Establishing the units of measurements, ensuring the uniformity of measurements.

(2) Developing methods of measurement.

(3) Errors of measurement.

(4) Accuracy of measuring instruments and their care.

(5) Industrial inspection and its various techniques.

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Legal MetrologyLegal Metrology

• Legal MetrologyLegal metrology is directed by a national organization which is called national service of Legal metrology. It includes a no. of international organization whose ultimate object is to maintain uniformity of measurement throughout the world.

• The activities of legal metrology are:(1) Control of measuring instruments.(2) Testing of prototype/models of measuring instruments.(3) Examination of measuring instrument to verify its conformity.

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• In design, design engineer should not only check his design from the point of view of the strength or economical production, but he should also keep in mind how the dimensions specified can be checked or measured.

• Higher productivity and accuracy can be achieved by properly understood, introduced the Metrology.

• You can improve the measuring accuracy and dimensional and geometrical accuracies of the product.

Necessity and importance of Necessity and importance of MetrologyMetrology

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• Proper gauges should be designed and used for rapid and effective inspection.

• Also automation and automatic control, which are the modern trends for future developments, are based on measurement. Digital instruments also we can used for inspection.

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Quality control – Metrology as a means Quality control – Metrology as a means to achieveto achieve

Whenever parts must be inspected in large numbers hundred percent inspection of each part is not only slow and costly but in addition does not eliminate all of the defective pieces.

Mass inspection tends to be careless, operators become fatigue and inspection gauge become worn or out of adjustment more frequently.

Quality control enables an inspector to sample the part being produced in a mathematical manner and to determine whether or not the entire stream of production is acceptable.

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• The following steps must be taken while using quality control techniques.

1) Sample the stream of product.

2) Measure the desired dimension.

3) Calculate the deviations of the dimensions from the mean dimension.

4) Construct a control chart.

5) Plot succeeding data on the control chart.

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Objectives of Metrology:Objectives of Metrology: The basic objective of a measurement is to The basic objective of a measurement is to

provide the required accuracy at a minimum provide the required accuracy at a minimum cost.cost.

1.1. Complete evaluationComplete evaluation of newly developed of newly developed products.products.

2.2. Determination of Determination of Process CapabilitiesProcess Capabilities..3.3. Determination of the measuring Determination of the measuring instrument instrument

capabilities capabilities and ensure that they are quite and ensure that they are quite sufficient for their respective measurements.sufficient for their respective measurements.

4.4. Minimising the Minimising the cost of inspectioncost of inspection by effective by effective and efficient use of available facilities.and efficient use of available facilities.

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5.5. Reducing the Reducing the cost of rejectscost of rejects and rework and rework through application of statistical quality control through application of statistical quality control techniques.techniques.

6.6. To standardiseTo standardise the measuring methods. the measuring methods.

7.7. ToTo maintain maintain the accuraciesthe accuracies of measurement. of measurement.

8.8. To To prepare designprepare design for all gauges and special for all gauges and special inspection fixtures.inspection fixtures.

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Process of measurement:Process of measurement:

• The sequence of operations necessary for The sequence of operations necessary for the execution of measurement is called the execution of measurement is called process of measurement.process of measurement.

• There are main three important elements There are main three important elements of measurement,of measurement,(1) (1) Measurand:Measurand:

- Measurand is the physical quantity - Measurand is the physical quantity or property like length, angle, diameter, or property like length, angle, diameter, thickness etc. to be measured. thickness etc. to be measured.

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Continue..Continue..(2) Reference:(2) Reference:

- It is the physical quantity or property to which - It is the physical quantity or property to which quantitative comparisons are made.quantitative comparisons are made.

(3) Comparator:(3) Comparator: - It is the means of comparing measuring measurand - It is the means of comparing measuring measurand with some reference.with some reference.

• Suppose a fitter has to measure the length of M.S. Suppose a fitter has to measure the length of M.S. plate- he first lays his rule along the flat. He then plate- he first lays his rule along the flat. He then carefully aligns the zero end of his rule with one end of carefully aligns the zero end of his rule with one end of M.S. flat and finally compares the length of M.S. flat M.S. flat and finally compares the length of M.S. flat with the graduations on his rule by his eyes. In this with the graduations on his rule by his eyes. In this example, the length of M.S. flat is a example, the length of M.S. flat is a measurandmeasurand, steel , steel rule is the rule is the referencereference and eye can be considered as a and eye can be considered as a comparatorcomparator. .

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Methods of Measurement:Methods of Measurement: The methods of measurement can be classified as:The methods of measurement can be classified as:

(1) Direct method:(1) Direct method:• This is a simple method of measurement, in which the value of This is a simple method of measurement, in which the value of

the quantity to be measured is obtained directly without the the quantity to be measured is obtained directly without the calculations.calculations.

• For example, measurements by scales, vernier callipers, For example, measurements by scales, vernier callipers, micrometers, bevel protector etc.micrometers, bevel protector etc.

• This method is most widely used in production. This method is This method is most widely used in production. This method is not very accurate because it depends on human judgment. not very accurate because it depends on human judgment.

(2) Indirect method:(2) Indirect method:• In indirect method the value of quantity to be measured is In indirect method the value of quantity to be measured is

obtained by measuring other quantities which are functionally obtained by measuring other quantities which are functionally related to required value.related to required value.

• for example, angle measurement by sine bar, measurement of for example, angle measurement by sine bar, measurement of shaft power by dynamometer etc.shaft power by dynamometer etc.

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Measuring system:Measuring system: A measuring system is made of five elements:A measuring system is made of five elements:

These are:These are:(1) Standard (1) Standard (2) Work piece(2) Work piece(3) Instrument(3) Instrument(4) Person(4) Person(5) Environment(5) Environment

- The most basic element of measurement is a standard without which no The most basic element of measurement is a standard without which no measurement is possible.measurement is possible.

- Once the standard is chosen select a work piece on which measurement Once the standard is chosen select a work piece on which measurement will be performed.will be performed.

- Then select a instrument with the help of which measurement will be Then select a instrument with the help of which measurement will be done.done.

- The measurement should be performed under standard environment. The measurement should be performed under standard environment. - And lastly there must be some person or mechanism to carry out the And lastly there must be some person or mechanism to carry out the

measurement.measurement.

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Accuracy:Accuracy:

• Accuracy is defined as the closeness of the Accuracy is defined as the closeness of the measured value with true value. measured value with true value.

OROR• Accuracy is defined as the degree to which the Accuracy is defined as the degree to which the

measured value agrees with the true value.measured value agrees with the true value.• Practically it is very difficult to measure the true Practically it is very difficult to measure the true

value and therefore a set of observations is value and therefore a set of observations is made whose mean value is taken as the true made whose mean value is taken as the true value of the quantity measured.value of the quantity measured.

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Precision:Precision:

• A measure of how close repeated trials are to each A measure of how close repeated trials are to each other.other. OR OR

• The closeness of repeated measurements.The closeness of repeated measurements.• Precision is the repeatability of the measuring process. It Precision is the repeatability of the measuring process. It

refers to the group of measurements for the same refers to the group of measurements for the same characteristics taken under identical conditions. characteristics taken under identical conditions.

• It indicated to what extent the identically performed It indicated to what extent the identically performed measurements agree with each other.measurements agree with each other.

• If the instrument is not precise it will give different results If the instrument is not precise it will give different results for the same dimension when measured again and for the same dimension when measured again and again.again.

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Distinction between Precision and Distinction between Precision and AccuracyAccuracy

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Figure shows the difference between the concepts of Figure shows the difference between the concepts of accuracy versus precision using a dartboard analogy that accuracy versus precision using a dartboard analogy that shows four different scenarios that contrast the two terms.shows four different scenarios that contrast the two terms.

A: Three darts hit the target center and are very close A: Three darts hit the target center and are very close together = high accuracy and precisiontogether = high accuracy and precision

B: Three darts hit the target center but are not very close B: Three darts hit the target center but are not very close together = high accuracy, low precisiontogether = high accuracy, low precision

C: Three darts do not hit the target center but are very C: Three darts do not hit the target center but are very close together = low accuracy, high precisionclose together = low accuracy, high precision

D: Three darts do not hit the target center and are not D: Three darts do not hit the target center and are not close together = low accuracy and precisionclose together = low accuracy and precision

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Factors affecting the accuracy of Factors affecting the accuracy of the measuring system:the measuring system:

• The basic components of an accuracy evolution The basic components of an accuracy evolution are the five elements of a measuring system are the five elements of a measuring system such as:such as:1. Factors affecting the calibration 1. Factors affecting the calibration standards.standards.2. Factors affecting the work piece.2. Factors affecting the work piece.3.3. Factors affecting the inherent Factors affecting the inherent characteristics of the instrument.characteristics of the instrument.4. Factors affecting the person, who carries out 4. Factors affecting the person, who carries out

the measurements. the measurements. 5. Factors affecting the environment.5. Factors affecting the environment.

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1. Factors affecting the standard. It may be affecting by:1. Factors affecting the standard. It may be affecting by:- Coefficient of thermal expansion,- Coefficient of thermal expansion,- calibration internal- calibration internal- stability with time- stability with time- elastic properties- elastic properties- geometric compatibility- geometric compatibility

2. Factors affecting the work piece, these are2. Factors affecting the work piece, these are- cleanliness, surface finish, surface defects etc.- cleanliness, surface finish, surface defects etc.- elastic properties- elastic properties- hidden properties- hidden properties- arrangement of supporting workpiece.- arrangement of supporting workpiece.

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3 .Factors affecting the inherent characteristics of 3 .Factors affecting the inherent characteristics of instrument.instrument.- Scale error- Scale error- effect of friction, hysteresis, zero drift- effect of friction, hysteresis, zero drift- calibration errors- calibration errors- repeatability and readability- repeatability and readability- constant geometry for both workpiece - constant geometry for both workpiece and and standardstandard

4. Factors affecting person:4. Factors affecting person:- training skill- training skill- ability to select the measuring instruments and standard- ability to select the measuring instruments and standard- attitude towards personal accuracy achievements- attitude towards personal accuracy achievements- sense of precision appreciation- sense of precision appreciation

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Continue..Continue..5. Factors affecting environment:5. Factors affecting environment:

- temperature, humidity etc.- temperature, humidity etc.- clean surrounding and minimum vibration enhance precision- clean surrounding and minimum vibration enhance precision- temperature equalization between standard, workpiece and - temperature equalization between standard, workpiece and instrument,instrument,- thermal expansion effects due to heat radiation from lights, - thermal expansion effects due to heat radiation from lights, heating elements, sunlight and people.heating elements, sunlight and people.

The above analysis of five basic metrology elements can be The above analysis of five basic metrology elements can be composed into the acronym.composed into the acronym.

SWIPE for convenient referenceSWIPE for convenient referenceWhere, S- standardWhere, S- standard

W- WorkpieceW- Workpiece I- InstrumentI- InstrumentP- PersonP- PersonE- EnvironmentE- Environment

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Sensitivity:Sensitivity:• Sensitivity may be defined as the rate of Sensitivity may be defined as the rate of

displacement of the indicating device of an displacement of the indicating device of an instrument, with respect to the measured instrument, with respect to the measured quantity.quantity.

• Sensitivity of thermometer means that it is Sensitivity of thermometer means that it is the length of increase of the liquid per the length of increase of the liquid per degree rise in temperature. More sensitive degree rise in temperature. More sensitive means more noticeable expansion. means more noticeable expansion.

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• In other words, sensitivity of an instrument In other words, sensitivity of an instrument is the ratio of scale spacing to the scale is the ratio of scale spacing to the scale division value. For example, if on a dial division value. For example, if on a dial indicator, the scale spacing is 1 mm and indicator, the scale spacing is 1 mm and the scale division value is 0.01 mm then the scale division value is 0.01 mm then sensitivity is 100. It is also called as sensitivity is 100. It is also called as amplification factor or gearing ratio.amplification factor or gearing ratio.

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Readability:Readability:• Readability refers to the ease with which Readability refers to the ease with which

the readings of a measuring instrument the readings of a measuring instrument can be read. can be read.

• Fine and widely spaced graduation lines Fine and widely spaced graduation lines improve the readability.improve the readability.

• To make the micrometers more readable To make the micrometers more readable they are provided with venier scale or they are provided with venier scale or magnifying devices.magnifying devices.

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Calibration:Calibration:• The calibration of any measuring The calibration of any measuring

instrument is necessary to measure the instrument is necessary to measure the quantity in terms of standard unit.quantity in terms of standard unit.

• It is carried out by making adjustments It is carried out by making adjustments such that the read out device produces such that the read out device produces zero output for zero input.zero output for zero input.

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• The process whereby the magnitude of the The process whereby the magnitude of the output of a measuring instrument is related to output of a measuring instrument is related to the magnitude of the input force driving the the magnitude of the input force driving the instrument (i.e. Adjusting a weight scale to zero instrument (i.e. Adjusting a weight scale to zero when there is nothing on it).when there is nothing on it).

• The accuracy of the instrument depends on the The accuracy of the instrument depends on the calibration.calibration.

• If the output of the measuring instrument is If the output of the measuring instrument is linear and repeatable, it can be easily linear and repeatable, it can be easily calibrated.calibrated.

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Magnification:Magnification:

• Magnification is the process of enlarging Magnification is the process of enlarging something only in appearance, not in something only in appearance, not in physical size so that it is more readable.physical size so that it is more readable.

(The stamp appears larger with the use of a magnifying glass.)

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Repeatability:Repeatability:• It is the ability of the measuring instrument to repeat the It is the ability of the measuring instrument to repeat the

same results for the measurements for the same same results for the measurements for the same quantity, when the measurements are carried outquantity, when the measurements are carried out- by the same observer,- by the same observer,- with the same instrument,- with the same instrument,- under the same conditions,- under the same conditions,- without any change in location,- without any change in location,- without change in the method of measurement,- without change in the method of measurement,- the measurements are carried out in short intervals of - the measurements are carried out in short intervals of time.time.

• It may be expressed in terms of dispersion of the results.It may be expressed in terms of dispersion of the results.

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Reproducibility:Reproducibility:

• Reproducibility is the closeness of the Reproducibility is the closeness of the agreement between the results of agreement between the results of measurements of the same quantity, when measurements of the same quantity, when individual measurements are carried out:individual measurements are carried out:- by different observers,- by different observers,- by different methods,- by different methods,- using different instruments,- using different instruments,- under different conditions, locations, times etc.- under different conditions, locations, times etc.

• It may be expressed in terms of the dispersion of It may be expressed in terms of the dispersion of the results.the results.

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Backlash:Backlash:

• In In Mechanical EngineeringMechanical Engineering, , backlashbacklash, is , is clearance between mating components, clearance between mating components, sometimes described as the amount of sometimes described as the amount of lost motion due to clearance or slackness lost motion due to clearance or slackness when movement is reversed and contact is when movement is reversed and contact is re-established. re-established.

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Hysteresis:Hysteresis:

• It is the difference between the indications It is the difference between the indications of a measuring instrument when the same of a measuring instrument when the same value of measured quantity is reached by value of measured quantity is reached by increasing or decreasing that quantity.increasing or decreasing that quantity.

• It is caused by friction, slack motion in the It is caused by friction, slack motion in the bearings and gears, elastic deformation, bearings and gears, elastic deformation, magnetic and thermal effects.magnetic and thermal effects.

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Drift:Drift:

• It is an undesirable gradual deviation of the It is an undesirable gradual deviation of the instrument output over a period of time that is instrument output over a period of time that is unrelated to changes in input operating unrelated to changes in input operating conditions or load.conditions or load.

• An instrument is said to have no drift if is An instrument is said to have no drift if is reproduces the same readings at different times reproduces the same readings at different times for same variation in measured quantity.for same variation in measured quantity.

• It is caused by wear and tear, high stress It is caused by wear and tear, high stress developed at some parts etc.developed at some parts etc.

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Threshold:Threshold:

• The min. value below which no output The min. value below which no output change can be detected when the input of change can be detected when the input of an instrument is increased gradually from an instrument is increased gradually from zero is called the threshold of the zero is called the threshold of the instrument. instrument.

• Threshold may be caused by backlash.Threshold may be caused by backlash.

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Resolution:Resolution:

• When the input is slowly increased from some When the input is slowly increased from some non-zero value, it is observed that the output non-zero value, it is observed that the output does not change at all until a certain increment does not change at all until a certain increment is exceeded; this increment is called resolution.is exceeded; this increment is called resolution.

• It is the min. change in measured variable which It is the min. change in measured variable which produces an effective response of the produces an effective response of the instrument.instrument.

• It may be expressed in units of measured It may be expressed in units of measured variablevariable

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Dead zone and Dead Time:Dead zone and Dead Time:

Dead Zone:Dead Zone:• The largest change of input quantity for which The largest change of input quantity for which

there is no change of output of the instrument is there is no change of output of the instrument is termed as dead zone.termed as dead zone.

• It may occur due to friction in the instrument It may occur due to friction in the instrument which does not allow the pointer to move till which does not allow the pointer to move till sufficient driving force is developed to overcome sufficient driving force is developed to overcome the friction loss.the friction loss.

• Dead zone caused by backlash and hysteresis Dead zone caused by backlash and hysteresis in the instrument.in the instrument.

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Dead Time:Dead Time:• The time required by a measurement The time required by a measurement

system to begin to respond to a change in system to begin to respond to a change in the measurand is termed as dead time.the measurand is termed as dead time.

• It represents the time before the It represents the time before the instrument begins to respond after the instrument begins to respond after the measured quantity has been changed.measured quantity has been changed.

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Errors in measurements:Errors in measurements:

• It is never possible to measure the true value It is never possible to measure the true value of a dimension, there is always some error.of a dimension, there is always some error.

• The error in the measurement is the The error in the measurement is the difference between the measured value and difference between the measured value and the true value of measured dimensions.the true value of measured dimensions.

• The error in measurement may be expressed The error in measurement may be expressed either as on absolute error or as a relative either as on absolute error or as a relative error.error.

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Absolute error:Absolute error:- True absolute error: It is the algebraic True absolute error: It is the algebraic

difference between the result of measurement difference between the result of measurement and the conventional true value of the quantity.and the conventional true value of the quantity.

- Apparent absolute error: If the series of - Apparent absolute error: If the series of measurement are made then the algebraic measurement are made then the algebraic difference between one of the results of difference between one of the results of measurement and the arithmetical mean is measurement and the arithmetical mean is known as apparent absolute error.known as apparent absolute error.

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Relative error:Relative error:- It is the quotient of absolute error and the It is the quotient of absolute error and the

true value or the arithmetical mean for true value or the arithmetical mean for series of measurement.series of measurement.

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Types of errors:Types of errors: During measurement several types of error may During measurement several types of error may

arise, these are:arise, these are:1. Static errors which includes:1. Static errors which includes:

(a) Reading errors(a) Reading errors(b) Characteristic errors(b) Characteristic errors(c) Environmental errors(c) Environmental errors

2. Instrumental loading errors.2. Instrumental loading errors.3. Dynamic errors.3. Dynamic errors.

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Continue…Continue…1.Static errors:1.Static errors:

- These errors result from the physical nature - These errors result from the physical nature of various components of measuring system. of various components of measuring system. There are three basic sources of static errors:There are three basic sources of static errors:

(a) (a) Reading errors:Reading errors:

- These errors occur due to carelessness of - These errors occur due to carelessness of operators. These do not have any direct operators. These do not have any direct relationship with other types of errors within relationship with other types of errors within the measuring system. the measuring system.

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Reading errors include:Reading errors include: Parallax error:Parallax error:

parallax errors arise on account of pointer and parallax errors arise on account of pointer and scale not being in same plane, we can eliminate scale not being in same plane, we can eliminate this error by having the pointer and scale in this error by having the pointer and scale in same plane.same plane.

Wrong scale reading and wrong recording of Wrong scale reading and wrong recording of data.data.

Inaccurate estimates of average reading.Inaccurate estimates of average reading. Incorrect conversion of units in calculationsIncorrect conversion of units in calculations ..

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(b) (b) Characteristics error:Characteristics error: It is defined as the deviation of the It is defined as the deviation of the

output of the measuring system from the output of the measuring system from the theoretical predicated performance or from theoretical predicated performance or from nominal performance specifications.nominal performance specifications.

Linearity errors, repeatability, hysteresis Linearity errors, repeatability, hysteresis are the characteristics errors if theoretical are the characteristics errors if theoretical output is straight line. Calibration error is output is straight line. Calibration error is also included in characteristics error.also included in characteristics error.

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(c) (c) Environmental errors:Environmental errors: These error result from the effect of These error result from the effect of

surrounding such as temperature, surrounding such as temperature, pressure, humidity etc. on measuring pressure, humidity etc. on measuring system.system.

It can be reduced by controlling the It can be reduced by controlling the atmosphere according to the specific atmosphere according to the specific requirement.requirement.

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2. 2. Instrument loading error:Instrument loading error: Loading errors results from the change in Loading errors results from the change in

measurand itself when being measured.measurand itself when being measured. Instrument loading error is the difference Instrument loading error is the difference

between the value of measurand before and between the value of measurand before and after the measurement.after the measurement.

For example a soft or ductile component is For example a soft or ductile component is subjected to deformation during measurement subjected to deformation during measurement due to the contact pressure of the instrument due to the contact pressure of the instrument and cause a loading error. The effect of this and cause a loading error. The effect of this error is unavoidable. error is unavoidable.

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3. 3. Dynamic errors:Dynamic errors: Dynamic error, also called measurement Dynamic error, also called measurement

error, is the difference between the true error, is the difference between the true value of measuring quantity and value value of measuring quantity and value indicated by measurement system if no indicated by measurement system if no static error is assumed. static error is assumed.

These errors can be broadly classified as:These errors can be broadly classified as:

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Continue…Continue…(a) Systematic or controllable errors:(a) Systematic or controllable errors:

- These errors are controllable in both their - These errors are controllable in both their magnitude and stress. These can also be magnitude and stress. These can also be determined and reduced. These are due to:determined and reduced. These are due to:

(1) Calibrations errors:(1) Calibrations errors:

- The actual length of standards such as - The actual length of standards such as scales will vary from nominal value by small scales will vary from nominal value by small amount. This will cause an error in amount. This will cause an error in measurement of constant magnitude. measurement of constant magnitude.

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(2) Atmospheric error:(2) Atmospheric error:

- Variation in atmospheric condition (i.e - Variation in atmospheric condition (i.e temperature, pressure and moisture temperature, pressure and moisture content) at the place of measurement from content) at the place of measurement from that of internationally agreed standard that of internationally agreed standard values (20’ temp. and 760 mm of Hg values (20’ temp. and 760 mm of Hg pressure) can give rise to error in pressure) can give rise to error in measurand size of the component. measurand size of the component.

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(3) Stylus pressure:(3) Stylus pressure:- Another common source of error is the - Another common source of error is the pressure with which the workpiece is pressed pressure with which the workpiece is pressed while measuring. Though the pressure involved while measuring. Though the pressure involved is generally small but this is sufficient enough to is generally small but this is sufficient enough to cause appreciable deformation of both the stylus cause appreciable deformation of both the stylus and the workpiece.and the workpiece.-Variations in force applied by the anvils of -Variations in force applied by the anvils of micrometer on the work to be measured results micrometer on the work to be measured results in the difference in its readings. In this case error in the difference in its readings. In this case error is caused by the distortion of both micrometer is caused by the distortion of both micrometer frame and workpiece.frame and workpiece.

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(4) Avoidable errors:(4) Avoidable errors:

- These errors may occur due to parallax, - These errors may occur due to parallax, non alignment of workpiece centers, non alignment of workpiece centers, improper location of measuring improper location of measuring instruments such as a thermometer in instruments such as a thermometer in sunlight while measuring temperature.sunlight while measuring temperature.

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Continue…Continue…(b) Random errors:(b) Random errors:

- The random errors occur randomly and the - The random errors occur randomly and the specific causes of such errors cannot be specific causes of such errors cannot be determined. The likely sources of this type of determined. The likely sources of this type of error are:error are:• Small variations in the position of setting Small variations in the position of setting

standard and workpiece.standard and workpiece.• Slight displacement of lever joints in the measuring Slight displacement of lever joints in the measuring

instrument.instrument.• Friction in measuring system.Friction in measuring system.• Operator errors in reading scale.Operator errors in reading scale.

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Difference between Systematic and Random Difference between Systematic and Random errors:errors:

Systematic errorSystematic error- These errors are These errors are

repetitive in nature repetitive in nature and are of constant & and are of constant & similar form.similar form.

- These errors result These errors result from improper from improper conditions.conditions.

Random errorRandom error- These are non These are non

consistent. The consistent. The sources giving rise to sources giving rise to such errors are such errors are random.random.

- Such errors are Such errors are inherent in the inherent in the measuring system.measuring system.

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- Expect personal Expect personal errors all other errors all other systematic errors can systematic errors can be controlled in be controlled in magnitude and sense.magnitude and sense.

- If properly analyzed If properly analyzed these can be these can be determined and determined and reduced or reduced or eliminated.eliminated.

- Specific causes, Specific causes, magnitudes and magnitudes and sense of these errors sense of these errors cannot be determined cannot be determined from the knowledge of from the knowledge of measuring system.measuring system.

- These errors cannot These errors cannot be eliminated, but the be eliminated, but the results obtained can results obtained can be corrected.be corrected.

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- These errors includes These errors includes calibration errors, calibration errors, variation in atmosphere, variation in atmosphere, pressure, misalignment pressure, misalignment error etc.error etc.

- These errors includes These errors includes Small variations in the Small variations in the position of setting position of setting standard and workpiece, standard and workpiece, Slight displacement of Slight displacement of lever joints in the lever joints in the measuring instrument, measuring instrument, Friction in measuring Friction in measuring system, Operator errors system, Operator errors in reading scale.in reading scale.