MEM 371

METROLOGY

Chapter 8 : Errors in Measurement

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MEM 371 Metrology / Chapter 8: Errors in Measurement

Created by : NORASIKIN HUSSIN UiTMPP

• Calamitous/catastrophic error

• Alignment error

• Errors due to ambient condition

• Errors due to elastic deformation

Type of Errors

Error which

can be

eliminated

Error which

cannot be

eliminated

• Scale error

• Reading error

• Measuring error

MEM 371 Metrology / Chapter 8: Errors in Measurement

Created by : NORASIKIN HUSSIN UiTMPP

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Types of Errors

CAN BE AVOIDED

Calamitous or

catastrophic Errors

Alignment Errors

Errors due to ambient condition

Errors due to elastic

deformation

CANNOT BE ELIMINATED

Scale ErrorsReading Errors

Classifications & Types of Errors

MEM 371 Metrology / Chapter 8: Errors in Measurement

Created by : NORASIKIN HUSSIN UiTMPP

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Types of Errors which Can Be Eliminated

MEM 371 Metrology / Chapter 8: Errors in Measurement

Created by : NORASIKIN HUSSIN UiTMPP

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Types of Errors which Can Be Eliminated

MEM 371 Metrology / Chapter 8: Errors in Measurement

Created by : NORASIKIN HUSSIN UiTMPP

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Types of Errors which Can Be Eliminated

MEM 371 Metrology / Chapter 8: Errors in Measurement

Created by : NORASIKIN HUSSIN UiTMPP

1. Reading error

How accurate can a scale be read?

Guidelines• A reading of a pointer/datum line against a scale

divisions can be taken having an accuracy of the ± 10% of the scale divisions

Error which Cannot be Eliminated

Thickness on the ruling

The spacing of the scale divisions

Thickness of the datum/pointer

MEM 371 Metrology / Chapter 8: Errors in Measurement

Created by : NORASIKIN HUSSIN UiTMPP

• The estimate of the position of a pointer between the ruling will be less accurate ± 20% of the scale divisions

• Example : -a) Reading of -5 units taken off a scale whose divisions

represent 0.001 mm

b) reading had been of -3.4 scale units

Comparative measurement Accuracy det.

MEM 371 Metrology / Chapter 8: Errors in Measurement

Created by : NORASIKIN HUSSIN UiTMPP

Question

A plain Plug Gauge with nominal diameter 25 mm is measured using a comparator having a magnification of 5000x which is set to a gauge block of nominal length 25 mm having a known error of – 0.0001 mm to an accuracy determination ± 0.0002 mm. The comparator reading on the gauge block is 0 scale divisions and on the plug gauge is -1.2 scale divisions. What is the dimension of the plug gauge?

MEM 371 Metrology / Chapter 8: Errors in Measurement

Created by : NORASIKIN HUSSIN UiTMPP

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Measuring Errors

MEM 371 Metrology / Chapter 8: Errors in Measurement

Created by : NORASIKIN HUSSIN UiTMPP

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Compound Errors

MEM 371 Metrology / Chapter 8: Errors in Measurement

Created by : NORASIKIN HUSSIN UiTMPP

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Types of Errors which Can Be Eliminated

MEM 371 Metrology / Chapter 8: Errors in Measurement

Created by : NORASIKIN HUSSIN UiTMPP

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Calibration

Calibration

• Calibration is authentication of the accuracy lineage of any measurement tracing it back to the absolute standard. The other metrological and functional features at each step simply help the job done.

Traceability

• Meaning of the word: all measures is ranked according to [National Standard – High (Calibration/Reference) Standard – Low (Working) Standard] Formation as to control the measurement’s reliability and standard.

• Trace flow

MEM 371 Metrology / Chapter 8: Errors in Measurement

Created by : NORASIKIN HUSSIN UiTMPP

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