chapter 8 mem371 metrology
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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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