Introduction to Engineering Metrology :
What is Metrology?
Metrology is defined as the Science of Measurement. Concerned knowledge in measurement and includes both theoretical and practical problems related to measurement. It is used to enforce, validation, and verification to predefined standards. Metrology is a term which is derived from the Greek word "Metrologia" which means measure.
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(Speedometer) |
Types of Metrology
- Scientific Metrology
- Industrial Metrology
- Legal Metrology
Scientific Metrology
Industrial Metrology
Legal Metrology
Measurement
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(Manometer) |
Methods of Measurements
- Direct method
- Indirect method
Direct Method of Measurement
Indirect Method of Measurement
Levels of Measurement
- Primary Measurement
- Secondary Measurement
- Tertiary Measurement
Primary Measurement:
Secondary Measurement:
Tertiary Measurement
Metrological Terminologies
Accuracy
Precision
ACCURACY | PRECISION |
Accuracy is a measure of correctness. | Precision is a measure of how much-defined information is given. |
The value is correct and free from error. | Exactness is applied |
Accuracy can be improved | Precision cannot be improved |
Depends on the person measuring | Depends on the tool measuring |
Accuracy = Mean value - True Value | Precision = Individual value - Arithmetic value |
If Accuracy means the following results may be obtained
| If Precision means the following results may be obtained
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(High accuracy & low precision) |
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(High accuracy & high precision) |
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(Low accuracy & high precision) |
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(Low accuracy & low precision) |
Sensitivity
Repeatability
Reproducibility
Readability
Response time
Resolution
Stability
Calibration
Confirmation
Correction
Range
Span
Drift
- Temperature Variation.
- Wear and tear.
- Stray electric and Magnetic fields
- High mechanical stress created in some parts of instruments and systems
- Mechanical vibrations
- Zero drift
- Span drift
- Zonal drift
- Systematic Errors
- Random errors
- Gross errors
Hysteresis
- Hysteresis is the phenomenon defined as the difference outputs while loading and unloading.
- Hysteresis takes place due to the fact that all the energy put into the stressed part when loading is not recoverable while unloading.
- The output at particular input while increasing and decreasing varies because of internal friction or hysteresis damping.
Linearity
- Linearity is defined as the ability of an instrument to produce its input linearly.
- The closeness of the calibration curve to a specified straight line.