Engineering Metrology notes Unit 1.1

Unit 1 
1.1          Definition of Metrology, Objectives 
Important points: 
·              Need of measurement:
         Measurement is necessary for
1.     To know unknown physical quantity.
2.     To compare dimensions of components.
3.     To assure that the product is manufactured as per the drawing / specifications.
4.      To detect errors in manufacturing.

1.1 Definition of Metrology :
Metrology is defined as “science of measurement” which is concerned with methods of measurement based on agreed units and standards.

According to International Bureau of Weights and Means (BIPM) as “the science of measurement embracing both experiment and theoretical determinations measures at any level of uncertainty in the  field of science and technology”.

1.1.1   Objectives of Metrology :

1.      Selection of appropriate measurements instrument:

         There are various measuring parameters of product / components. Hence selection of proper                    instrument is necessary.
2.      Standardisation of measuring methods:
         To maintain uniformity of measurement, it is necessary to standardise measuring methods.
3.      To analyse new developed products:
         Metrology helps to check performance and measurement of important parameters of developed                product.
4.      To determine process capabilities:
         Metrology helps to determine process capabilities of machines.
5.      To minimise cost of inspection:
         Metrology helps to reduce cost of inspection through suitable tools and techniques economically.
6.      Design of special gauges / instruments:
         Metrology can be used to design special gauges /instruments which are difficult to measure.

1.1  Categories of Metrology: 

1.      Scientific metrology :

-           It establishes units of measurement, new methods of measurement, standards, etc.
-           It is related with the organization and development of measurement standards and with their                   maintenance at  highest level.
-           It is based on the scientific methods, rules and regulations for development of measurement                     process and standards.
-           It is involved with research and new technologies for government, healthcare industries, etc.
-           It is considered the top level of metrology which gives highest degree of accuracy.
2.      Industrial metrology :
-           It is related to measurement involved in industrial sector. It is concerned with instruments used in  a wide variety of industries are functioning properly.
        eg . Aircraft industry, manufacturing industry etc.
-           It involves design and development of measuring equipment, gauges which are used in industrial inspection.
-           It is important for nation¢s economical and industrial development.
3.      Legal metrology :
-           It is based on legal and technical requirement decided by the authority or government for units of measurement, methods of measurements and measuring instruments.
-           The International Organization for legal metrology was established to maintain 
      Standardisation along the lines of international standards.
-           Legal metrology is directed by various government or statutory organizations like.
        i)     National Service of Legal Metrology (NSLM)
        ii)    International Organization of Weights and Measures (IOWM)

4.      Deterministic metrology:

•  It is related to process measurement which is based on deterministic measurement.
• In deterministic measurement, the results of measurements can be determined on the basis of previous results on the basis of predictions using various types of or sensors and devices.
•  e.g. Automatic machines like CNC machines where process measurement is important and we can use automatic sensors to measure various parameters.

Review Questions: 

1. Define metrology - 2 Marks

2. List types of metrology-2 Marks

3. State objectives of metrology -4 Marks

4. Explain role of legal metrology- 4 Marks