ENGINEERING METROLOGY | BASIC CONCEPTS OF MEASUREMENTS | METHODS | TERMS OF MEASUREMENT

This course is designed to provide a complete overview of the basic concepts and terminology of engineering metrology, including the fundamental principles of error sources, measurement uncertainty, and the principles of engineering metrology.

Engineering Metrology

Engineering Metrology is the science of measurement. It is also referred to as precision mechanics, and relates to the inspection of manufactured parts and processes. The field grew out of the industrial revolution when parts required consistency in order to function properly. The main benefits of engineering metrology are:

1. The production of high quality products
2. Reduced scrap rates
3. Cost savings through improved efficiency

Basic Concepts of Measurement

Measurements are essential for successful data analysis. Measurements are used to find patterns, trends and other relationships in the data. Measurements are important in all branches of science. The dictionary defines measurement as “the act or manner of determining the magnitude of something”. So, essentially, measurements are used to quantify some characteristic or feature of a given object under study. This is often done by comparing it with some other standard value of the same property. For example, you can compare the weight of an apple with that of a banana to determine which weighs more. You can also measure how much iron there is in different kinds

MEASUREMENTS

A Measurement is the outcome of an opinion formed by observers about some physical quantity.

Classification of measurements:

• Standards: ( Reproduce the value of a given quantity )
• Fixed Gauges (Check Dimensions)
• Measuring Instruments—(Determine the measured value)

Needs for measurement

1. To Determine the true dimensions of a part.

2. To increase our knowledge and understanding of the world.

4. To convert physical parameters into meaningful numbers.

5. To test if the elements that constitute the system function as per the design.

6. For evaluating the performance of a system.

7. For studying some basic laws of nature.

8. To ensure interchangeability with a view to promoting mass production.

9. To evaluate the response of the system to particular point.

10. To check the limitations of theory in actual situations.

11. To establish the validity of design and for finding new data and new designs.

Methods of Measurement

1. Direct Comparison

2. Indirect Comparison

3. Comparative Method

4. Coincidence Method

5. Fundamental Method

6. Contact Method

7. Transposition Method

8. Complementary Method

9. Deflection Method

Direct Method:

Measurements are directly obtained.

Ex:Vernier Caliper,Scales.

Indirect Method:

Obtained by measuring other quantities.

Ex:Diameter measurement by using three wires.

Comparative Method:

It’s compared with other known values.

Ex: Comparators.

Coincidence Method:

Measurements coincide with certain lines and signals.

Fundamental Method:

Measuring a quantity directly in relation to the definition of that quantity.

Contact Method:

Sensor/Measuring tip touches the surface area.

Ex: Vernier Caliper.

Transposition Method:

The quantity to be measured is first balanced by a known value and then balanced by another new known value.

Ex: Determination of mass by balancing methods.

Complementary Method:

The value of the quantity to be measured is combined with the known value of the same quantity.

Ex: Volume determination by liquid displacement.

Deflection Method:

The value to be measured is directly indicated by a deflection of the pointer.

Ex: Pressure Measurement.

Terms of Measurement

Precision:

The ability of the instrument to reproduce it’s readings or observation again and again for constant input signal.

Accuracy:

Closeness/conformity to the true value of the quantity under measurement.

Error:

The difference between true value and measured value is known as measurement error.

Error = Vt – Vm

Reliability:

It is defined as the probability that a given system will perform it’s function adequately for it’s specified period of lifetime under specified operating conditions.

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