Measurement is the process of comparing unknown magnitude of certain parameter with the known predefined standard of that parameter. For the measurements results to be accurate, two conditions should be met.
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Scope of Measurement
Measurements are one of crucial parts of not only mechanical engineering but all types of engineering fields. Every branch of engineering involves two processes: design, and operations and maintenance. The design may be machine design, building design, circuit design, transportation design, automobile design etc. The operations part involves operation of the machines, automobiles, various plants, circuits etc.
Both, the design, and operations and maintenance involve measurements. For instance while designing automobile we have to consider dimensions of various parts of the automobiles, the loads they can pick up etc. Similarly during the operations of the plant, say like industrial refrigeration plant, we have to measure parameters like pressure, temperature, etc. In the power plant we have to measure various quantities of the coal, the quantity of water in the boiler, the amount of steam produced along with its flow rate, temperature and pressure, the amount of power produced, the outlet temperature of the steam from condenser etc. In the large chemical plants large number of such parameters have to be measured.
In the field of civil engineering, measurements play dominant role. Right from the initial process of designing and drawing, laying the lines, raising the foundation to the construction of walls, designing of structures, centering, and all the finishing works, large number of measurements are involved. There is hardly any stage in building construction, where we don’t need measurements.
Once Lord Kelvin said, “I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it, but when you cannot express it in numbers, your knowledge is of meager and unsatisfactory kind: it may be the beginning of knowledge, but you have scarcely in your thoughts, advanced to the stage of science, whatever the matter may be.”
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What is Measurement?
Measurement is the process of comparing unknown magnitude of certain parameter with the known predefined standard of that parameter. For instance, if we have to measure the temperature of the body, we measure it with the thermometer that has predefined scale indicating different values of the temperature. If we have to measure the length of the wall, we measure it with the measuring tape that has predefined markings on it. The measurement enables us obtaining magnitude of certain parameters whose value is not known by comparing them with the standards whose value is predefined.
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Requirements of Measurement
For the measurements results to be accurate, two conditions should be met. Firstly, the standard which is used for comparison must be defined accurately and it should be universally accepted. For instance the weight cannot be just light or heavy. It should be light or heavy in comparison to some standard weight and should be measured accurately against it. The comparison of the unknown magnitude should be made with the recognized standard and it should produce some meaningful reading of the value.
The second important condition to be met for measurements is that the procedure applied for the measurements should be provable and there should be provable instruments for measurements. This means the methods for making the measurements and the instruments used for them should be reliable enough to make the correct measurements.
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1) Book: Mechanical Measurements by Thomas G. Beckwith and N. Lewis Buck
What is Measurement? Methods of Measurement. General Measurement System.
This is the series of articles that describes what is measurement, methods of measurement, and the general measurement system. It describes the importance of the transducer in the measurement system along with an example of measuring pressure using Bourdon tube.