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Measurement




Unit 2

Measurement

Reading 1

This passage will introduce you to the principle of measurement in different fields of engineering. Look at the way it is divided into sections and paragraphs. Pay attention to the headings and to the table.

Task 1

Look at the questions and read the passage to find the answers. Remember, you do not have to understand every word.

1. Are engineering projects possible without knowledge of measurement?

2. How many types of temperature measurement are given in the third paragraph?

3. Do engineers need to know about all the different forms of measurement?

4. How many basic units is SI based on?

 

Measurement

Definition. A simple dictionary definition of the verb ‘to measure’ is: to find the size, quantity, volume, degree, weight, etc. of something by means of a standard or unit. In all branches of engineering, measurement plays a vital role since the design, manufacture and use of any product cannot be considered without reference to this concept. It is for this reason that the majority of texts on engineering contain tables, charts, lists or appendixes which provide the student with accepted standards and units of measurement.

 

Knowledge of measurement. We are all familiar with the symbols C and F for scales of temperature, but there is also K (Kelvin), which is the fraction (1/273.16) of the thermodynamic temperature of the triple part of water. Of course it may not always be necessary to understand the precise definition itself, provided one can understand the significance of the term or figure in relation to the diagram, chart or calculation involved. Each branch of engineering, naturally, tends to be more concerned with some particular forms of measurement than with others.

 

Conversion factors and SI equivalents. Look, for example, at Table 1 below, taken from a text for chemical engineers and which shows conversion factors. Then compare it with Table 2 which gives US customary units and their SI equivalents and comes from a text on sanitation engineering. At first glance it may seem difficult to find any connection between the two. However, if you look closely you will see that much of the information shown deals with the same things but from a different approach. Clearly, the students in either of the engineering branches would have little difficulty in using the figures and symbols relating to their own specialization.

 

SI Units. SI is the abbreviation for Systeme International d’Unites. SI is based on seven basic units, each of which is defined with great accuracy and from which all other basic units are derived. Under the system, each physical quantity has only one particular unit for its measurement. Thus, a length is only measured in metres. If the number employed with a basic unit is very small, or very large, then a prefix can be used as in km for kilometers. Conversion tables are necessary because the USA and Britain still retain a measurement system which is different from that used by the rest of the world.

 

Measuring devices. Since measurement is so important, it follows that there is a wide range of devices and instruments which are designed to indicate very precisely length, pressure, time and so on.

 

Task 2


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