TC S361 Instrumentation and Testing Techniques (Free Courseware)

Measurement is a big part of our daily lives. You have to pay your water bill according to your monthly volume usage. If you are paid via an hourly rate, the company you work for will measure the working hours you have put in each day. When you fill your car with gasoline, it must be measured so you know how much you are expected to pay. You may want to know if the butcher stall gives you enough meat for the money you have paid. Similar measurement-related questions appear in the testing and certification industry. For example, are toys that may carry trace amounts of toxic elements safe for children? Are electrical products safe to use? And so on.

But when we are using an instrument to take a measurement, how can we be sure that the instrument is accurate or not? This is crucial when we are doing business with foreign countries, since both parties, i.e. suppliers and customers, must know about and agree upon the same measurement units and standards. These standards are needed to ensure that such trade is fair.

This module starts with an overview of the two important standards of measurement units: British standard and SI units. Concepts related to measurement traceability are then explained in the second section. This module should take you about six hours to complete, including the time you will need to complete the activities and self-tests.

Units of measurements

Before we look at units of measurement, let’s watch a short online video in Activity 1 (Page 2) that discusses the need for measurement. You learned in the module introduction that when we do business with foreign countries, both parties — the sellers and the customers — need to know and hold to the same measurement units and standards to make sure each trade is fair. Let’s begin, therefore, by taking a closer look at what those units are, and how they are used.

The International System of Units (SI units)

The International System of Units (SI units) is the most widely used unit system in science, engineering, and in our daily life. Please refer to the following online article for a brief history of SI units.

The SI units system has been adopted globally, except for in the United States, Liberia and Myanmar (Burma). Canada has adopted the SI units for all legal purposes, but imperial/US units (which will be discussed later in this section) are also still in use there. The United Kingdom has officially adopted SI units. 2 The Hong Kong official unit system is the SI unit system. You should find that the package of rice you have bought from supermarket shows the mass in kilograms. Because Hong Kong is a centre for international trade, keeping to the right standards is crucial here.