电子信息类专业英语,http:/www.cmpbook.com,机械工业出版社同名教材配套电子教案,温丹丽 高源 制作,Passage One Definition of Measurement,1. How to give a necessary and sufficient definition to measurement? 2. What a concept is the measurement established based on? 3. What condition can a definition of measurement be considered as a satisfying one?,机械工业出版社 http:/www.cmpbook.com,Passage One Definition of Measurement,Words and Expressions intuition () n. 直觉，直觉的知识 acquisition wz n. 获得，获得物 measurand n. 被测（物理）量 observation n. 观测 subjective a. 主观的 dip v. 浸，浸泡 magnetic a. 磁的，有磁性的 guarantee v. 保证 objectively ad. 客观地 intensity n. 强度，亮度 qualitative a. 定性的，性质上的,Passage One Definition of Measurement,Text A possible operational description of the term measurement which agrees with intuition is the following: “measurement is the acquisition of information”; the aspect of gathering information is one of the most essential aspects of measurement; measurements are ducted to learn about the object of measurement; the measurand. This means that a measurement must be descriptive with regard to that state or that phenomenon in the world around us which we are measuring. There must be a relationship between this state or phenomenon and the measurement result. Although the aspect of acquiring information is elementary, it is merely a necessary and not a sufficient aspect of measurement: when one reads a textbook, one gathers information, but one does not perform a measurement.,Passage One Definition of Measurement,A second aspect of measurement is that it must be selective. It may only provide information about what we wish to measure (the measurand) and not about any other of the many states or phenomena around us. This aspect too is a necessary but not sufficient aspect of measurement. Admiring a painting inside an otherwise empty room will provide information about only the painting, but does not constitute a measurement.,Passage One Definition of Measurement,A third and necessary aspect of measurement is that it must be objective. The outcome of the measurement must be independent of an arbitrary observer. Each observer must extract the same information from the measurement and must come to the same conclusion. This, however, is almost impossible for an observer who uses only his/her senses. Observations made with out senses are highly subjective. Our sense of temperature, for example, depends strongly on any sensation of hot or cold preceding the measurement. This is demonstrated by trying to determine the temperature of a jug of water by hand. If the hand is first dipped in cold water, the water in the jug will feel relatively warm, whereas if the hand is first dipped in cold water, the water in the jug will fell relatively cold.,Passage One Definition of Measurement,Besides the subjectivity of our observation, we human observers are also handicapped by the fact that there are many states or phenomena in the real world around us which we cannot observe at all (e.g. magnetic fields), or only poorly (e.g. extremely low temperatures or high-speed movement). In order to guarantee the objectivity of a measurement we must therefore use artifacts (tools or instruments). The task of these instruments is to convert the state or phenomenon under observation into a different state or phenomenon that cannot be misinterpreted by an observer. In order works, the instrument converts the initial observation into a representation that all observers can observe and will agree on. For the measurement instruments output, therefore, objectively observable output such as numbers on an alpha-numerical display should be used rather than subjective assessment of such things as colour, etc. Designing such instruments, which are referred to as measurement systems, is the field of (measurement) instrumentation.,Passage One Definition of Measurement,In the following, we will define measurement as the acquisition of information in the form of measurement results, concerning characteristics, states or phenomena (the measurand) of the world that surrounds us, observed with the aid of measurement systems (instruments). The measurement system in this context must guarantee the required descriptiveness, the selectivity and the objectivity of the measurements. We can distinguish two types of information: information on the state, structure or nature of certain characteristic, so-called structural information, and information on the magnitude, amplitude or intensity of certain characteristic, so-called metric information. The acquisition of structural information is called a qualitative measurement; the acquisition of metric information is called a quantitative measurement. If the nature of the characteristic to be measured is not (yet) known, it must be determined first by means of a qualitative measurem