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1、电子信息类专业英语,http:/,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 Two Measurement Methods,1. What measurement methods are most important for measurement technology? 2. On what principles are the most important measurement methods developed based?,机械工业出版社 http:/,Passage Two Measurement Methods,Words and Expressio
2、ns deflection n. 偏转 null n. 零 compensation n. 补偿 auxiliary a. 辅助的,Passage Two Measurement Methods,Text In order to conduct measurements in an optimal fashion, it is essential to be familiar with the most important methods, principles of measurement. 1. Deflection methods, different method and null m
3、ethod With the deflection method the read-out of the measurement device used entirely determines the result of the measurement. The difference method measures (indicates) only the difference between the unknown quantity and the known, reference quantity. Here, the result of the measurement is partia
4、lly determined by the read-out of the measurement device used and partially by the reference quantity. Finally, with the null method the result is entirely determined by a known reference quantity. The read-out of the measurement instrument is used only to adjust the reference quantity to exactly th
5、e same value as the unknown quantity. The indication is then zero and the instrument is therefore used as a null detector or a zero indicator.,Passage Two Measurement Methods,2. Compensation methods On the basis of the number of power sources involved in a measurement, two other methods can be seen.
6、 The compensation method is a method of measurement that removes the effect of the unknown quantity on the measurements system by compensating it with the effect of a known quantity. This is done in such a way that the unknown quantity is no longer influenced by the measurement system when full comp
7、ensation is reached. If the unknown effect is compensated completely, no power is supplied to or withdrawn from the unknown quantity; the unknown quantity is not loaded by the measurement. The degree of compensation can be determined with a null indicator. The compensation method therefore requires
8、an auxiliary power source that can supply precisely the power that otherwise would have been withdrawn from the measured quantity. Thus, for the compensation method, we need two power sources.,Passage Two Measurement Methods,3. Analogy method This method makes use of a model of the object from which
9、 we wish to obtain measurement information. Measurements made on the model then provide information about the unknown object, as long as the model corresponds with the object in certain essential points. The analogy method is most often used when measurements of the actual object are not possible, e
10、xtremely difficult, time consuming or costly.,Passage Two Measurement Methods,4. Repetition method With this method several measurements of the same unknown quantity are conducted, each according to a different procedure. Most fundamental physical constants have been measured in several different wa
11、ys, to prevent the possibility of making the same (systematic) errors, specific to a certain type of measurement. Different (correctly applied) methods of measurement will produce similar results, but the measurement errors in the results will be independent of each other. This will yield an indicat
12、ion of the reliability of the measurement.,Passage Two Measurement Methods,Enumeration method The enumeration method is a method for determining the ratio of the magnitudes of two quantities (the known and unknown) by counting. Only numbers of objects, patterns or events can be counted. Physical qua
13、ntities of a given physical dimension must be measured. Measurement involves making errors, counting does not (mistakes excluded). The enumeration method is used, for instance, for measuring frequency. The frequency of a periodical signal is measured by simply counting the number of periods which fa
14、ll within an accurately determined reference time interval.,Passage Two Measurement Methods,Exercises . Match the items listed in the following two columns. 1. Deflection method a. 零值法 2. different method b. 偏转法 3. null method c. 指零仪 4. null detector /zero indicator d. 差值法,Passage Two Measurement Me
15、thods,. Complete the following sentences according to the text. 1. The result of the difference method measurement is partially determined by and partially by . 2. With the null method the result is entirely determined by . 3. The method is most often used when measurements of the actual object are not possible, extremely difficult, time consuming or costly. 4. The enumeration method is a method for determining the ratio of the magnitudes of two quantities (the known and unknown) by . Only , patterns or events can be counted.,Class is over!,Have a rest!,追 求,机械工业出版社 http:/www.cmpbook.c
