1、Unit 3 測控技術與儀器專業英語Measurement Methods and StrategiesChapter 1 Introduction to Measurement2 Q1 What measurement methods are most important for measurement technology? Q2 On what principles are the most important measurement methods developed based? Q3 What is the problem of measurement strategies bro

2、ught forward in addition to the measurement methods? Questions before reading除除之外之外3 Q4 What can one do with the help of the three strategies mentioned in the text individually? Q5 At what difficulties do these strategies have individually? Q6 What principles are these strategies based on and what i

3、mportant methods are used regarding each strategy? Questions before reading4 measurement strategy 測量策略測量策略 Frequency spectrum 頻譜頻譜 coherent sampling 相關采樣相關采樣 periodic 周期的周期的 reconstructed signal 重現的信號重現的信號 random sampling 隨機采樣隨機采樣 nonlinearity 非線性非線性 systematic errors 系統誤差系統誤差 random errors 隨機誤差隨機誤差

4、 calibration 標定標定 response-time 響應時間響應時間Words and Expressions5Main content Measurement Methods1Measurement Strategies2Error, Accuracy and Precision3Systematic and Random Error461 Measurement Methods(1) Deflection method, difference method and null method With the deflection method the read-out of th

5、e measurement device used entirely determines the result of the measurement 采用采用偏轉法偏轉法測量時，測量時，測量設備的讀數測量設備的讀數完全決定了完全決定了測量的結果。測量的結果。71 Measurement Methods(1) Deflection method, difference method and null method The difference method measures (indicates) only the difference between the unknown quantity

6、 and the known, reference quantity. Here, the result of the measurement is partially determined by the read-out of the measurement device used and partially by the reference quantity. 微差法微差法即是測量未知量與即是測量未知量與參考量參考量（已知量）之間（已知量）之間的差。故測量結果一部分取決于測量設備的讀數，的差。故測量結果一部分取決于測量設備的讀數，一部分取決于參考量。一部分取決于參考量。81 Measure

7、ment Methods(1) Deflection method, difference method and null method 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 the same value as the unknown quantit

8、y. The indication is then zero and the instrument is therefore used as a null detector or zero indicator. 最后，對于最后，對于零位法零位法，其測量結果完全取決于已知參，其測量結果完全取決于已知參考量。測量儀器的讀數只是考量。測量儀器的讀數只是使參考量與未知量準確使參考量與未知量準確一致一致。其顯示值為。其顯示值為0，故這種儀器被作為零值探測器，故這種儀器被作為零值探測器或零值指示器使用。或零值指示器使用。91 Measurement Methods(3) Analogy method 類推

9、法類推法 This method makes use of a model of the object from which 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. This method is most often used whe

10、n measurements of the actual object are not possible, extremely difficult, time consuming or costly. 這種方法利用待測對象的模型獲取測量信息。這種方法利用待測對象的模型獲取測量信息。只要模型只要模型在某些特定關鍵點上與對象相符，則測量可以對模型展在某些特定關鍵點上與對象相符，則測量可以對模型展開并可提供未知對象的信息。開并可提供未知對象的信息。這種方法適用于實際對象這種方法適用于實際對象測量不可能、極困難、耗時長或成本高的情況。測量不可能、極困難、耗時長或成本高的情況。101 Measureme

11、nt Methods(4) Repetition method 復測法復測法 With this method several measurements of the same unknown quantity are conducted. Most fundamental physical constants have been measured in several different ways, to prevent the possibility of making the same (systematic) errors, specific to a certain type of

12、measurement. 該方法即是對未知量進行若干次測量。大多數該方法即是對未知量進行若干次測量。大多數基基礎物理常量礎物理常量的測量都采用若干不同的方式，以防的測量都采用若干不同的方式，以防止出現相同（系統）誤差，特別是對于某些特定止出現相同（系統）誤差，特別是對于某些特定形式的測量。形式的測量。11Main content Measurement Methods1Measurement Strategies2Error, Accuracy and Precision3Systematic and Random Error4122 Measurement Strategies (1) Co

13、herent sampling 相關采樣或相干采樣相關采樣或相干采樣 This measurement strategy enables us to process a measurement signal with a spectrum width F, which is considerably larger than the bandwidth B of the measurement system, provided that the signal is periodic. 針對針對周期周期信號，該策略可以使我們能夠利用信號，該策略可以使我們能夠利用帶寬帶寬小于測量信號的測量系統處理該

14、信號。小于測量信號的測量系統處理該信號。132 Measurement Strategies (1) Coherent sampling 相關采樣或相干采樣相關采樣或相干采樣 By taking samples of the actual measurement signal at intervals that are just slightly larger than n periods of the signal, the shape of the signal can be preserved and a true representation can be obtained. 通過采用

15、比通過采用比n個信號周期略長的時間間隔對實際個信號周期略長的時間間隔對實際測量信號進行采樣，信號的波形可以保存下來，測量信號進行采樣，信號的波形可以保存下來，并可以真實地復現。并可以真實地復現。142 Measurement Strategies (1) Coherent sampling 相關采樣或相干采樣相關采樣或相干采樣 The reconstructed signal which is the envelope of the peaks of the samples, has a frequency spectrum which is smaller than the bandwidt

16、h of the measurement system used to process the sampled signal. 復現信號，也就是采樣峰值的復現信號，也就是采樣峰值的包絡線包絡線，其頻寬要，其頻寬要小于處理該采樣信號的測量系統的帶寬。小于處理該采樣信號的測量系統的帶寬。152 Measurement Strategies (2) Random sampling If we are only interested in amplitude informationhowever，and not in the shape of the signal, the samples can b

17、e taken at arbitrary moments：random sampling. In this manner it is very easy to determine, for example, the RMS-value of a signal with a wide frequency spectrum. The signal does not have to be periodic here. 如果我們對幅值信息感興趣，而非信號的波形，如果我們對幅值信息感興趣，而非信號的波形，則采樣可以發生在任意時刻，即則采樣可以發生在任意時刻，即隨機采樣隨機采樣。在這。在這種策略下，很容易

18、確定寬種策略下，很容易確定寬頻譜頻譜信號的信號的均方根值均方根值。而且，信號不必一定是周期的。而且，信號不必一定是周期的。16Main content Measurement Methods1Measurement Strategies2Error, Accuracy and Precision3Systematic and Random Error4173 Error, Accuracy and Precision All measurements that do not involve counting are approximations of the true value. Error

19、 is the difference between the true or best accepted value of some quantity and the measured value. A measurement is said to be accurate if the error is small-accuracy refers to a comparison of the measured and accepted, or “true,” value. 除計數外，所有測量得到的都是真值的除計數外，所有測量得到的都是真值的近似近似值。值。誤差即是某個量的真值或最好可接受值與測

20、量誤差即是某個量的真值或最好可接受值與測量值之間的偏差。如果比較測量值和真值所得的值之間的偏差。如果比較測量值和真值所得的誤差足夠小，那么我們就認為測量足夠誤差足夠小，那么我們就認為測量足夠準確準確。1.4183 Error, Accuracy and Precision It is important for the user of an instrument to know what confidence can be placed in it. 了解儀器的了解儀器的可信度可信度對于使用者來說是非常重要對于使用者來說是非常重要的。的。 The number of digits used t

21、o describe a measured quantity is not always representative of the true accuracy of the measurement 用于表示被測量的數字位數不總是能夠說明測用于表示被測量的數字位數不總是能夠說明測量的真實量的真實準確性準確性。1.81.11193 Error, Accuracy and Precision Precision is a measure of the repeatability of a series of data points taken in the measurement of some

22、quantity. The precision of an instrument depends on both its resolution and its stability 精確性精確性是指對某量的一些測量數據點的重復性是指對某量的一些測量數據點的重復性的量度。儀器精確性同時取決于其的量度。儀器精確性同時取決于其分辨率分辨率和和穩穩定性定性。 精確性：對同一物體的某特征重復觀察值或對精確性：對同一物體的某特征重復觀察值或對某參數的重復估計值彼此之間的接近程度。某參數的重復估計值彼此之間的接近程度。2.2203 Error, Accuracy and Precision Recall th

23、at resolution was defined in the previous section as the minimum discernible change in the measurand that can be detected 前續部分對分辨率的定義是儀器能夠探測被測量的最小前續部分對分辨率的定義是儀器能夠探測被測量的最小可辨別可辨別改變量。改變量。 Stability refers to freedom from random variations in the result 穩定性是指結果不受隨機變量的干擾。穩定性是指結果不受隨機變量的干擾。 Precision is a

24、measure of the dispersion of a set of data，not a measure of the accuracy of the data 精確性是數據集合分散程度的量度，而非數據準確性的精確性是數據集合分散程度的量度，而非數據準確性的量度。量度。2.42.7213 Error, Accuracy and Precision It is possible to have a precision instrument that provides readings that are not scattered but that are not accurate bec

25、ause of a systematic error. However，it is not possible to have an accurate instrument unless it is also precise 可能有的儀器因讀數不可能有的儀器因讀數不分散分散而具備精確性，但而具備精確性，但因系統誤差造成它并不準確。反之，如果儀器因系統誤差造成它并不準確。反之，如果儀器不具備精確性，則其不可能準確。不具備精確性，則其不可能準確。2.822Main content Measurement Methods1Measurement Strategies2Error, Accuracy a

26、nd Precision3Systematic and Random Error4234 Systematic and Random Error Systematic errors consistently appear in a measurement in the same direction. These could be caused by inaccurate calibration, mismatched impedances, response-time error, nonlinearities, equipment malfunction, environmental cha

27、nge, and loading effects 系統誤差一直出現在相同的情況下。能導致系系統誤差一直出現在相同的情況下。能導致系統誤差的原因包括：不準確的統誤差的原因包括：不準確的標定標定、不匹配的不匹配的阻抗阻抗、響應時間響應時間誤差、非線性、設備誤差、非線性、設備故障故障、環、環境改變和負載影響。境改變和負載影響。1.2244 Systematic and Random Error Systematic errors are often unknown to the observer and may arise from a source that was not considered

28、in the measurement. Sometimes a systematic error occurs because of the misuse of an instrument outside its design range，such as when a voltmeter is used to measure a frequency beyond its specifications(This is also called an applicational error. ) 系統誤差通常是觀測者未知的，并且其產生源并不系統誤差通常是觀測者未知的，并且其產生源并不在測量考慮范圍內

29、。有時，系統誤差是由于超出測在測量考慮范圍內。有時，系統誤差是由于超出測量范圍誤用儀器造成的，如使用量范圍誤用儀器造成的，如使用電壓表電壓表測量超出其測量超出其可測頻率的電壓量。（這也被稱為可測頻率的電壓量。（這也被稱為應用誤差應用誤差）1.4254 Systematic and Random Error Another common type of systematic error is loading error. Whenever an instrument is connected to a circuit, it becomes part of the circuit being m

30、easured and changes the circuit to some extent. Measurements in high-impedance circuits can be significantly affected if this is not taken into account. 系統誤差的另一種形式是系統誤差的另一種形式是負載誤差負載誤差。當一個儀。當一個儀器接入器接入電路電路，它就成為待測電路的一部分，并，它就成為待測電路的一部分，并在某種程度上改變了原電路。在某種程度上改變了原電路。如果這部分影響如果這部分影響未予以考慮的話未予以考慮的話，那么，那么高阻抗高阻抗電路的測量結果電路的測量結果會受到嚴重的影響。會受到嚴重的影響。1.8264 Systematic and Random Error Other systematic errors can occur because the calibration was performed under different environmental conditions than those present when the instrument is in ser