测控专业英语Unit3

1、Unit 3 测控技术与仪器专业英语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 测量策略测量策略 Frequency spectrum 频谱频谱 coherent sampling 相关采样相关采样 periodic 周期的周期的 reconstructed signal 重现的信号重现的信号 random sampling 随机采样随机采样 nonlinearity 非线性非线性 systematic errors 系统误差系统误差 random errors 随机误差随机误差

4、 calibration 标定标定 response-time 响应时间响应时间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 采用采用偏转法偏转法测量时，测量时，测量设备的读数测量设备的读数完全决定了完全决定了测量的结果。测量的结果。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. 微差法微差法即是测量未知量与即是测量未知量与参考量参考量（已知量）之间（已知量）之间的差。故测量结果一部分取决于测量设备的读数，的差。故测量结果一部分取决于测量设备的读数，一部分取决于参考量。一部分取决于参考量。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，对于最后，对于零位法零位法，其测量结果完全取决于已知参，其测量结果完全取决于已知参考量。测量仪器的读数只是考量。测量仪器的读数只是使参考量与未知量准确使参考量与未知量准确一致一致。其显示值为。其显示值为0，故这种仪器被作为零值探测器，故这种仪器被作为零值探测器或零值指示器使用。或零值指示器使用。91 Measurement Methods(3) Analogy method 类推

9、法类推法 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. 这种方法利用待测对象的模型获取测量信息。这种方法利用待测对象的模型获取测量信息。只要模型只要模型在某些特定关键点上与对象相符，则测量可以对模型展在某些特定关键点上与对象相符，则测量可以对模型展开并可提供未知对象的信息。开并可提供未知对象的信息。这种方法适用于实际对象这种方法适用于实际对象测量不可能、极困难、耗时长或成本高的情况。测量不可能、极困难、耗时长或成本高的情况。101 Measureme

11、nt Methods(4) Repetition method 复测法复测法 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. 该方法即是对未知量进行若干次测量。大多数该方法即是对未知量进行若干次测量。大多数基基础物理常量础物理常量的测量都采用若干不同的方式，以防的测量都采用若干不同的方式，以防止出现相同（系统）误差，特别是对于某些特定止出现相同（系统）误差，特别是对于某些特定形式的测量。形式的测量。11Main content Measurement Methods1Measurement Strategies2Error, Accuracy and Precision3Systematic and Random Error4122 Measurement Strategies (1) Co

13、herent sampling 相关采样或相干采样相关采样或相干采样 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. 针对针对周期周期信号，该策略可以使我们能够利用信号，该策略可以使我们能够利用带宽带宽小于测量信号的测量系统处理该

14、信号。小于测量信号的测量系统处理该信号。132 Measurement Strategies (1) Coherent sampling 相关采样或相干采样相关采样或相干采样 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. 通过采用

15、比通过采用比n个信号周期略长的时间间隔对实际个信号周期略长的时间间隔对实际测量信号进行采样，信号的波形可以保存下来，测量信号进行采样，信号的波形可以保存下来，并可以真实地复现。并可以真实地复现。142 Measurement Strategies (1) Coherent sampling 相关采样或相干采样相关采样或相干采样 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. 复现信号，也就是采样峰值的复现信号，也就是采样峰值的包络线包络线，其频宽要，其频宽要小于处理该采样信号的测量系统的带宽。小于处理该采样信号的测量系统的带宽。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. 如果我们对幅值信息感兴趣，而非信号的波形，如果我们对幅值信息感兴趣，而非信号的波形，则采样可以发生在任意时刻，即则采样可以发生在任意时刻，即随机采样随机采样。在这。在这种策略下，很容易

18、确定宽种策略下，很容易确定宽频谱频谱信号的信号的均方根值均方根值。而且，信号不必一定是周期的。而且，信号不必一定是周期的。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. 除计数外，所有测量得到的都是真值的除计数外，所有测量得到的都是真值的近似近似值。值。误差即是某个量的真值或最好可接受值与测

20、量误差即是某个量的真值或最好可接受值与测量值之间的偏差。如果比较测量值和真值所得的值之间的偏差。如果比较测量值和真值所得的误差足够小，那么我们就认为测量足够误差足够小，那么我们就认为测量足够准确准确。1.4183 Error, Accuracy and Precision It is important for the user of an instrument to know what confidence can be placed in it. 了解仪器的了解仪器的可信度可信度对于使用者来说是非常重要对于使用者来说是非常重要的。的。 The number of digits used t

21、o describe a measured quantity is not always representative of the true accuracy of the measurement 用于表示被测量的数字位数不总是能够说明测用于表示被测量的数字位数不总是能够说明测量的真实量的真实准确性准确性。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 精确性精确性是指对某量的一些测量数据点的重复性是指对某量的一些测量数据点的重复性的量度。仪器精确性同时取决于其的量度。仪器精确性同时取决于其分辨率分辨率和和稳稳定性定性。 精确性：对同一物体的某特征重复观察值或对精确性：对同一物体的某特征重复观察值或对某参数的重复估计值彼此之间的接近程度。某参数的重复估计值彼此之间的接近程度。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 前续部分对分辨率的定义是仪器能够探测被测量的最小前续部分对分辨率的定义是仪器能够探测被测量的最小可辨别可辨别改变量。改变量。 Stability refers to freedom from random variations in the result 稳定性是指结果不受随机变量的干扰。稳定性是指结果不受随机变量的干扰。 Precision is a

24、measure of the dispersion of a set of data，not a measure of the accuracy of the data 精确性是数据集合分散程度的量度，而非数据准确性的精确性是数据集合分散程度的量度，而非数据准确性的量度。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 可能有的仪器因读数不可能有的仪器因读数不分散分散而具备精确性，但而具备精确性，但因系统误差造成它并不准确。反之，如果仪器因系统误差造成它并不准确。反之，如果仪器不具备精确性，则其不可能准确。不具备精确性，则其不可能准确。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 系统误差一直出现在相同的情况下。能导致系系统误差一直出现在相同的情况下。能导致系统误差的原因包括：不准确的统误差的原因包括：不准确的标定标定、不匹配的不匹配的阻抗阻抗、响应时间响应时间误差、非线性、设备误差、非线性、设备故障故障、环、环境改变和负载影响。境改变和负载影响。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. ) 系统误差通常是观测者未知的，并且其产生源并不系统误差通常是观测者未知的，并且其产生源并不在测量考虑范围内

29、。有时，系统误差是由于超出测在测量考虑范围内。有时，系统误差是由于超出测量范围误用仪器造成的，如使用量范围误用仪器造成的，如使用电压表电压表测量超出其测量超出其可测频率的电压量。（这也被称为可测频率的电压量。（这也被称为应用误差应用误差）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. 系统误差的另一种形式是系统误差的另一种形式是负载误差负载误差。当一个仪。当一个仪器接入器接入电路电路，它就成为待测电路的一部分，并，它就成为待测电路的一部分，并在某种程度上改变了原电路。在某种程度上改变了原电路。如果这部分影响如果这部分影响未予以考虑的话未予以考虑的话，那么，那么高阻抗高阻抗电路的测量结果电路的测量结果会受到严重的影响。会受到严重的影响。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