电容式传感器中英文翻译资料（毕业设计用）.doc

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1、外文翻译Capacitive Sensor Operation Part 1: The BasicsPart 1 of this two-part article reviews the concepts and theory of capacitive sensing to help to optimize capacitive sensor performance. Part 2 of this article will discuss how to put these concepts to work.Noncontact capacitive sensors measure the c

2、hanges in an electrical property called capacitance. Capacitance describes how two conductive objects with a space between them respond to a voltage difference applied to them. A voltage applied to the conductors creates an electric field between them, causing positive and negative charges to collec

3、t on each objectCapacitive sensors use an alternating voltage that causes the charges to continually reverse their positions. The movement of the charges creates an alternating electric current that is detected by the sensor. The amount of current flow is determined by the capacitance, and the capac

4、itance is determined by the surface area and proximity of the conductive objects. Larger and closer objects cause greater current than smaller and more distant objects. Capacitance is also affected by the type of nonconductive material in the gap between the objects. Technically speaking, the capaci

5、tance is directly proportional to the surface area of the objects and the dielectric constant of the material between them, and inversely proportional to the distance between them as shown.:In typical capacitive sensing applications, the probe or sensor is one of the conductive objects and the targe

6、t object is the other. (Using capacitive sensors to sense plastics and other insulators will be discussed in the second part of this article.) The sizes of the sensor and the target are assumed to be constant, as is the material between them. Therefore, any change in capacitance is a result of a cha

7、nge in the distance between the probe and the target. The electronics are calibrated to generate specific voltage changes for corresponding changes in capacitance. These voltages are scaled to represent specific changes in distance. The amount of voltage change for a given amount of distance change

8、is called the sensitivity. A common sensitivity setting is 1.0 V/100 m. That means that for every 100 m change in distance, the output voltage changes exactly 1.0 V. With this calibration, a 2 V change in the output means that the target has moved 200 m relative to the probe.Focusing the Electric Fi

9、eldWhen a voltage is applied to a conductor, the electric field emanates from every surface. In a capacitive sensor, the sensing voltage is applied to the sensing area of the probe. For accurate measurements, the electric field from the sensing area needs to be contained within the space between the

10、 probe and the target. If the electric field is allowed to spread to other itemsor other areas on the targetthen a change in the position of the other item will be measured as a change in the position of the target. A technique called guarding is used to prevent this from happening. To create a guar

11、d, the back and sides of the sensing area are surrounded by another conductor that is kept at the same voltage as the sensing area itself. When the voltage is applied to the sensing area, a separate circuit applies the exact same voltage to the guard. Because there is no difference in voltage betwee

12、n the sensing area and the guard, there is no electric field between them. Any other conductors beside or behind the probe form an electric field with the guard instead of with the sensing area. Only the unguarded front of the sensing area is allowed to form an electric field with the target.Definit

13、ionsSensitivity indicates how much the output voltage changes as a result of a change in the gap between the target and the probe. A common sensitivity is 1 V/0.1 mm. This means that for every 0.1 mm of change in the gap, the output voltage will change 1 V. When the output voltage is plotted against

14、 the gap size, the slope of the line is the sensitivity. A systems sensitivity is set during calibration. When sensitivity deviates from the ideal value this is called sensitivity error, gain error, or scaling error. Since sensitivity is the slope of a line, sensitivity error is usually presented as

15、 a percentage of slope, a comparison of the ideal slope with the actual slope.Offset error occurs when a constant value is added to the output voltage of the system. Capacitive gauging systems are usually zeroed during setup, eliminating any offset deviations from the original calibration. However,

16、should the offset error change after the system is zeroed, error will be introduced into the measurement. Temperature change is the primary factor in offset error.Sensitivity can vary slightly between any two points of data. The accumulated effect of this variation is called linearity erro. The line

17、arity specification is the measurement of how far the output varies from a straight line.To calculate the linearity error, calibration data are compared to the straight line that would best fit the points. This straight reference line is calculated from the calibration data using least squares fitti

18、ng. The amount of error at the point on the calibration line furthest away from this ideal line is the linearity error. Linearity error is usually expressed in terms of percent of full scale (%/F.S.). If the error at the worst point is 0.001 mm and the full scale range of the calibration is 1 mm, th

19、e linearity error will be 0.1%.Note that linearity error does not account for errors in sensitivity. It is only a measure of the straightness of the line rather than the slope of the line. A system with gross sensitivity errors can still be very linear.Error band accounts for the combination of line

20、arity and sensitivity errors. It is the measurement of the worst-case absolute error in the calibrated range. The error band is calculated by comparing the output voltages at specific gaps to their expected value. The worst-case error from this comparison is listed as the systems error band. In Figu

21、re 7, the worst-case error occurs for a 0.50 mm gap and the error band (in bold) is 0.010.Gap (mm)Expected Value (VDC)Actual Value VDC)Error (mm)0.5010.0009.8000.0100.755.0004.9000.0051.000.0000.0000.0001.255.0005.0000.0001.5010.00010.1000.005Figure 7. Error valuesBandwidth is defined as the frequen

22、cy at which the output falls to 3 dB, a frequency that is also called the cutoff frequency. A 3 dB drop in the signal level is an approximately 30% decrease. With a 15 kHz bandwidth, a change of 1 V at low frequency will only produce a 0.7 V change at 15 kHz. Wide-bandwidth sensors can sense high-fr

23、equency motion and provide fast-responding outputs to maximize the phase margin when used in servo-control feedback systems; however, lower-bandwidth sensors will have reduced output noise which means higher resolution. Some sensors provide selectable bandwidth to maximize either resolution or respo

24、nse time.Resolution is defined as the smallest reliable measurement that a system can make. The resolution of a measurement system must be better than the final accuracy the measurement requires. If you need to know a measurement within 0.02 m, then the resolution of the measurement system must be b

25、etter than 0.02 m.The primary determining factor of resolution is electrical noise. Electrical noise appears in the output voltage causing small instantaneous errors in the output. Even when the probe/target gap is perfectly constant, the output voltage of the driver has some small but measurable am

26、ount of noise that would seem to indicate that the gap is changing. This noise is inherent in electronic components and can be minimized, but never eliminated.If a driver has an output noise of 0.002 V with a sensitivity of 10 V/1 mm, then it has an output noise of 0.000,2 mm (0.2 m). This means tha

27、t at any instant in time, the output could have an error of 0.2 m.The amount of noise in the output is directly related to bandwidth. Generally speaking, noise is distributed over a wide range of frequencies. If the higher frequencies are filtered before the output, the result is less noise and bett

28、er resolution (Figures 8, 9). When examining resolution specifications, it is critical to know at what bandwidth the specifications apply.Capacitive Sensor Operation Part 2: System OptimizationPart 2 of this two-part article focuses on how to optimize the performance of your capacitive sensor, and t

29、o understand how target material, shape, and size will affect the sensors response.Effects of Target SizeThe target size is a primary consideration when selecting a probe for a specific application. When the sensing electric field is focused by guarding, it creates a slightly conical field that is a

30、 projection of the sensing area. The minimum target diameter is usually 130% of the diameter of the sensing area. The further the probe is from the target, the larger the minimum target size.Range of MeasurementThe range in which a probe is useful is a function of the size of the sensing area. The g

31、reater the area, the larger the range. Because the driver electronics are designed for a certain amount of capacitance at the probe, a smaller probe must be considerably closer to the target to achieve the desired amount of capacitance. In general, the maximum gap at which a probe is useful is appro

32、ximately 40% of the sensing area diameter. Typical calibrations usually keep the gap to a value considerably less than this. Although the electronics are adjustable during calibration, there is a limit to the range of adjustment.Multiple Channel SensingFrequently, a target is measured simultaneously

33、 by multiple probes. Because the system measures a changing electric field, the excitation voltagefor each probe must be synchronized or the probes will interfere with each other. If they were not synchronized, one probe would be trying to increase the electric field while another was trying to decr

34、ease it; the result would be a false reading. Driver electronics can be configured as masters or slaves; the master sets the synchronization for the slaves in multichannel systems.Effects of Target MaterialThe sensing electric field is seeking a conductive surface. Provided that the target is a cond

35、uctor, capacitive sensors are not affected by the specific target material; they will measure all conductorsbrass, steel, aluminum, or salt wateras the same. Because the sensing electric field stops at the surface of the conductor, target thickness does not affect the measurement中文翻译电容式传感器操作第一部分：基础这

36、篇文章的第一部分回顾了电容式传感器的概念和理论来帮助我们优化电容式传感器的性能。第二部分讨论了怎样使这些概念去工作。 非接触式电容传感器测量的电特性变化称为电容。电容描述了有一定距离的两个导电物体怎样产生一个电压差。电压施加到导体上并产生电场，造成正负电荷聚集到每个导体上。如果电压的极性是相反的，那么电荷也是相反的。电容式传感器使用交流电压就会引起电子不断反转他们的位置。传感器就能检测出电子移动所产生的交流电流。电流的流量是由电容决定的，而电容是有导体的表面积和导体之间的距离决定的。表面积更大，距离更近的导体比小面积远距离导体能够引起更大的电流。导体之间介质的材料也影响电容。从技术上讲，电容是

37、与导体的表面积和在导体之间介质的介电常数成正比的，与导体之间的距离成反比。公式如下：在典型的电容式传感应用，探针或传感器是导体中的一个，另一个则是测量对象。（利用电容式传感器来感应塑料和其他绝缘体将在本文的第二部分讨论。）传感器和被测对象的大小假定不变，这是由他们之间的材料确定。因此，电容的任何改变都是探针和目标之间的距离变化产生的。被校准的电子产生特定的电压变化电容也产生相应变化。这些电压变化是与距离变化成比例的。在给定距离上产生的电压变化叫做灵敏度。一个常见的灵敏度设置时1.0 V/100 m。这就意味着每改变100m的距离，输出就会变化1V。有了这个校准，一个2V的输出变化就意味着目标距

38、离探测器发生了200m的变化。 关于电场 当电压应用于导体，电场从每个表面产生。在电容传感器中，感应电压应用到探头的感应区为了准确测量，感应区的电场需包含在探针与目标的空间内。如果电场可以传播到其他项目，或者目标的其他地区-在其他项目上这个位置的改变作为衡量在目标的这个位置上测量的变化。一种名为“守卫”的技术是用来防止这种情况发生。要创建一个守卫，感应区背部和四周都是被另一个导体包围，以使这个感应区本身为同一电压。当电压施加到感应区，一个单独的电路应用于完全相同的电压给守卫。因为在感应区和守卫之间没有电压差，所以在他们之间就没有电场。在探针周围或后面的导体能与守卫形成电场，而不是和感应区。只有

39、无守卫的感应区允许和目标形成电场。定义灵敏度表示在目标和探头之间的差距变化时，输出电压的变化。一个常用灵敏度单位是1 V/0.1 mm。这意味着距离每改变0.1mm，输出电压改变1V。以距离为行坐标输出电压为纵坐标描点，这条线的斜率就是灵敏度。在校准时，就设置系统的灵敏度。当灵敏度偏离理想值，这是所谓的灵敏度误差，增益误差，缩放错误。由于灵敏度是一个直线的斜率，灵敏度错误通常是表现为一个百分比的斜坡，一对理想与实际斜率的比较。偏移误差发生时，常值被添加到系统的输出电压。在设置期间电容测量系统通常是“零”，从原来的校准中解决了偏移误差。但是在系统清零后，偏移误差应当改变，误差将被引入到测量。温度

40、的变化是偏移误差的主要因素。灵敏度能够在数据的任何两点之间变化。这一变化的累积效应被称为线性误差。线性度规范是测量输出结果偏离直线多远。 为了计算线性误差，标定数据与最适合这些点的直线相比。这参考线是采用最小二乘拟合数据计算出的。校准线上的误差点中离基准线最远的点是线性误差。线性误差通常在百分之方面表示满量程（/ FS）的。如果在最低点误差为0.001毫米，全面的校准范围为 1毫米，线性误差为0.1。 请注意，线性误差不算到灵敏度误差中。这仅仅是该行的直线度测量，而不是直线的斜率。一个有着严重灵敏度错误的系统仍然可以非常好的线性的。 误差带是线性和灵敏度误差的组合。这是在校准测量范围内最坏的情

41、况下测量的绝对误差。该误差带的计算方法是比较在输出电压和他们的预期值的具体差距。从这个比较最坏情况的错误被列为该系统的误差带。在图7中，最坏的情况下误差为0.50毫米的差距和误差带（粗体）是-0.010。间隔 (mm)预期值(VDC)实际指标 (VDC)误差 (mm)0.5010.0009.8000.0100.755.0004.9000.0051.000.0000.0000.0001.255.0005.0000.0001.5010.00010.1000.005图7：误差值带宽的定义是，当输出频率下降至-3分贝的频率，这也是所谓的截止频率。一个在信号水平-3分贝下降，是近30的跌幅。与15 kH

42、z的带宽，为1V的低频率的变化，只会在15千赫0.7V的变化。宽的带宽传感器可以感知高频移动，并提供快速响应，在使用反馈的伺服控制系统中以最大限度地输出相位裕度；但是，低带宽的传感器会减少输出噪声，这意味着更高的分辨率。有些传感器提供可选择的带宽，以最大限度地提高或分辨率或响应时间。 分辨率是定义为一个系统可以做到最小的可靠的测量。一个测量系统的分辨率必须大于最终精确度的测量要求。如果您需要知道在0.02微米内的尺寸，则该测量系统的分辨率必须比0.02微米好。 分辨率的主要决定因素是电气噪声。电噪声出现在输出电压引起很小的输出误差。即使当探针/目标距离是完全不变，驱动器的输出电压具有小但可测量

43、的噪音，似乎就表明，这一距离在改变。这种噪声是电子元器件固有的，可以最小化，但从来没有消除。 如果一个驱动程序有一个为10V/1毫米的灵敏度为0.002 V的输出噪声，那么它的输出噪声0.000,2毫米（0.2微米）。这意味着，在经过一段时间后的任何瞬间，输出能有0.2微米的误差。对噪声的输出量对带宽有直接关系。一般来说，噪声的频率分布广泛。如果更高频率的输出前过滤，其结果是减少噪音和高分辨率（图8,9）。在检查分辨率时，关键是知道规格适用在什么带宽。电容式传感器操作第二部分：系统优化这部分分为这篇文章的第二部分着重就如何优化您的电容式传感器的性能，并了解靶材料，形状和大小如何影响传感器的响应

44、。 目标大小的影响当选择一个探测器进行特定的应用时，目标的大小是一个主要的考虑因素。当守卫关注感应电场时，它创建一个轻微的锥形场这是一个敏感领域的投影。最低目标的直径通常是感应区直径130。探头离目标越远，最小目标的大小越大。 测量范围 该范围是在其中一个探测器是一种有用的感应区大小的函数。面积越大，范围越大。由于电子产品的驱动程序在探头中被设计成有固定的电容，探头越小越应当靠近目标；来获得设计的电容量。一般来说，在其中一个有用的探测器中最大的距离大约是感应区域面积直径的40%。典型的校准通常保持对一个值大大低于这一标准的间距。虽然电子产品在校准时可调节的，但是有一个对调整范围的限制。 多通道

45、遥感通常情况下，目标是同时被多个探头测量。由于系统测量不断变化的电场，每个探头激励电压必须同步或探针会互相干扰。如果他们不同步，一个探头将努力增加电场，另一个则试图减少它，其结果将是一个错误的读数。电子驱动器可以被配置为主或副，主系统为副系统设置了多通道同步系统。 目标材料的影响该感应电场正在寻求一个导电表面。只要目标是一个导体，电容传感器不会受到目标材料影响，他们会衡量所有导线，如黄铜，钢，铝，或咸水作为相同。由于感应电场在导体表面停止，目标厚度不影响测量。 测量非导体 电容式传感器是最经常被用来衡量在导电目标位置的变化。但电容式传感器可以有效测量存在，密度，厚度以及非导体的位置。非导电材料，如塑料比空气有不同的电介质常数。介电常数决定两个导体之间不导电材料如何影响电容。当一个非导体插入探头和一个固定的参考指标之间，感应场穿过材料到接地目标。该非导电材料的出现改变介电常数，因此改变电容。电容会鉴于材料的密度或厚度而改变。