shown in Figure 2.1.2(a). 膜片包含一个薄层或薄膜，支撑在一个刚性框架上，如图2.1.2(a). A silicon diaphragm uses silicon, which is a semiconductor (半导体). 硅膜片使用硅材料，也就是半导体材料.
Capsules are two diaphragms joined back to back, as shown in Figure 2.1.2(b). 膜盒是由两个膜片紧密连接，如图2.1.2(b).
Bellows are similar to capsules, except that the diaphragms instead of being joined directly together, are separated by a corrugated tube (波纹管) or tube with convolutions (旋转), as shown in Figure 2.1.2(c). 波纹管类似与膜盒，不同之处在于膜片不是直接连在一起，而是被一个波纹状的管或旋转的管分开，如图2.1.2(c)所示
Bourdon tubes are hollow (中空的), cross-sectional (横截面) beryllium (铍), copper (青铜), or steel tubes, shaped into a three quarter circle, as shown in Figure 2.1.5(a).
波登管是中空的，横截面是铍，青铜，或钢的，制作成四分之三圆周状，如图2.1.5(a)所示.
The tubes can also be shaped into helical (螺旋状的) or spiral (螺旋形的) shapes to increase their range.The Bourdon tube is normally used for measuring positive gauge pressures, but can also be used to measure negative gauge pressures.
管可以是螺旋状或螺旋形增大或减小.波登管农场用于测量正值表压，但是也可以用于测量负值表压. (helical: 螺旋状，spiral: 绕某一中心点不断靠近或远离) 2.2
This unit discusses the measurement of the level of liquids and free flowing (自由流动) solids in containers (容器). The detector is normally sensing the interface (界面) between a liquid and a gas, a solid and a liquid, or possibly the interface between two liquids. Sensing liquid levels fall into two categories; firstly, single-point sensing (单点检测) and secondly, continuous level monitoring (监测). In the case of single-point sensing the actual level of the material is detected when it reaches a predetermined (预定，预置) level, so that the appropriate action can be taken to prevent overflowing (溢出) or to refill (再充填) the container.
这一单元讨论容器内液体和自由流动固体的液面测量. 探测器通常检测液体和气体，固体和液体，或者两种液体之间的界面. 检测液体液面可分为两类：一类是单点检测，第二类是对连续液面进行监测.在单点检测的情况下，当物质的当前液面被检测出达到预定液面时，（控制器）采用适当的动作来防止溢出或再次填充容器.
Buoyancy (浮力) is an indirect method used to measure liquid levels. 浮力是一种测量液面的间接方法.
Capacitive probes (电容电极) can be used in nonconductive (非导电的) liquids and free flowing solids for level mesurement.
电容电极可以用于非导电液体和自由流动固体的液面测量.
Level Sensing Devices液面测量仪器 Direct Level Sensing液面直接测量（法） Sight glass (open end/differential) or gauge is the simplest method for direct visual reading.
玻璃液面计或玻璃液面表是最为简单的方法，可以直接视觉读取数据.
Conductive probes are used for single-point measurements in liquids that are conductive and nonvolatile as a spark (火花) can occur.
导电电极(传感器) 用于液位单点测量，液体是导电的并且不可挥发，防止电火花的产生.
Capacitive probes are used in liquids that are nonconductive and have a high μ and can be used for continuous level monitoring.
导电容电极用于不导电并且具有很高的介电常数μ的液体，可以用于连续液面监测.
Ultrasonics can be used for single point or continuous level measurement of a liquid or a solid. 超声波(传感器)可以用于液体或固体的单点液位测量或连续液位测量. 2.3
Velocity (速度) is a measure of speed and direction of an object. 速度是对一个物体速率和方向的测量.
Laminar flow (层流) of a liquid occurs when its average velocity is comparatively low and the fluid particles tend to move smoothly in layers, as shown in Figure 2.3.1(a).
层流发生在液体流速相对较低时，流体粒子在各层中倾向于平滑移动，如图2.3.1(a)所示.
Turbulent flow (湍流) occurs when the flow velocity is high and the particles no longer flow smoothly in layers and turbulence (紊乱) or a rolling (旋转，滚动) effect occurs.
湍流发生在液速较高，在各层中，粒子不在是平滑移动，而是产生紊乱或旋转.
Viscosity (粘度，粘性) is a property of a gas or liquid that is a measure of its resistance to motion or flow. A viscous (粘性的) liquid such as syrup (糖浆) has a much higher viscosity than water and water has a higher viscosity than air.
粘度是描述气体或液体对运动或流动的阻力的一种特性. 粘性的液体比如糖浆，其年度要远大于水，而水的粘度又高于空气.
Energy factors. Most flow equations are based on the law of energy conservation and relate the average fluid or gas velocity, pressure, and the height of fluid above a given reference point. This relationship is given by Bernoulli equation.
能量因素. 大多数流体方程基于能量守恒法，使液体或气体平均速度，压力，流体在给定参考点的高度联系起来. 这种关系由伯努利方程给出. 2.4
Thermoelectric effect sensors rely on the physical principle that, when any two different metals are connected together, an e.m.f., which is a function of the temperature, is generated at the junction between the metals. The general form of this relationship is:e=a1T+a2T2+a3T3+?+anTn Where e is the e.m.f. generated and T is the absolute temperature. 热电势效应传感器取决于物理原理，当任意两个不同的金属连接在一起时，将在金属的接头处产生感应电动势，是温度的函数。这个关系的一般形式是： 其中，e是感应电动势，T是绝对温度。
Wires of such pairs of materials are connected together at one end, and in this form are known as thermocouples. Thermocouples are a very important class of device as they provide the most commonly used method of measuring temperatures in industry.
这对材料的线一头连接起来，这种形式被认为是热电偶。热电偶是一种很重要的装置，因为它们为工业温度测量提供了最为普遍的方法。
The e.m.f. generated at the point where the different wires are connected together is represented by a voltage source, E1, and the point is known as the hot junction. The temperature of the hot junction is customarily shown as Th on the diagram. The e.m.f. generated at the hot junction is measured at the open ends of the thermocouple, which is known as the reference junction.
相连接处不同的导线所产生的感应电动势可以用电压源E1表示，该点为热结点。热结点的温度在图中以Th来表示。热结点产生的感应电动势可以在热电偶的开放末端测量，该点被看做参考连接点。 2.5
Operation of the closed-loop control system depends on the performance of each loop component, including the final control element, whether it be damper, variable speed pump (变速泵), motor relay (电动机继电器), saturable reactor (饱和电抗器), or valve.
闭环控制系统的运行取决于每一环节元件的性能，包括终端控制元件,、阻尼器、变速泵、电动机继电器、饱和电抗器或阀门。
The pneumatic signal is applied to a large flexible (柔性的) diaphragm backed by a rigid diaphragm plate.
气动信号施加于一个较大的、柔性的膜片上，膜片固定于一个刚性平板上。
Pneumatic spring-diaphragm actuators have many applications, the most common of which is the operation of a control valve.
气动弹簧薄膜式执行器可以应用于很多地方，最为普便的是控制阀门的应用。
One of the effects of friction and nonlinear diaphragm characteristics is hysteresis (迟滞，滞后现象).
摩擦的影响之一和薄膜的非线性特性是迟滞。
Positioners provide precise positioning and also increase the response speed of the valve. 产定位器提供了精确的定位，也提高了阀门的响应速度。
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