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1、Lesson 2.5 Actuators,Topics covered in this unit are as follows: The valve actuator (阀门执行器) The valve positioner (阀门定位器) The electric Motor actuators(电动执行器) Flow control actuators (流量控制执行器) and valve characteristics,1,Actuators,Operation of the closed-loop control system depends on the performance o
2、f 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. Each of these elements requires an actuator that will make the necessary conversion from controller output signal to element input.,
3、2,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。,每一个元件需要一个执行器，实现从控制器输出信号到元件输入的必要转化。,Actuators,This controller output may be pneumatic or electric and in some cases hydraulic or mechanical. The first need, then, is a device, an actuator, that will convert this control signal into a force th
4、at will position the final control element. From economic and performance standpoints, the most popular final operator is the pneumatic diaphragm actuator. A typical actuator is shown in Figure 2.5.1.,3,这种控制器输出可能是气动的或电动的，某些情况下是液压的或是机械的。,于是，首先需要的是一种装置，一种执行器，把这种控制信号转化成力，为终端控制原件定位。,Actuators,4,Actuator
5、s,5,Actuators,6,Actuators,7,1. Valve Actuator,The pneumatic signal is applied to a large flexible (柔性的) diaphragm backed by a rigid diaphragm plate. The force created is opposed by a coil (螺旋) spring (弹簧) with fixed spring rate. Thus, the stem position is an equilibrium of forces that depends on dia
6、phragm area, pneumatic pressure, and spring characteristic.,8,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。,产生的力对应于一个带有固定弹性比率的螺旋弹簧。,因此，（膜片刚性板）主干的位置点是一个力的平衡点，取决于膜面积、气压和弹簧特性。,1. Valve Actuator,The spring tension is adjusted to compensate for line pressure on the valve and to produce a full valve stroke with signa
7、l changes from bottom to top scale value. The mechanical designs employed vary from one manufacturer to another. Figure 2.5.1 illustrates the Foxboro Series actuator.,9,调整弹簧张力，使其补偿阀门的管线压力，使阀门产生满额冲程，即信号从最低值到最高值。,不同的生产制造商采用的机械设计是不同的。图2.5.1给出的是Foxboro系列执行器。,1. Valve Actuator,Pneumatic spring-diaphragm
8、actuators have many applications, the most common of which is the operation of a control valve. They have been adapted to globe, Saunders-patent, butterfly, and ball valves. Spring-diaphragm actuators convert air signal pressure to force and motion and can be adapted to a large number of industrial
9、requirements when precise loading of positioning is required.,10,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操纵。,它们适用于球心阀、桑托斯专利阀，蝶阀和球阀。,1. Valve Actuator,On loss of air signal, the spring will cause the actuator to return to the zero pressure position. This feature provides fail-safe action. First, in order to p
10、rovide maximum safety, the function of the valve is determined. Second, the actionair-to-open or air-to-closethat will allow the spring to put the valve in that position if the energy supply (air pressure) should fail is selected. The actuator shown can be reversed for either air-to-open or air-to-c
11、lose action by simply removing the cap, turning over the actuator, and replacing the cap.,11,在没有空气信号的情况下，弹簧会使执行器返回到零压力的位置。,这个特性为阀门在故障情况下提供了安全保障。首先，为了提供最大限度的安全保障，需要确定阀门的功能。,其次，在没有能量来源（即没有空气压力）情况下，气开式或气闭式的动作将会利用弹簧作用，使阀门达到合适的位置。,1. Valve Actuator,The motion of the valve stem positioned by a diaphragm a
12、ctuator is not exactly linear for uniform changes in air pressure (pneumatic signal). The nonlinearity is caused by the diaphragm material, variations in spring rate, the moving pieces, and packing box friction. (Packing box (密封盒) friction varies with fluid pressure and the type and compression of p
13、acking.),12,阀杆运动通过薄膜执行器进行定位，而该运动与均匀变化的气压并不是完全线性的关系。,这种非线性是由薄膜材料，弹簧率变化，部件移位以及密封盒摩擦力引起的（密封盒摩擦随着流体压力和它的型号以及密封材料压缩的变化而变化）。,1. Valve Actuator,One of the effects of friction and nonlinear diaphragm characteristics is hysteresis (迟滞，滞后现象). This is the difference between position on increasing versus positi
14、on on decreasing pneumatic signal pressure. With compression on the packing and fluid pressure on the valve, the hysteresis could possible be as high as 10 percent of the total travel.,13,摩擦力和非线性薄膜特性的影响之一是滞后现象。,这是由于增减气动压力信号而引起的位置增减变化不同。,1. Valve Actuator,In control applicatioins with low-gain or hig
15、h-proportional band, hysteresis can produce an insensitive area or dead zone in the control loop. This would make precise control difficult. The solution to this problem is (1) good design of the actuator; (2) careful choice of low-friction packing, such as Teflon rings (聚四氧乙烯填圈); (3) use of a valve
16、 positioner.,14,在低增益或高比例带的控制应用中，迟滞能够在控制回路中产生不灵敏区或者死区。,这将使精确控制变得困难。这个问题的解决办法是（1）设计良好的执行器；,2. Valve Positioner,If the diaphragm actuator does not supply sufficient force to position the valve accurately and overcome any opposition that flowing conditions create a positioner may be required. If the change in controller air pressure is small, the change in force available to reposition the valve stem might be too small to reposition it accurately.,15,如果薄膜执行器无法提供足够的作用力来精确定位阀门和克服任何反作用，那么就需要流量条件来产生一个
