机电-体化专业英语10

1、Introduction to Programmable Logic ControllerPart I Technical and Practical Reading Passage A Programmable Logic Controller (PLC) This section on programmable logic controllers illustrates just a small sample of their capabilities. As computers, PLCs can perform timing functions (for the equivalent

2、of time-delay relays), drum sequencing, and other advanced functions with far greater accuracy and reliability than what is possible to use electromechanical logic devices. Most PLCs have the capacity for far more than six inputs and six outputs. The following photograph shows several input and outp

3、ut modules of a single Allen-Bradley PLC (Fig. 1). With each module having sixteen points of either input or output, this PLC has the ability to monitor and control dozens of devices. Fit into a control cabinet, a PLC takes up little room, especially considering the equivalent space that would be ne

4、eded by electromechanical relays to perform the same functions (Fig. 2). One advantage of PLCs that simply cannot be duplicated by electromechanical relays is remote monitoring and control via digital computer networks. Because a PLC is nothing more than a special-purpose digital computer, it has th

5、e ability to communicate with other computers rather easily. The following photograph (Fig. 3) shows a personal computer displaying a graphic image of a real liquid-level process (a pumping station for a municipal wastewater treatment system) controlled by a PLC. The actual pumping station is locate

6、d miles away from the personal computer display. The characteristic structure of programmable logic controllers is illustrated in Fig. 4. Provision is made to accept information from various input switching devices such as push-buttons, limit switches, and relay contacts. Also provided are terminals

7、 to which output devices such as solenoids, relay coils, and indicator lights can be connected. There are no direct-wired connections between the inputs and outputs. Instead, the switched conditions of the inputs are converted to logic-level signals that are inputs to a digital computer in the contr

8、ol unit. A program stored in the computer specifies which outputs should be energized on the basis of the present and past states of the input signals. Logic-level outputs from the control unit are converted to the voltage levels required to energize or de-energize the various output devices. The PL

9、C software is comprised of the operating system, the basic software and the user program. The operating system contains all the statements and declarations for internal system functions. The basic software has a flexible interface to the operating basic functions. The basic software also contains so

10、me function blocks. The user program is the total of all the statements and declarations programmed by the user. The user program consists of a number of block types such as organization blocks (OBs), program blocks (PBs), function blocks (FBs), sequence blocks (SBs) and data blocks (DBs). They are

11、available for structuring the user program and each of the blocks is used for different tasks. Many control applications exist that require the switching (on or off) of various outputs as a function of the condition (on or off) of a number of input devices. This type of control is referred to as swi

12、tching control of logic control. The relative simplicity of switching control makes it attractive for use in automatic machines and processes where the requirement is for the machine or process to follow a set sequence of operations. One example is a transfer linewherein each station performs a cert

13、ain operation on a part, after which the processed part is transferred to the next station and replaced by an unprocessed part from the precious station. Another example is a process in which various dry bulk materials are weighed, combined mixed and ultimately discharged. Sequential control can be

14、implemented in a number of ways, including electro-mechanical relays and various pneumatic, fluidic and solid-state devices. This chapter, however, focuses on digital computer systems that are primarily dedicated to the implementation of switching control. These special-purpose computers are called

15、programmable logic control. In light of the preceding discussion, it is clear that the role of the control unit is to continuously scan its program, setting outputs on or off depending on the switch conditions of the inputs. The controller must therefore be provided with a program that defines the d

16、esired switching sequences. Notes 1、With each module having sixteen “points” of either input or output, this PLC has the ability to monitor and control dozens of devices. 由With所引导的短语形成逻辑主谓结构，作状语。本句可译为：PLC中的每个模块都有16个“点”的输入或输出，具有监视和控制数十台装置的能力。2、The relative simplicity of switching control makes it att

17、ractive for use in automatic machines and processes where the requirement is for the machine or process to follow a set sequence of operations.本句为定语从句。在主句在，it是形式宾语，代替for useprocesses。本句可译为：相对简单的转换控制使其很容易地用于自动机床和过程中。在那里，要求机床和过程跟随一套顺序操作。1、PLCs have some functions such as timing, drum sequencing and so

18、 on.2、One advantage of PLCs work as remote monitoring and control through digital computer networks. 3、PLCs are lack of some functions of accepting information from various input switching devices.4、The PLC software consists of the operating system, the basic software and the user program according

19、to the passage.5、These special-purpose computers are not regarded as programmable logic control.EXERCISE 1 Mark the following statements with T (True) or F (False) according to the passage. (T)(T)(F)(T)(F)time-delay relay _ 开关装置3. function block _ _ 程序模块5. limit switch _ 数据模块7. ladder diagram _ 用户程序

20、 EXERCISE 2Translate the following phrases into Chinese or English. 时滞继电器switching device功能模块program blocks限位开关data block梯图user programPassage B Sheet Metal Forming Signal connection and programming standards vary somewhat between different models of PLC, but they are similar enough to allow a gener

21、ic introduction to PLC programming here. The following illustration (Figure 10-5) shows a simple PLC, as it might appear from a front view. Two screw terminals provide connection to 120 volts AC for powering the PLCs internal circuitry, labeled L1 and L2. Six screw terminals on the left-hand side pr

22、ovide connection to input devices, each terminal representing a different input channel with its own X label. The lower-left screw terminal is a Common connection, which is generally connected to L2 (neutral) of the 120 VAC power source. Inside the PLC housing, connected between each input terminal

23、and the Common terminal, is an opto-isolator device (Light-Emitting Diode) that provides an electrically isolated high logic signal to the computers circuitry (a photo-transistor interprets the LEDs light) when there is 120 VAC power applied between the respective input terminal and the Common termi

24、nal. An indicating LED on the front panel of the PLC gives visual indication of an energized input (Figure 10-6): Output signals are generated by the PLCs computer circuitry activating a switching device (transistor, TRIAC, or even an electromechanical relay), connecting the Source terminal to any o

25、f the Y labeled output terminals. The Source terminal, correspondingly, is usually connected to the L1 side of the 120 VAC power source. As with each input, an indicating LED on the front panel of the PLC gives visual indication of an energized output (Figure 10-7). In this way, the PLC is able to i

26、nterface with real-world devices such as switches and solenoids. The actual logic of the control system is established inside the PLC by means of a computer program. This program dictates which output gets energized under which input conditions. Although the program itself appears to be a ladder log

27、ic diagram, with switch and relay symbols, there are no actual switch contacts or relay coils operating inside the PLC to create the logical relationships between input and output. These are imaginary contacts and coils, if you will. The program is entered and viewed via a personal computer connecte

28、d to the PLCs programming port. Consider the following circuit and PLC program (Figure 10-8): If the pushbutton switch is pressed, however, power will be sent to the PLCs X1 input. Any and all X1 contacts appearing in the program will assume the actuated (non-normal) state, as though they were relay

29、 contacts actuated by the energizing of a relay coil named X1. In this case, energizing the X1 input will cause the normally-open X1 contact will close, sending power to the Y1 coil. When the Y1 coil of the program energizes, the real Y1 output will become energized, lighting up the lamp connected t

30、o it (Figure 10-9): When the pushbutton switch is unactuated (unpressed), no power is sent to the X1 input of the PLC. Following the program, which shows a normally-open X1 contact in series with a Y1 coil, no power will be sent to the Y1 coil. Thus, the PLCs Y1 output remains de-energized, and the

31、indicator lamp connected to it remains dark . It must be understood that the X1 contact, Y1 coil, connecting wires, and power appearing in the personal computers display are all virtual. They do not exist as real electrical components. They exist as commands in a computer program - a piece of softwa

32、re only - that just happens to resemble a real relay schematic diagram. Furthermore, since each output in the PLC is nothing more than a bit in its memory as well, we can assign contacts in a PLC program actuated by an output (Y) status. Take for instance this next system, a motor start-stop control

33、 circuit (Figure 10-10): The pushbutton switch connected to input X1 serves as the Start switch, while the switch connected to input X2 serves as the Stop. Another contact in the program, named Y1, uses the output coil status as a seal-in contact, directly, so that the motor contactor will continue

34、to be energized after the Start pushbutton switch is released. You can see the normally-closed contact X2 appear in a colored block, showing that it is in a closed (electrically conducting) state. If we were to press the Start button, input X1 would energize, thus closing the X1 contact in the progr

35、am, sending power to the Y1 coil, energizing the Y1 output and applying 120 volt AC power to the real motor contactor coil. The parallel Y1 contact will also close, thus latching the circuit in an energized state (Figure 10-11). Now, if we release the Start pushbutton, the normally-open X1 contact w

36、ill return to its open state, but the motor will continue to run because the Y1 seal-in contact continues to provide continuity to power coil Y1, thus keeping the Y1 output energized. To stop the motor, we must momentarily press the Stop pushbutton, which will energize the X2 input and open the norm

37、ally-closed contact, breaking continuity to the Y1 coil. When the Stop pushbutton is released, input X2 will de-energize, returning contact X2 to its normal, closed state. The motor, however, will not start again until the Start pushbutton is actuated, because the seal-in of Y1 has been lost. EXERCI

38、SE 3 Choose the best operation orders according to the information given. A. Wire to Board B. Circular Connectors C. Board to BoardD. Terminal Blocks E. PCB ConnectorsCEABDsv Safety Valve _2. TB Tee-bend _3. T.O. Technical Order _4. tpi Teeth Per Inch _5. TR Technical Regulation _6. TS Tool Steel _

39、7.VHF Vary High Frequency _8. WB Wheel Base _ EXERCISE 4Abbreviations are very useful in practical work. Read them and then translate them into corresponding Chinese terms. 安全阀T型弯头技术条令每齿轮技术规程工具钢特高频率轴距Part II Glance at Conventional Machine Tool Structures The following is the Vice Jaw Structures。 No.

40、NameExplanation1PC for PLC programming用于PLC编程的个人计算机2Screw terminals for input lines输入螺丝接线端子排3Screw terminals for output lines输出螺丝接线端子排4Power Supply电源5Communication通讯6Expansion Connection拓展连接7Input Processing Circuit输入处理电路8Output Processing Circuit输出处理电路9Memory存储器10CPU中央处理器EXERCISE 5The following is

41、the Vice Jaw. After reading them, you are required to choose the suitable words or phrases given below. Circuit Breakers PLC Digital Output Cards Digital Input CardsAnalog Input Cards Relay Switches Power Supply Nema 12 EnclosureOperator Interface Terminal Transient Surge Protectors Power Supply PLC

42、 Digital Input Cards Digital Output Cards Analog Input Cards Transient Surge Protectors Circuit Breakers Relay Switches Operator Interface Terminal Nema 12 Enclosure Part III Simulated WritingSection A Match Your SkillThe following is the Lathe Accessories, and you can understand the name of Inner D

43、ial Caliper Gauge. Explanations of the Programmable Logic Controller Terms No.NameExplanation1Analog output module模拟输出模块2Analog input module模拟输入模块3Memory board 存储器板4CPU moduleCPU模块5Power supply module电源模块6Base unit底板7I/O controller输入/输出控制器8I/O controller connecting cable输入/输出控制器连接电缆9Cables for conne

44、cting peripheral devices连接外设的电缆10Communication module通讯模块11Counter module, positioning module计数、定位模块12Input module输入模块13Output module输出模块14Dummy module空模块EXERCISE 6Complete the information by translating the part given in Chinese. Toshiba S2E/ST2 Small PLCsToshibas S2E/S2T PLC controllers are small,

45、 modular type programmable controllers suitable for simple Relay replacement all the way to complex control applications. Toshiba S2E/S2T is 3rd generation T2 Series CPUs used with V-Series racks, I/O, and Power Supplies. The S2E/S2T provides a functional, economical, and compact solution to a wide

46、range of applications in automotive, machine control, and process control systems.Key Features T-Series Compatible. Any program written for a T-Series CPU can be downloaded directly into the S2E/S2T without modification. Comment Storage in CPU. Device/register tags and comments can be stored in CPU

47、module. Tags and comments can be viewed in the on-line mode without access to the original program. Large Program Memory. Section B Have a TryThis section will help you to understand several forms of machining, and you can see the simple way a small part is produced. External Operations Radial depth

48、 of cut - The depth of the tool along the radius of the work-piece as it makes a cut, as in a turning or boring operation. A large radial depth of cut will require a low feed rate, or else it will result in a high load on the tool and reduce the tool life. Therefore, a feature is often machined in s

49、everal steps as the tool moves over at the radial depth of cut. EXERCISE 7This section is to test your ability to Identifying following features of different operations. End milling (Slot) End milling (Pocket) End milling (Profile)End milling (Profile) End milling (Slot) End milling (Pocket) Part IV

50、 Broaden Your Horizon - Practical Activity PLC Process Control System A Programmable Logic Controller (PLC) is an industrial computer control system that continuously monitors the state of input devices and makes decisions based upon a custom program, to control the state of devices connected as outputs. Almost any production line, machine function or process can be automated using a PLC. The sp