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PLC与西门子s7-200
PLC的发展与简介
美国数字设备研制出世界上第一台可编程控制器PLC并在通用汽车生产线上使用，并取得的满意的效果，可编程控制器从此诞生。PLC是一种新型的具有极高可靠性的通用自动化控制装置。它以微处理器为核心，有机地将微型计算机技术、自动化控制技术及通信技术融为一体。其应用非常广泛，有钢铁、石油。化工、电力、汽车、纺织、交通运输、环保及文化娱乐方面。其大部分应用可以归为下面几类。
顺序控制：这是PLC最基本、最广泛的应用领域，它取代了传统的继电器的使用，用于单机控制、多机控制、自动化生产线的控制。列如，数控机床等；位置控制：大多数PLC制造商已经将其广泛的运用于各种机械，如金属切削机床、装配机床等；模拟量控制：PLC通过模拟量的输入与输出模块，实现了数字量与模拟量的交换，并对模拟量进行控制，列如压力与温度的控制；数据处理：现代的PLC具有数学运算、数据传输、转换、排序和查表等功能，也能完成数据的采集分析和处理。通信联网：PLC的通信包括PLC与PLC之间、PLC与上位计算机、PLC与其他智能设备之间的通信，PLC与通用计算机可以直接或通过通讯处理单元、通讯转换器相连接构成网络，所实现信息的交换，并可构成“集中管理、分散控制”的分布式控制系统，满足工厂自动化系统的需要。
PLC系统的特点：
可靠性高，PLC作为一种通用的工业控制器，它必须能够在各种不同的工作环境中正常工作。对工作的环境要求较低，抗外部干扰能力强，平均无故障时间长；使用方便灵活，PLC采用了基本单元扩展或者是模块化的结构形式，因此，输入/输出信号的数量，形式，驱动能力等都可以根据实际控制要求进行选择与确定，而且在需要时可以随时更换，近年来，PLC的特殊模块增多这些可以满足不同的控制要求，使PLC的使用更加灵活与多变；编程简单，PLC的优越性主要体现在它采用了独特的，多种面向广大工程设计人员的编程语言，如指令表，梯形图，逻辑功能图，顺序功能图等；程序简洁，明了适合各类技术人员的传统习惯，即使是没有计算机知识的人员也很统一掌握，特别是梯形图与逻辑功能图，形象直观，动态监测效果逼真，且与计算机控制容易。
plc控制电路与继电器控制电路相比的话有下面的优点：从控制方式上面看：在电器控制硬接线上，如果你已经开始接线了，并且已经接好，这样的话改的话是非常不容易的；而对于plc的软接线，只需改变控制程序就可以改掉。这样就节约了很多的人力物力，节约了很多资金。从工作方式上面看：电器控制的工作是并行的，这样的话会受到制约。而plc是串行工作，不受会受到制约。从控制速度上面看：电器控制速度慢，触点易抖动，而plc是用半导体来控制的，速度非常的快，没有触点，所以就不会抖动。这样的话也就没有硬件损耗的。从定时、记数上面看：电器控制定时精度不是太高，容易受到外界的影响，这样的话会影响生产结果的，比如说是外界的温度，湿度等等。并且电器控制没有记数功能；plc的时钟脉冲是由晶振产生的，所以精度很高，定时的范围也很宽；并且它还有有记数功能。从稳定可靠、维护上面看：电器控制的触点多，会产生机械的磨损和电弧的烧伤，同时电器控制的接线也多，稳定可靠、维护性能也差；plc没有触点，同时可以运用的时间还比较长，并且有自身诊断功能，这样的话就又可以节省人力物力了。
单片机系统的特点：
单片机对环境有一定的要求，它对环境的适应能力比较低，同时可靠性也不是很高。相对于编程上的话与PLC相比就更加的难以学习了，单片机采用C语言或者是汇编语言，这些高级语言都是不容易学习和灵活运用的。这个和PLC语言相比，难以学习，不容易上手。同时在功能上的话，其功能单一只具有使用中所需要的功能，就没有什么别的功能了。有一点不能不得承认，它还是有优点的，它的结构简单，处理速度快，本身小巧、功耗低，这样的话，在有些地方还是需要这样的控制部件的。单片机不具有自开发能力而且编写进水、洗涤、脱水等程序的话会相对复杂。同时在设计控制系统硬件的时候，电路中还要有多种电路保护装置，如果这样的话，就会硬件部分更加的复杂，隐含的故障率会有所提高，而且也不可以重复的使用。无形中也增加了维修的费用。
S7-200 的特征
S7-200 是一种小型的可编程序控制器，适用于各行各业，各种场合中的检测、监测及控制的自动化。S7-200系列的强大功能使其无论在独立运行中，或相连成网络皆能实现复杂控制功能。因此S7-200系列具有极高的性能/价格比。
S7-200系列出色表现在以下几个方面：
极高的可靠性;极丰富的指令集;易于掌握;便捷的操作;丰富的内置集成功能; 实时特性; 强劲的通讯能力; 丰富的扩展模块.
S7-200系列在集散自动化系统中充分发挥其强大功能。使用范围可覆盖从替代继电器的简单控制到更复杂的自动化控制。应用领域极为广泛，覆盖所有与自动检测，自动化控制有关的工业及民用领域，包括各种机床、机械、电力设施、民用设施、环境保护设备等等。如：冲压机床，磨床，印刷机械，橡胶化工机械，中央空调，电梯控制，运动系统。S7-200系列PLC可提供4个不同的基本型号的8种CPU供您使用。
CPU单元设计
集成的24V负载电源：可直接连接到传感器和变送器（执行器），CPU 221，222具有180mA输出， CPU 224，CPU 224XP，CPU 226分别输出280，400mA。可用作负载电源。不同的设备类型。CPU 221~226各有2种类型CPU，具有不同的电源电压和控制电压。本机数字量输入/输出点。
CPU 221具有6个输入点和4个输出点，CPU 222具有8个输入点和6个输出点，CPU 224具有14个输入点和10个输出点，CPU 224XP具有14个输入点和10个输出点，CPU 226具有24个输入点和16个输出点。本机模拟量输入/输出点。CPU 224XP具有2个输入点，1个输出点。中断输入。允许以极快的速度对过程信号的上升沿作出响应。高速计数器。CPU 221/222，4个高速计数器（30KHz），可编程并具有复位输入，2个独立的输入端可同时作加、减计数，可连接两个相位差为90°的A/B相增量编码器。CPU224/224XP/226。6个高速计数器（30KHz），具有CPU221/222相同的功能。CPU 222/224/224XP/226。可方便地用数字量和模拟量扩展模块进行扩展。可使用仿真器（选件）对本机输入信号进行仿真，用于调试用户程序。
PLC系统的特点：
可靠性高，PLC作为一种通用的工业控制器，它必须能够在各种不同的工作环境中正常工作。对工作的环境要求较低，抗外部干扰能力强，平均无故障时间长。使用方便灵活，PLC采用了基本单元扩展或者是模块化的结构形式，因此，输入/输出信号的数量，形式，驱动能力等都可以根据实际控制要求进行选择与确定，而且在需要时可以随时更换，近年来，PLC的特殊模块增多这些可以满足不同的控制要求，使PLC的使用更加灵活与多变。编程简单，PLC的优越性主要体现在它采用了独特的，多种面向广大工程设计人员的编程语言，如指令表，梯形图，逻辑功能图，顺序功能图等，程序简洁，明了适合各类技术人员的传统习惯，即使是没有计算机知识的人员也很统一掌握，特别是梯形图与逻辑功能图，形象直观，动态监测效果逼真，且与计算机控制容易。
单片机系统的特点：
要求环境，单片机对环境的适应能力较低，可靠性差。编程和PLC相比难以学习，主要是单片机采用汇编语言或者是C语言，这些高级语言和PLC语言相比，难以学习。功能单一只具有使用中所需要的功能。但是，它结构简单，处理速度快。
采用PLC控制系统将大大提高工作效率，和适应工作环境的能力。由单片机为中心控制系统工作的。首先由于单片机的指令系统相对复杂，编写洗涤、脱水程序相对复杂；其次，在设计控制系统硬件时．要有多种电路保护装置，如电流保护、电压保护、过载保护、过热保护及欠压保护等等 这样增加了硬件的复杂性，隐含较高的故障率无形地增加了维修成本费用，在各种控制系统中广泛运用的PLC能克服单片机的缺点。它是整体模块，集中了驱动电路、检测电路和保护电路以及通讯联网功能。因此在运用中，硬件也相对简单，提高控制系统的可靠性。另外它的编程语言也相对简单。
PLC and Siemens S7-200
The development and introduction of PLC
America digital equipment developed the world's first programmable controller PLC and used in GM production line, and obtained satisfactory results, the programmable controller is born. PLC is a kind of general automation is a highly reliable new control device. It takes microprocessor as its core, integrating computer technology, automatic control technology and communication technology com. Its application is very extensive, iron and steel, petroleum. Chemical, electric power, automotive, textile, transportation, environmental protection and cultural entertainment. Most of its application can be classified intothe following categories.
Sequence control: This is PLC the most basic, a wide range of applications, it replaces the traditional relay control, for single control, machine control, automatic production line. For example, the CNC machine tool; position control :most PLC manufacturers have be widely used in all kinds of machinery, such asmetal cutting machines, assembly machines; analog control: PLC through theinput and output module of the exchange of analog, digital and analog, andcontrol of analog, column such as the control of temperature and pressure; data processing: Modern PLC with mathematics, data transmission, conversion,sorting and lookup table function, also can complete the data acquisition and analysis and processing of data. Communication: communication including PLC,PLC and PLC communication between PLC and host computer, PLC and other intelligent devices, PLC and general computer can directly or through a communication processing unit, communication converter connected to anetwork, exchange information, and can constitute a "distributed control system for centralized management, decentralized control", to meet the needs of factory automation system.
The characteristics of PLC system:
High reliability, PLC is a general industrial controller, it must be able to work in a variety of different work environments. The work environment requirements are relatively low, anti external interference, the mean time to failure is long; flexible and easy to use, PLC adopts the basic unit or structure, modular and therefore,the number of input / output signal form, driving ability, can according to the actual control requirements are selected and determined, and when in need can be replaced at any time, in recent years, the special module of PLC increasedwhich can meet different control requirements, the use of PLC more flexible and varied; the programming simple, the superiority of PLC is mainly reflected in theunique, many for the majority of engineers in the design of programming languages, such as a list of instructions, ladder diagram the function diagram,logic, sequential function chart; simple procedures, suitable for all kinds of technical personnel understand the tradition, even if there is no computerknowledge staff is also very unified control, especially the ladder diagram andlogic function diagram, vivid, lifelike and dynamic monitoring, computer control and easy to.
Advantages of PLC control. Compared with the relay control circuit has the following: from the control above: in the electrical control hard wiring, if you have already started wiring, and has received good, then change it is very not easy;and for soft connection PLC, only need to change control procedures you canget rid of. This will save a lot of manpower and resources, saving a lot of money.See above from work: electrical control work is parallel, it will be restricted by.PLC is the serial work, not subject to restriction. From the control speed above:electrical control speed is slow, easy contact jitter, and PLC is used to control the semiconductor, speed is very fast, no contact, so will not shake. So there is nohardware loss. From the timing, count above: electrical control timing accuracy is not too high, vulnerable to external influence, it will affect the production results,such as the outside temperature, humidity etc.. And electrical control withoutcounting function; PLC clock pulse is generated by oscillator, so the precision is very high, the timing of the scope is very wide; and it has counting function. From the stable and reliable, maintenance above: contact electrical control, will produce mechanical wear and arc burns, wiring and electrical control are morestable and reliable, maintenance, performance is poor; PLC did not contact, alsocan use time is relatively long, and has self diagnosis function, so again it may save manpower and material resources.
Characteristics of single chip computer system:
SCM has certain requirements on the environment, the ability to adapt to theenvironment is relatively low, and the reliability is not high. With respect to theprogramming it compared with PLC is more difficult to learn, the SCM C language or assembly language, the language is not easy and flexible use of the learning.Compared to this, and PLC language is hard to learn, not easy to use. At the same time on the function words, the single function only has the requiredfunctions in use, no what other functions. One can't not admit, it has its merits, ithas the advantages of simple structure, fast processing speed, itself compact,low power consumption, so, in some places still need to control the parts such asthe. Does not have self development ability and preparation of water, washing,dehydration process would be relatively complex. At the same time in the designof control system hardware, circuit also has a variety of circuit protection device,if so, will the hardware part is more complex, hidden fault rate will be increased,but also can not duplicate. It also increases the cost of repair.
The characteristics of S7-200
S7-200 is a small programmable controller, applicable to all walks of life,automatic detection, monitoring and control of various occasions. The powerfulfunction of S7-200 series to enable it to operate independently, or connected into a network can realize the complex control function. Therefore, the S7-200 series with high performance / price ratio.
S7-200 series of outstanding performance in the following areas:
High reliability; the extremely rich set of instructions; easy to grasp; convenient operation; integrated feature rich; real-time performance; strong communicationability; expansion module is rich
S7-200 series plays its powerful functions in the distributed automation system.Use scope covers from a simple alternative relay control to more complex automatic control. Application areas are very broad, covering all with automatic detection, automatic control of industrial and civil fields, including machine tools,machinery, electric power facilities, civilian facilities, environmental protectionequipment and so on. Such as: punching machine, grinding machine, printing machinery, rubber machinery, central air conditioning, elevator control, motion system. S7-200 series PLC provides 4 basic types of different 8 CPU for you to use.
CPU unit design
Integrated 24V load power supply: can be directly connected to the sensor and transmitter (actuator), CPU 221222 with 180mA output, CPU 224, CPU 224XP,CPU 226 respectively output 280400mA. Can be used as the load power supply.Different device types. CPU 221~226 there are 2 types of CPU, with power supplyand control voltage of different. The digital input / output point.
CPU 221 has 6 input and 4 output points, CPU 222 has 8 input and 6 output points, CPU 224 has 14 input and 10 output points, CPU 224XP has 14 input and 10 output points, CPU 226 has 24 input and 16 output points. The analog input /output point. CPU 224XP has 2 input, 1 output points. Interrupt input. Allow rising at a rapid rate on the process of signal along the response. High speed counter.CPU 221/222, 4 high-speed counter (30KHz), programmable and has a reset input, 2 independent input at the same time as the addition, subtraction counting,can be connected with two phase difference of 90 ° A/B phase incremental encoder. CPU224/224XP/226. 6 high-speed counter (30KHz), has the same function as CPU221/222. CPU 222/224/224XP/226. Can be easily extendedmodule expansion with digital and analog. Can use the simulator (optional) for the simulation of the input signal, for debugging user program.
The characteristics of PLC system:
High reliability, PLC is a general industrial controller, it must be able to work in a variety of different work environments. The work environment requirements are relatively low, anti external interference, the mean time to failure length. Flexible and easy to use, PLC adopts the basic unit or structure, modular and therefore,the number of input / output signal form, driving ability, can according to the actual control requirements are selected and determined, and when in need can be replaced at any time, in recent years, PLC special module increased thesecan satisfy different the control requirements, the use of PLC more flexible and varied. The programming simple, the superiority of PLC is mainly reflected in theunique, many for the majority of engineers in the designof programming languages, suchasa listof instructions, ladder diagram, logic diagram,sequential function chart, the procedure is simple, and suitable for all kinds of technical personnel tradition, even the computer without the knowledge of thestaff is also very unified control, especially the ladder diagram and logic function diagram, vivid, lifelike and dynamic monitoring, computer control and easy to.
Characteristics of single chip computer system:
Requirements for environmental, SCM on the environment to adapt to lowcapacity, poorreliability. ProgrammingandPLC compared to learning, mainlyusing single-chip assemblylanguage or C language, compared to the advanced programming language and PLC language, it is difficult to learn. Single functiononly has the required functions in use. However, it has the advantages of simple structure, fast processing speed.
The use of PLC control system will greatly improve work efficiency, and the ability to adapt to the working environment. By the single-chip microcomputer as thecentral control system work. First, because the instruction system based on MCUis relatively complex, preparationof washing, dehydrationprocessrelativelycomplex; secondly, in the hardware design of the control system. A variety of circuit protection devices, such asthe currentprotection, voltageprotection,overloadprotection, overheatprotection, under voltage protection, so as to increase the complexity of the hardware, implied a higher rate of invisible faultincreased repair costs, widely used in various control system can overcome theshortcomings of PLC single chip microcomputer. It is the whole module, the drivecircuit, detectioncircuitand protectioncircuitand communication networking function. Therefore, when in use, the hardware is relatively simple, improve the reliability of the control system. In addition to its programming language is relatively simple.