关于零件电镀生产线PLC控制系统设计外文翻译.doc

PLC QUESTION

PLC which should pay attention in the application is specially the control device which serves for the industrial production, usually does not need to take any measure, may use directly in the industry environment. But, when the production environment is too bad, the electromagnetic interference is special intense, or installs uses improper, cannot guarantee PLC the normal operation, therefore should pay attention to the following question in the use.
First, installment and wiring
(1) The power line, the pilot wire as well as the PLC power line and the I/O line should distinguish the wiring, between the insulating transformer and PLC and I/O should use the double rubberized wire connection.
(2) PLC should be far away from the strong jamming source like electric welding machine, the high efficiency silicon rectifier unit and the large-scale power equipment, cannot install with the high-pressured electric appliance in the identical switch cabinet.
(3) The input and output of PLC are best separate the line, the switch quantity and the simulation quantity must separate the placing. The simulation quantity signal's transmission should use the shielded wire, the shielding layer should an end or the both sides earth, and the earth resistance should be smaller than the shielding layer resistance 1/10.
(4) The PLC elemental area and the expansion unit as well as functional module's ties cable should lie alone, prevents the outside signal the disturbance.
(5) The exchange output line and the direct-current output line do not use the identical root electric cable, the output line to be far away from the high tension line and the power line as far as possible, avoids parallel.
Second, I/O end wiring
1. Input wiring (1) inputs the wiring not to surpass 30 meters generally. But if the environment disturbance is small, when the loss of voltage is not big, the input wiring may suitable long.
(2)Inputs/the output line not to be able to use the identical root electric cable, the input/output line to be separated.
(3)Uses the normally opened contact form to connect the input end as far as possible, causes the establishment the trapezoidal chart to be consistent with the relay schematic diagram, is advantageous for reading.
2. Outgoing junction
(1) The out-put wiring divides into the independent output and the public output. In not group, may use the different type and the voltage class output voltage. But can only use the identical type, the identical voltage class power source in the identical group's output.
(2) Because the PLC output element is sealed on the print circuit wafer, and connects to the terminal strip, if will connect output element's load short circuit, will burn down the print circuit wafer, therefore, application fuse protection output element.
(3)Uses when the relay outputs, withstands inductive load's size, will affect relay's service life, therefore, time use inductive load the selective relay working life must be long.
(4) The PLC output load possibly has the disturbance, must therefore take the measure to control, if direct-current output's after flow guarantees protects, the exchange output anti- accommodates the absorbing circuit, the transistor and the bidirectional thruster output by-passed resistor protection.
Third, outside security electric circuit to guarantee that the overall system can under the secure state the reliable work, avoids, because the external power supply breaks down, PLC to present the heavy economic loss which and the person casualty exceptionally, the disoperation as well as outputs by mistake creates, PLC the outside should install the essential protection circuit.
(1) Stops the electric circuit anxiously. Regarding can cause the user to cause the damage the dangerous load, besides performs in the control procedure to consider, but also exterior should design the emergency stop electric circuit, causes when PLC breaks down, can cause the injury load power source reliably to shut off.
(2)Fragment. The forward and reverse revolution and so on reversible operation's control system must establish the exterior electric appliance interlock protection; the reciprocation moves and rises and falls motion the control system, must establish the exterior spacing protection circuit.
(3)The programmable controller has self-checking functions and so on surveillance timer, when inspects exceptionally, outputs completely the closure. But when programmable controller CPU breakdown cannot control the output, therefore, regarding can cause the user to cause the damage the dangerous load, to guarantee that the equipment moves under the secure state, must design the external circuit to protect.
(4) Power source load protection. If the PLC power source breaks down, the interruption interval is short in 10 seconds, PLC works not affected, if the power source interrupt surpasses 10 second or the power source drops surpasses the permissible value, then the PLC stop work, all output also separates; when the power source restores, if RUN input connection, then operates carries on automatically. Therefore, to establish the essential current limiting protection circuit to some easy over-loading's input device.
(5) Significant breakdown warning and protection. Regarding easy to have heavy accident's place, to guarantee the control system when the heavy accident occurs still the reliable warning and the protection, should have with the significant breakdown the contacting signal to output through the external circuit, caused the control system to move under the safe condition.
Fourth, PLC earth the good earth is guaranteed that the PLC reliable work the important condition, may avoid the heterogametic the voltage surge harm. PLC meets the grounding and machine's ground terminal docking, meets the grounding the cross-sectional area should not to be smaller than 2mm2, the earth resistance is smaller than 100Ω; If must use the expansion unit, its ground point should accept after checking with the elemental area earth in the same place. In order to suppress adds in the power source and the input end, out-port's disturbance, should joins the special-purpose grounding to PLC, the ground point should with the power equipment (for example electrical machinery) the ground point separate; If cannot meet this kind of requirements, must achieve with the other equipment public earth, forbids to establish contacts the earth with other equipment. The ground point should approach PLC as far as possible.
Fifth the redundant system and hot backup system in profession in and so on petroleum, chemical industry, metallurgy certain systems, the request control device has the extremely high reliability. If the control system breaks down, will create the production suspension, the raw material massive wastes or the equipment trouble, will create the enormous economic loss to the enterprise. But depends on the enhancement control system hardware's reliability to satisfy the above request is only not enough, because the PLC itself reliable enhancement has certain limit. Uses the redundant system or the hot backup system can solve the above problem quite effectively.
(1) Redundancy control system in redundancy control system, entire PLC control system (or in system most important part, if the CPU module) of two set of identical system composition. Two CPU module use same user program multi-tasking one is advocates CPU, another is spare CPU; advocates the CPU work, but the spare CPU output is forbidden, when advocates CPU breaks down, spare CPU automatic investment movement. This cut process is controlled by the redundancy processing unit RPU, the switching time in 1~3 scanning periods, the I/O system's cut is also completes by RPU.
(2) Hot backup system in the hot backup system, two CPU with the communication connection connects in together, which is at circular telegram condition .When the system presents the breakdown, advocates CPU informs spare CPU to make the spare CPU work. This cut process is not too generally quick, but its structure is simpler than the redundant system.
译文：PLC 在应用中应注意的问题

PLC是专门为工业生产服务的控制装置，通常不需要采取什么措施，就可以直接在工业环境中使用。但是，当生产环境过于恶劣，电磁干扰特别强烈，或安装使用不当，都不能保证PLC的正常运行，因此在使用中应注意以下问题
一、安装与布线
　　1、 动力线、控制线以及PLC的电源线与I/O线应分别配线，隔离变压器与PLC与I/O之间应采用双胶线连接。
　　2、 PLC应远离强干扰源如电焊机、大功率硅整流装置与大型动力设备，不能与高压电器安装在同一个开关柜内。
　　3、 PLC的输入与输出最好分开走线，开关量与模拟量也要分开敷设。模拟量信号的传送应采用屏蔽线，屏蔽层应一端或两端接地，接地电阻应小于屏蔽层电阻的1/10。
　　4、 PLC基本单元与扩展单元以及功能模块的连接线缆应单独敷设，以防止外界信号的干扰。
　　5、 交流输出线与直流输出线不要用同一根电缆，输出线应尽量远离高压线与动力线，避免并行。
二、I/O端的接线
　　1、 输入接线
　　（1）输入接线一般不要超过30米。但如果环境干扰较小，电压降不大时，输入接线可适当长些。（2）输入/输出线不能用同一根电缆，输入/输出线要分开。（3）尽可能采用常开触点形式连接到输入端，使编制的梯形图与继电器原理图一致，便于阅读。
　2． 输出连接
　　（1）输出端接线分为独立输出与公共输出。在不同组中，可采用不同类型与电压等级的输出电压。但在同一组中的输出只能用同一类型、同一电压等级的电源。（2）由于PLC的输出元件被封装在印制电路板上，并且连接至端子板，若将连接输出元件的负载短路，将烧毁印制电路板，因此，应用熔丝保护输出元件。（3）采用继电器输出时，所承受的电感性负载的大小，会影响到继电器的使用寿命，因此，使用电感性负载时选择继电器工作寿命要长。（4）PLC的输出负载可能产生干扰，因此要采取措施加以控制，如直流输出的续流管保护，交流输出的阻容吸收电路，晶体管及双向晶闸管输出的旁路电阻保护。
三、外部安全电路
　　为了确保整个系统能在安全状态下可靠工作，避免由于外部电源发生故障、PLC出现异常、误操作以及误输出造成的重大经济损失与人身伤亡事故，PLC外部应安装必要的保护电路。
　　（1）急停电路。对于能使用户造成伤害的危险负载，除了在控制程序中加以考虑之外，还应设计外部紧急停车电路，使得PLC发生故障时，能将引起伤害的负载电源可靠切断。（2）保护电路。正反向运转等可逆操作的控制系统，要设置外部电器互锁保护；往复运行及升降移动的控制系统，要设置外部限位保护电路。（3）可编程控制器有监视定时器等自检功能，检查出异常时，输出全部关闭。但当可编程控制器CPU故障时就不能控制输出，因此，对于能使用户造成伤害的危险负载，为确保设备在安全状态下运行，需设计外电路加以防护。（4）电源过负荷的防护。如果PLC电源发生故障，中断时间少于10秒，PLC工作不受影响，若电源中断超过10秒或电源下降超过允许值，则PLC停止工作，所有的输出点均同时断开；当电源恢复时，若RUN输入接通，则操作自动进行。因此，对一些易过负载的输入设备应设置必要的限流保护电路。（5）重大故障的报警及防护。对于易发生重大事故的场所，为了确保控制系统在重大事故发生时仍可靠的报警及防护，应将与重大故障有联系的信号通过外电路输出，以使控制系统在安全状况下运行。
四、PLC的接地
　　良好的接地是保证PLC可靠工作的重要条件，可以避免偶然发生的电压冲击危害。PLC的接地线与机器的接地端相接，接地线的截面积应不小于2mm2 ，接地电阻小于100Ω；如果要用扩展单元，其接地点应与基本单元的接地点接在一起。为了抑制加在电源及输入端、输出端的干扰，应给PLC接上专用地线，接地点应与动力设备（如电机）的接地点分开；若达不到这种要求，也必须做到与其它设备公共接地，禁止与其它设备串连接地。接地点应尽可能靠近PLC。
五、冗余系统与热备用系统
　　在石油、化工、冶金等行业的某些系统中，要求控制装置有极高的可靠性。如果控制系统发生故障，将会造成停产、原料大量浪费或设备损坏，给企业造成极大的经济损失。但是仅靠提高控制系统硬件的可靠性来满足上述要求是远远不够的，因为PLC本身可靠性的提高是有一定的限度。使用冗余系统或热备用系统就能够比较有效地解决上述问题。
　　1． 冗余控制系统
　　在冗余控制系统中，整个PLC控制系统（或系统中最重要的部分，如CPU模块）由两套完全相同的系统组成如图2所示。两块CPU模块使用相同的用户程序并行工作，其中一块是主CPU，另一块是备用CPU；主CPU工作，而备用CPU的输出是被禁止的，当主CPU发生故障时，备用CPU自动投入运行。这一切换过程是由冗余处理单元RPU控制的，切换时间在1-3个扫描周期，I/O系统的切换也是由RPU完成的。
　　2． 热备用系统
　　在热备用系统中，两台CPU用通讯接口连接在一起，均处于通电状态如图3所示。当系统出现故障时，由主CPU通知备用CPU，使备用CPU投入运行。这一切换过程一般不太快，但它的结构有比冗余系统简单