| This thesis is related to the redundant control system based on use of PLC. Most of control applications are both based on traditional logic programmable controllers. It has seen that faults create errors, which, in turn, lead to system failures. The development of a Redundant control system calls for the combined utilization of a set of four techniques:fault prevention:how to prevent the occurrence or introduction of faults; fault tolerance:how to deliver correct service in the presence of faults; fault removal:how to reduce the number or severity of faults fault forecasting:how to estimate the present number, the future incidence, and the likely consequences of faults.This paper carries out two methods:(1) Two PLCs operating simultaneously, if these two PLCs are not in agreement with each other, for example, there are some differences between their input signal, then the system shutdown. (2) Two PLCs are used in this system, but just one PLCs runs at one time. If the system finds there is something wrong with the functional elements, the second PLC will be started.Achieving dependable control systems call for the combined utilization of fault avoidance methods or fault tolerance methods, providing satisfactory service in the presence of faults via protective. Dependability is the term used to precisely describe those system properties that allow us to rely on a system functioning as required. Dependability includes, among other attributes, reliability, safety, security, and availability. From the dependability point of view, we will be concerned in particular with the reliability of the database replication solutions. When systems are built using "off-the-shelf products, fault tolerance (Redundancy) is often the only viable way for obtaining required system dependability. Fault-tolerant systems are able to continue operation properly in the event of failures, after some faults have manifested themselves. Hence the concept of fault tolerance assumes that faults are present in the system, and that it is possible for the system to handle them without external interventions. The goal of fault tolerance is to ensure that system faults do not result in system failure. For this reason, this paper describes two methods of fault tolerances (two PLCs run simultaneously, if both PLCs are not in agreement with each other, then the difference detected trigger the fallback position on a safe position and second method, based on two PLCs but only one operates, the changeover will take place upon detection of a failure of the functioning part)In view of the above situation, the main working contents include the following items:1. The control fundamental, that gives an approach of control system, consists of monitoring the state of a critical parameter, detecting when it varies from the desired state, and taking measurement to modify it.2. The concept of redundant control system based on PLCs, which is reflected by duplication of elements in electronic equipment to provide alternative channels in the case of failures to guarantee dependability.3. To understand conception of the redundant control system better, some architectures of the redundant control system were designed, and then a limited dual redundant control system by use of PLCs4. Experiments, deductions of formulations and designs of system hardware and software are made in this paper. In system hardware, the "work by" configuration, both devices controls (PLCs) are used to accomplish and feeding with the same synchronized inputs and change their states in terms of the modes of inputs only in the same manner. If the discrepancy between these devices (PLCs) is detected, the system will shutdown automatically. Secondly, the "standby" configuration, just one device control, is used, which is sufficient to perform the function if the system runs smoothly. In the case of system failures, the network communication is maintained by starting the redundant control system. In system software design, ladder logic programming is applied to provide traditional ladder logic network techniques for high performance distribute and interlocks control. The ladder logic elements connect the output port of power and the output port of soft element coils.In fact, the control system (workby) has two programmable logic controllers (PLC1-A, PLC2-B) fitted with redundancy couplers connected together by a link, such as Ethernet, and with analog couplers each receiving one of the two input channels (A,B) derived from a common signal supplied from a detector. The input signals from the couplers are sampled, and the sample values and frequency of sampling is stored in memory. Second, the "standby" configuration, here just one device control is sufficient to perform the function, the network communication is maintain in case of failure of functioning system by switch over the second system. In a redundant system, either system CPU module runs the programs, controls the system and communicates with the network. The system that includes the CPU running the programs is referred to as the control system, the other system serves as backup is referred to as the standby system.To summarize, the redundant methods considered were simulated using a facility in laboratory (Mitsubishi FA experimental platform). The field of this application is that the high availability and reliability, thus justifying the duplication of control system in order to fight any random errors that may occur in any one of the control system device components. The system of control is designed and expected, in order to obtain industrial goals. |
