Abstract: This paper introduces an automated system in the salt furnace, the use of Allen-Bradley ControlLogix PLC controller, dual CPU, to the realization of CPU redundancy control software. This is a most cost-effective effective means of improving system reliability. Keywords: CPU redundancy, ControlLogix, programming PLC is one of the three pillars of modern industry is the high reliability, application of a very wide range of industrial control products. In the medium and large modular PLC products, CPU module (CPU) is the central PLC. Some important industrial production lines often require continuous operation can not stop, and then the high reliability of PLC also can not guarantee Guzhang zero, thus, pairs of CPU s redundancy ???§??? is a production to meet continuing demands, increase system availability of Youxiaoshouduan. The following salt furnace automatic control system with detailed examples of the realization of two-CPU redundancy control method. I. Summary of molten salt furnace automated system Salt furnace automatic control system is a diaspore tube digestion important part of the production line to control the heating and circulating molten salt, with a molten salt heat to the cycle of heating aluminum ore slurry. Aluminum ore slurry heating crucial influence the final product - quality and production of alumina, therefore, the temperature of molten salt is very important to control and cycle control. As the salt furnace system in the pipeline of projects in the importance of taking into account Dao Salt is a kind of active chemicals, the temperature in different forms under different, under low temperature solidification, high temperature chemical reaction occurs under uncertainty, to corrosion wall even explosion, so safe, reliable operation simple and automated key management is the system design, so consider a two-CPU redundancy PLC, two IPC, high-quality sensors, transmitters and implementing agencies to control the two 12 million kilocalories of salt furnace, a salt pump, a valve of salt, a salt tank and other related equipment, and recycling of salt in the heating process automation, computer operation, monitoring and management automation. The system shown in Figure 1. controller PLC, IPC (including monitors), power and communications networks and systems such as the key test points to the important parts are redundant structure, two sets of industrial machines and large-screen display composed of two set of monitoring operations management units run in parallel; two redundant ControlNet high-speed communications network to transmit data simultaneously; two sets of DC power while the controller PLC, transmitter power supply and digital input module, the key test points and set the two sensors test data. Redundancy the reliability of key components of the system has doubled, make the control system s overall reliability has greatly improved. Second, dual CPU, PLC controller PLC controller is the system control center, all the conditions acquisition system signals, real-time control of equipment-related action; the same time monitoring the process parameters and equipment running, when dangerous conditions appears, timely audible and visual alarm, when the limit condition occurs, interlocking protection equipment to ensure production safety. To this end, we chose a product known for reliability of a new generation of Rockwell Automation control platform: AB ControlLogix series, taking into account the dual-CPU module redundancy to further improve system reliability, avoid failures caused by the emergence production stop or security incidents. 3, two pairs of comparison of CPU redundancy mode ControlLogix CPU redundancy to provide two solutions, a pure hardware redundancy, and the other for software redundancy. Hardware redundancy approach, the two CPU modules are inserted in two different racks, each rack in addition to CPU module, but also a communication module CNBR, hot standby module SRM, and between the two hot spare module connection cable, shown in Figure 2. software redundancy, the two CPU modules are inserted in the same framework, the use of backplane communication, redundancy control, shown in Figure 3. can be seen from the above, pure hardware redundancy to put in more hardware, the cost of a larger spending big. And software redundancy, only to increase a CPU module, costs very little, because the general as the CPU of this PLC in the heart of all manufacturers with spare parts, used spare parts to achieve redundancy control, not only improves the system reliability and maintenance (can be done inLine maintenance, does not affect the production line running), without a significant increase in costs. Just from the reliability analysis, pure software than hardware redundancy is not redundant edge. Because of the increased more components, modules, components and modules of these failures will also affect the reliability of the system. For example, when two hot spare module cable connection between the failure, the same redundancy control will fail. And software redundancy, an increase of only one CPU module, while the two CPU module failure rate is almost zero. One of the advantages of pure hardware redundancy is no need for specialized software programming, CPU state monitor and control heat transfer is prepared by the two modules to complete. And software redundancy state of the two CPU modules to monitor and control the transfer is solved by software programming. Therefore, the software redundant programming is relatively complex, large workload. comprehensive consideration of the above factors, the salt furnace automatic PLC system is the realization of software redundancy control of dual-CPU. 2 CPU module to run simultaneously in the system, a run in master mode, the other run in hot backup mode. When either a CPU failure to separate a CPU monitor and immediately alarm automatically to the normal CPU into master mode. CPU disturbance-free switching, the system has been controlled to ensure security, and to make the pipe production line has been in normal operation conditions of the good. 4, Software
CPU redundancy control of software programming mainly from the following two aspects: 1, control and transfer decisions block CPU running at the same time line, one in the main control mode, the other is in hot standby mode. Have primary control over the CPU with the output control, while the hot spare CPU also collect data and maintain communication links, but the output is disabled. Two CPU modules monitor each other s operational status and communication conditions are discovered each other s fault, immediately sent alarm through the ControlNet network, sent to IPC with, in the operation and management platform alarm. If the host CPU module failure, hot spare CPU main control module automatically. Control decisions and the transfer of the software block diagram shown in Figure 4. 2, 2 CPU module synchronization as hot spare CPU stands ready, once the main CPU failure, the immediate access to the main control and a host CPU, therefore, the main CPU must keep their information passed to the hot spare CPU, while the hot standby CPU must keep track of changes in the main CPU, to keep pace with the main CPU, so that the two CPU modules when the transfer of control, disturbance-free switching. CPU module synchronization control block diagram shown in Figure 5. V. Conclusion
dual-CPU, with AB ControlLogix PLC controller of the salt furnace automated system, successfully run the end of 2001 Aluminum in China Henan branch, running well, to meet a pipeline of diaspore dissolution process of alumina production line requirements. Our experience is, ControlLogix dual CPU redundancy control the realization of the software is an economic and effective method, it costs to much, but can greatly enhance the reliability of the system. In addition, the pair of redundant control of the CPU, how to use Map command, only to have the main control over the CPU data Tongguo ControlNet over Transport to other control equipment, is worth further Yanjiu s. References:
[1] Allen-Bradley Logix5550 Controller User s Guide 1756-6.5.12 SEP 1999 [2] Allen-Bradley Software Output Switching Publication 1756-AP001A-US-E-December 1999