PLC redundancy can be divided into software redundancy and hardware redundancy. Hardware redundancy requires different hardware models and connection methods, but there are no special requirements for software.
Programmable logic controllers (PLCs) are widely used as controllers in industrial automation systems, and with the development of technology, redundant systems are established to further improve system reliability. At present, there are many classification methods for redundancy, and there are two types of PLC redundancy methods, namely soft redundancy and hard redundancy. Siemens has provided solutions for both software and hardware redundancy. Based on hard redundancy, the reliability is high, but the cost of building the system is also high. Soft redundancy based on S7-300 or S7-400 is a low-cost and reliable solution. At present, soft redundant systems have been widely used in industrial control engineering such as metallurgy, transportation, power, chemical industry, and sewage treatment. However, there is still no systematic research on the performance of soft redundancy.
