In the process of learning 300 and 400 systems, I came into contact with the concept of redundancy. 300 uses soft redundancy, but 400? It can be both soft redundancy and hard redundancy. The redundancy functions of the two are the same, but what is the difference?

1、 Concept

Generally speaking, soft redundancy is software redundancy. Software redundancy (SWR) is a software package, which can be applied to the control system that does not require high switching time of the main and standby systems, and needs to be installed

Hard redundancy refers to the physical hardware redundancy, which enables two sets of mutually redundant systems to carry out real-time data exchange and communication through synchronization module.

2、 The difference between the two

Hard redundancy is realized by synchronous optical cable and synchronous module, which does not need software package support.

2. The CPU models of the active and standby systems with soft redundancy can be different, for example, one is 300 and the other is 400; the CPU models of the active and standby systems with hard redundancy must be the same.

3. The data synchronization of soft redundancy is periodic synchronization; the data synchronization of hard redundancy is time synchronization.

3. In soft redundancy, when the main CPU is working, the standby CPU is warm standby, that is to say, when the main CPU is processing program components, the standby CPU will skip these programs, which can prevent inconsistency between the two program components, that is, the program on the standby station is always ready to take over the program for processing. Therefore, in the soft redundancy system, the switching time between the main system and the standby system is long, generally in seconds.

The main CPU and the standby CPU are both in run mode. The two CPUs process user programs synchronously. After the main station fails, the standby CPU can switch immediately. The processing of the two CPUs is closely coordinated, and the time is millisecond.

4. When the interface of DP slave station or PROFIBUS link fails, the main and standby CPU of soft redundancy will switch, while in the hard redundancy system, the main and standby CPU will not switch when the slave station fails.

5. Soft redundancy does not support IO redundancy, and IO redundancy can only be implemented in hard redundancy.

Note: only 400H can achieve hard redundancy in 400 system.

LQ: editor in charge

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