描述
控制系统冗余设计的目的:系统运行不受局部故障的影响,而且故障部件的维护对整个系统的功能实现没有影响,并可以实现在线维护,使故障部件得到及时的修复。冗余设计会增加系统设计的难度,冗余配置会增加用户系统的投资,但这种投资换来了系统的可靠性,它提高了整个用户系统的平均无故障时间(MTBF),缩短了平均故障修复时间(MTTR),因此,应用在重要场合的控制系统,冗余是非常必要的。
二个部件组成的并联系统(互为冗余)与单部件相比,平均无故障时间是原来的1.5倍。系统的可用性指标可以用两个参数进行简单的描述,一个是平均无故障时间(MTBF),另一个是平均修复时间(MTBR)。系统的可用性可用下式表示:
系统可用性=MTBF/(MTBF+MTBR)
当可用性达到99.999%时,系统每年停止服务的时间只有6分钟。
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