描述
根据统计资料表明：在PLC控制系统的故障中，CPU占5%，I/O接口占15%，输入设备占45%，输出设备占30%，线路占5%。前二项共20%故障属于PLC的内部故障，它可通过PLC本身的软、硬件实现检测、处理；而其余80%的故障属于PLC的外部故障。因此，PLC生产厂家都致力于研制、发展用于检测外部故障的专用智能模块，进一步提高系统的可靠性。
3COM SuperStack II 3900 3C39036 36 Port Switch 4-PACK
3Com Switch 4005 (3C16831) with installed cards, power
3COM 3C16985B SuperStack 3 Switch 3300 XM 24 ports SALE
3COM Base Line 48 Port Switch 2848-SFP Plus (3C16486)
NEW IN BOX – 3Com IntelliJack Gigabit Switch NJ2000
NEW IN BOX – 3Com IntelliJack Gigabit Switch NJ2000
3COM 3C16472 Baseline Switch 2126-G RJ-45
3Com Baseline Switch 2024 – switch – 24 ports
3COM SuperStack 3 Switch 4200 26-Port 3C17300A
3Com Superstack 3 Switch 4400 SE – 3C17206-US
3COM 3C17302A Superstack 3 switch 4200 50-Port
