（3）高可靠性由于控制系统的可靠性日益受到人们的重视，一些公司已将自诊断技术、冗余技术、容错技术广泛应用到现有产品中，推出了高可靠性的冗余系统，并采用热备用或并行工作、多数表决的工作方式。S7400 PLC即使在恶劣、不稳定的工作环境下，坚固、全密封的模板依然可正常工作，在操作运行过程中模板还可热插拔。
level, the Freelance 800F system can be controlled by
It consists of a number of process control stations connected to I/O units. you can choose this
Some process stations are in redundant mode (CPU redundancy, fieldbus module redundancy
redundant) or non-redundant mode. Modular pluggable input/output modules
Blocks are freely selected and used according to the type and number of system process signals.
AC800F controller connects remote I/O or field device via fieldbus
ready.
system communication
Communication between operator level and process control level using TCP/IP
Protocol system bus (based on Ethernet), you can choose different
transmission medium such as AUI, twisted pair, fiber optic or coaxial cable.
Freelance OPC server for connecting to
