| 摘要 |
PROBLEM TO BE SOLVED: To realize a system of a high working rate by directly controlling a common I/O device from either of two PLCs limited as the objects of duplex operation so as to switch the charge of majority decision at the time of generating a fault. SOLUTION: The programmable logic controllers PLC 1 and 2 are provided with the control function of the I/O device 4 as the objects of duplex operation, respectively consist of CPUs 11 and 21, communication modules 12 and 22, I/O interfaces 13 and 23 and power sources 14 and 24 and is combined by way of back planes 15 and 25 through a parallel bus. PLC 3 is the object of majority decision with PLCs 1 and 2, consists of CPU 31, a communication module 32 and a power source 33 and combined by way of a back plane 34. In addition to transferring normal data, three PLCs 1, 2 and 3 execute parallel off processing at the time of generating a fault and double row processing at the time of restoring a fault and dynamically switches the role charge of PLCs 1, 2 and 3 as an operation station and a monitoring station. |
