| 摘要 |
PURPOSE:To safely operate a control system, by detecting abnormalities of all power source devices and, after confirming that the power source devices are normal by a CPU, checking operations of the CPU, process input section, and process output section and, only when each of them is normal, impressing electric power upon the process output section. CONSTITUTION:When power supply is turned on, respective power source devices 2-4 rise and electric power is supplied to each section through each power supply line. A failure monitoring circuit 5 fetches signals indicating the normal state of each power source device 2-4 and produces the normal signal of the power source devices 2-4 at an AND circuit 55. The power source normal signal is sent to a CPU11 through a signal line 111 and an indicator 58 is turned on. Upon arriving the power source normal signal at the CPU11, the control section 1 of a programmable controller executes an initial process. As a result, the CPU11 makes self checking and, after the CPU11 accesses a process input section 12 and process output section (PO) 13 and confirms that they are normal, sends a system normal signal to the failure monitoring circuit 5. The AND of the system normal signal and the power source normal signal is taken at an AND circuit 56 and a relay 51 is driven and, in addition, a system normal indicator 57 is turned on. |
