PEVENTING DEVICE FOR ERRONEOUS CONTROL OF CONTROLLER

PURPOSE:To prevent the erroneous control due to a fault of an input/output device, by carrying out all inputs and outputs with binary signals along with a number of input/output points, receiving the control command input at an internal logical memory and delivering the internal arithmetic result to the control device via an external output relay. CONSTITUTION:A control command input 2, if exists, is received at a control command input DI point 3 and supplied to a logical memory A. The memory A is set at logic ''1'' with the input 2 to drive the 1st control output DO point 4 and then to actuate the 1st control output relay 5. The state of the relay 5 is fetched into a DI point 6, and the coincidence and dissidence are always monitored by a comparison monitoring circuit D between the points 4 and 6. At the same time, a timer B is actuated by the logic ''1'' output of the memory A, and the counting is started for the lapse of time. When no fault arises at a constant comparison monitoring circuit E for the 2nd control output relay, a constant detecting circuit F for an application suppressing relay and a control machinery detecting circuit G respectively until the lapse of the time set at the timer B, no suppression signal H is delivered from an input/output fault deciding circuit H.