Abstract: An operation state display apparatus includes a counter for receiving input signals which respectively represent the individual operation states of a controlled object and for counting the duration time of at least one of the ON and OFF state of the input signal. A memory device is provided for memorizing the period of time lapse from an operation initiation reference time when the input signal goes from the OFF state to the ON state or vice versa. A display device is provided for displaying in the form of a time chart the operation state of the controlled object according to the data of the counter and of the memory device. The reference operation state of the controlled object can also be displayed on the display device.

Abstract: In a programmable logic controller in which the control sequence for a controlled-objective such as a machine tool is stored in a memory unit, and the controlled-objective is automatically operated in a predetermined sequence according to the control sequence stored in the memory unit; a display system is provided in which a sequence block obtained from the control sequence stored in the memory unit is displayed in the form of a sequence diagram, particularly, a sequence diagram which includes symbols of control elements such as relays. A necessary sequence block is automatically obtained from the control sequence and is displayed. This display system is capable of displaying the states of the control elements, such as the on-off states of relay contacts.

Abstract: A sequence control monitoring device is disclosed which receives from controlled-objects operated under a sequence control system signals independently representing the operating states of the individual controlled-objects. The monitoring device counts the time duration for which each input signal remains in its on or off state, compares the counted value with a preset value, and thus judges whether the operating state of the controlled-object is correct.