A tracing apparatus communicably connected to a programmable logic controller (PLC) that inputs and outputs a signal based on a ladder program, includes a constituent element setting unit configured to set a plurality of constituent elements to be traced among the constituent elements of the ladder program, a tracing data acquisition unit configured to acquire tracing data indicating a signal state of the constituent element at a specified timing, at a predetermined sampling cycle, a section detection unit configured to detect a sampling cycle section in which two or more of the acquired tracing data corresponding to the constituent elements simultaneously change, a change sequence calculation unit configured to calculate change sequence of signals of the constituent elements simultaneously changing in the detected sampling cycle section, and a change sequence output unit configured to output the calculated change sequence of the signals of the constituent elements.

A tracing apparatus communicably connected to a programmable logic controller (PLC) that inputs and outputs a signal based on a ladder program, includes a constituent element setting unit configured to set a plurality of constituent elements to be traced among the constituent elements of the ladder program, a tracing data acquisition unit configured to acquire tracing data indicating a signal state of the constituent element at a specified timing, at a predetermined sampling cycle, a section detection unit configured to detect a sampling cycle section in which two or more of the acquired tracing data corresponding to the constituent elements simultaneously change, a change sequence calculation unit configured to calculate change sequence of signals of the constituent elements simultaneously changing in the detected sampling cycle section, and a change sequence output unit configured to output the calculated change sequence of the signals of the constituent elements.

A numerical controller includes a programmable controller that performs input and output of a signal based on a ladder program and performs control of a machine based on an NC program. The numerical controller includes a first table associating the function used for control of the machine, an input signal, and an output signal and a second table associating the input signal, the output signal, and a signal in a dependent relation with the input signal and the output signal. Based on a function code of a function commanded by a block of the NC program that is preread, the numerical controller refers to the first and the second tables, identifies a signal to be subjected to automatic trace, and performs trace.

A numerical controller includes a programmable controller that performs input and output of a signal based on a ladder program and performs control of a machine based on an NC program. The numerical controller includes a first table associating the function used for control of the machine, an input signal, and an output signal and a second table associating the input signal, the output signal, and a signal in a dependent relation with the input signal and the output signal. Based on a function code of a function commanded by a block of the NC program that is preread, the numerical controller refers to the first and the second tables, identifies a signal to be subjected to automatic trace, and performs trace.

A controller stores link information linking a predetermined event to a variable associated with the event. The controller stores first log information in association with time information into a memory in response to occurrence of the predetermined event. The first log information includes information about the event, and a current value of a predetermined variable associated with the event included in the link information. The controller stores second log information in association with time information into a memory in accordance with a predetermined period. The second log information includes information about a value of the predetermined variable. An information processing device obtains the link information from the controller, and displays information indicating the variable associated with an event indicated by the first log information onto the monitor-based on the link information and the second log information.