Controller, control program, and control system

A non-transitory computer-readable storage medium storing a control program that is executable by a controller for performing a control operation associated with a control target, the controller being electrically connected to at least one function unit through a data transmission path with a communication interface, the control program causing the controller to perform operations comprising:

• writing an observation value obtained through the function unit into a database;
• obtaining a delay time taken from when a signal indicating the observation value is input into the function unit to when data representing the observation value becomes usable in the controller, and storing information indicating the obtained delay time;
• and
• determining a time at which the signal indicating the observation value has appeared based on the information indicating the obtained delay time, wherein
• the delay time comprises a first delay time that does not vary over time and a second delay time that varies over time,
• the communication interface comprises a counter and the function unit comprises a counter, and the counters are time-synchronized with each other,
• the second delay time comprises a delay time that varies over time depending on a difference between counter values indicated by the counters,
• the writing comprises associating the observation value with the time at which the observation value becomes usable in the controller, and writing the observation value and the time into the database, and
• the determining comprises correcting the time associated with the observation value read from the database based on the information indicating the obtained delay time to determine the time at which the signal indicating the observation value has appeared.

A control system, comprising:

• a controller configured to perform a control operation associated with a control target;
• and
• at least one function unit electrically connected to the controller through a data transmission path with a communication interface of the controller,
• wherein:
• the controller is configured to perform operations comprising:
• operation as a writing unit configured to write an observation value obtained through the function unit into a database;
• and
• operation as a delay obtaining unit configured to obtain a delay time taken from when a signal indicating the observation value is input into the function unit to when data representing the observation value becomes usable in the controller, and store information indicating the obtained delay time;
• the delay time comprises a first delay time that does not vary over time and a second delay time that varies over time;
• the communication interface comprises a counter and the function unit comprises a counter, and the counters are time-synchronized with each other,
• the second delay time includes a delay time that varies over time depending on a difference between counter values indicated by the counters;
• the controller is further configured with the program to perform operations comprising operation as a time determination unit configured to determine a time at which the signal indicating the observation value has appeared based on the information indicating the delay time obtained by the delay obtaining unit;
• and
• the controller is further configured with the program such that:
• operation as the writing unit comprises associating the observation value with the time at which the observation value becomes usable in the controller, and writing the observation value and the time into the database;
• and
• operation as the time determination unit comprises correcting the time associated with the observation value read from the database based on the information indicating the delay time obtained by the delay obtaining unit to determine the time at which the signal indicating the observation value has appeared.