Control device, time stamp modification method, computer program, and data structure

A time stamp modification method comprising:

• repeatedly executing correction processing of a local time provided by a local clock circuit in which the local time is capable of being synchronized with a network time, the correction processing executed at a first frequency;
• causing a storage unit to store a time correction amount for each iteration of the correction processing in a memory together with a first time stamp of the point in time at which a respective iteration of correction processing was performed;
• collecting a plurality of data elements related to a controlled object;
• storing the collected plurality of data elements in a database, with a second time stamp attached to each data element of the plurality of data elements, the second time stamp indicating for each respective data element, a point in time at which the respective data element was collected;
• extracting, from the database, data elements of the plurality of data elements corresponding to a period designated by a query directed to the database;
• and
• modifying, for each of the extracted data elements, the respective second time stamp based on the time correction amount of the iteration of correction processing to which a respective first time stamp and a respective second time stamp correspond, by:
• calculating a time deviation per unit time comprising an amount by which a difference between the local time and the network time changes per each unit of time, by dividing the time correction amount to which the respective first time stamp corresponds by:
• an operation interval;
• or an elapsed time between iterations of the correction processing;
• calculating a time modification amount, for modifying the respective second time stamp, by multiplying the time deviation per unit time by an elapsed time between a first time indicated by the respective first time stamp and a second time indicated by the respective second time stamp;
• and
• applying the time modification amount to the respective second time stamp.

A data storage system for a computer memory in a control device comprising:

• the computer memory;
• a local clock circuit;
• and
• a processor configured with a program to perform operations comprising:
• repeatedly executing correction processing of a local time provided by the local clock circuit in which the local time is capable of being synchronized with a network time, the local time comprising a time upon which time stamps are based, the correction processing executed at a first interval,
• wherein
• the data storage system comprises:
• a first portion of the computer memory in which a time correction amount for each iteration of the correction processing together with a first time stamp of a first point in time according to the local time, at which a respective iteration of correction processing was performed is stored;
• and
• a second portion of the computer memory in which a time-series database comprising a plurality of records are stored in association with respective indexes, wherein each of the records is organized according to a data structure comprising:
• a data element related to a controlled object of the device;
• a second time stamp assigned to the data element, the second time stamp indicating a time of the local clock circuit at which the data element was collected;
• and
• an identifier for identifying a value of correction processing of the second time stamp such that the second time stamp is modified according to the value of correction processing to correct errors in the local clock circuit,
• the processor is configured with the program to perform operations further comprising modifying the second time stamp by, for each data element:
• calculating a time deviation per unit time comprising an amount by which a difference between the local time and the network time changes per each unit of time, by dividing the identified value of correction processing by:
• an operation interval of the correction processing;
• or an elapsed time between iterations of the correction processing;
• calculating a time modification amount, for modifying the second time stamp, by multiplying the time deviation per unit time by an elapsed time between a first time indicated by the first time stamp and a second time indicated by the second time stamp;
• and
• applying the time modification amount to the second time stamp.