KR-20260067980-A - INDICATING CLOCK DRIFT OF AN INTERNAL CLOCK IN A SENSOR DEVICE

KR20260067980AKR 20260067980 AKR20260067980 AKR 20260067980AKR-20260067980-A

Abstract

A method for indicating clock drift of an internal clock included in a sensor device comprises: capturing a first data frame by a sensor device (s302); associating the first data frame with a first time point indicating the time point of an internal clock when the first data frame is captured by the sensor device (s304); receiving time synchronization data by a sensor device through a network protocol for clock synchronization (s306); determining a reference time point indicating the time point of a reference clock when the first data frame is captured by the sensor device using the time synchronization data (s308); determining an offset between the first time point and the reference time point by the sensor device (s310); and, when the offset exceeds a threshold offset, associating the first data frame with data indicating the offset by the sensor device (s312).

Inventors

안드레아스 뱅크
크리스티안 스톰

Assignees

엑시스 에이비

Dates

Publication Date: 20260513
Application Date: 20251002
Priority Date: 20241106

Claims (15)

A method for indicating clock drift of an internal clock included in a sensor device, wherein the method comprises: A step of capturing a first data frame by the sensor device; A step of associating the first data frame with a first time point indicating the time point of the internal clock when the first data frame is captured by the sensor device; A step of receiving time synchronization data by the sensor device through a network protocol for clock synchronization; A step of determining, by the sensor device, a reference time point indicating the time of the reference clock when the first data frame is captured, using the time synchronization data above; A step of determining an offset between the first point in time and the reference point in time by the sensor device; and A method comprising the step of associating data representing the offset with the first data frame by the sensor device when the offset exceeds a threshold offset.
In paragraph 1, The sensor device is a network camera, the first data frame is a first image frame, and the step of associating the first image frame with data representing the offset by the network camera is A method comprising the step of adding graphic data visualizing data representing the offset to an overlay associated with the first image frame.
In paragraph 1, A method comprising the step of associating the first data frame with data representing the offset by the sensor device, the step of adding the data representing the offset as first metadata associated with the first data frame.
In paragraph 3, The first metadata associated with the first data frame is, A method provided as at least one of data stream metadata, metadata added to the header of the first data frame, or a separate metadata stream.
In paragraph 3, A step of determining a signature using sensor data of the first data frame and the first metadata; and A method further comprising the step of incorporating the signature into a record including the first data frame and the first metadata.
In paragraph 1, The step of associating the first data frame with the first time point by the sensor device is, A method comprising the step of adding the first time point as second metadata associated with the first data frame.
In paragraph 1, The sensor device is a network camera, the first data frame is a first image frame, and the step of associating the first image frame with the first time point by the network camera is A method comprising the step of adding graphic data visualizing the first time point to an overlay associated with the first image frame.
In paragraph 1, A step of continuously capturing data frames by the sensor device; For each captured data frame, a step of associating an additional time point, indicating the time point of the internal clock at the time the captured data frame is captured, with the captured data frame by the sensor device; While continuously capturing the above data frames, at predetermined intervals, A step of receiving time synchronization data by the sensor device through a network protocol for clock synchronization; A step of determining by the sensor device an additional reference point indicating the point in time of the reference clock when the most recently captured data frame is captured, using the time synchronization data above; A step of determining an additional offset between the additional point in time and the additional reference point in time associated with the most recently captured image frame; and A method further comprising the step of associating data representing the additional offset with the most recently captured data frame when the additional offset exceeds a threshold offset.
In paragraph 1, A method further comprising a step of adjusting an internal clock to reduce the offset, wherein the magnitude of the adjustment is limited by the specifications of a network protocol for clock synchronization.
In paragraph 1, A method further comprising the step of determining the exact time at which the first data frame was captured using data representing the first time point and the offset in a device separate from the sensor device.
In Paragraph 10, In a device separate from the above sensor device, A second time point representing the time of the internal clock of the sensor device at the time when the second data frame is captured, as a second time point associated with the second data frame, and Data representing an offset associated with the first data frame A method further comprising the step of determining the exact time at which the second data frame was captured using the above.
A non-transient computer-readable storage medium having stored instructions for implementing a method according to any one of claims 1 to 11, and enabling the method to be performed when said instructions are executed on one or more devices having processing capabilities.
A sensor device configured to indicate clock drift of an internal clock included in the sensor device, wherein the sensor device Configured to capture a first data frame; It is configured to associate the first data frame with a first time point indicating the time point of the internal clock when the first data frame is captured; Configured to receive time synchronization data via a network protocol for clock synchronization; It is configured to determine a reference time point indicating the point in time of the reference clock when the first data frame is captured, using the time synchronization data above; It is configured to determine an offset between the first point in time and the reference point in time; and A sensor device configured to associate data representing the offset with the first data frame when the offset exceeds a threshold offset.
A system comprising a sensor device according to Paragraph 13 and a device separate from said sensor device, A system configured such that the above separate device uses data representing the first time point and the offset to determine the exact time point at which the first data frame was captured by the sensor device.
In Paragraph 14, A device separate from the above sensor device A second time point associated with a second data frame, representing the time of the internal clock of the sensor device when the second data frame is captured; and Data representing an offset associated with the first data frame A system further configured to determine the exact time at which a second data frame is captured by the sensor device using the above.

Description

Method for indicating clock drift of an internal clock in a sensor device The present invention relates to a networked system and a time synchronization protocol, and in particular to a method, apparatus, and system for indicating clock drift of an internal clock of a sensor device. In modern networked environments, sensor devices such as video cameras, microphones, and other network-based sensor devices rely heavily on maintaining accurate time to ensure synchronized operation. These devices often utilize network protocols for clock synchronization that allow their internal clocks to be regularly adjusted to a central time reference. Such synchronization is critical for applications that rely on precise timestamps, such as video surveillance and event monitoring. One widely used protocol for clock synchronization is the Network Time Protocol (NTP). NTP ensures that the internal clock time remains accurate over time by having the device periodically adjust its clock frequency to gradually align with the time of an NTP server (i.e., achieve the same time value and average time progression as the NTP server). NTP and other similar protocols often have specific rules regarding how quickly a device can adjust its clock after a discrepancy is detected in order to prevent abrupt time changes. For example, if a device is connected to a synchronization server, it may periodically perform small adjustments that gradually correct the internal clock over time to align it with the server's time using mechanisms such as slew adjustment. This causes problems when a device temporarily loses its connection to the synchronization server due to network issues, server downtime, or other interruptions. During these offline periods, the sensor device's internal clock may begin to gradually deviate from the accurate time provided by the server. This drift can occur if the sensor's real-time clock (RTC) malfunctions, losing precision or accuracy over time. This issue is particularly severe in applications where precise time alignment is critical, such as video surveillance. For example, in a multi-camera configuration, if one or more cameras experience clock drift while disconnected from the synchronization server, the clocks of each camera may continue to display different times even after reconnection. Therefore, improvement is required in this context. In addition to the foregoing, further objects, features, and advantages of the present invention may be more clearly understood through the exemplary and non-limiting detailed description of embodiments of the present disclosure with reference to the accompanying drawings, where the same reference numerals are used for similar elements, and where: FIG. 1 illustrates a graph relating to clock drift in a sensor device according to embodiments; FIG. 2 illustrates a system configured to display clock drift in a sensor device according to embodiments; FIG. 3 illustrates a flowchart of a method for displaying clock drift of an internal clock included in a sensor device according to embodiments. In time-sensitive applications such as video surveillance, event detection, and multi-sensor systems, maintaining accurate time synchronization between devices is critical. Sensor devices often rely on internal clocks that can drift over time relative to the reference clock provided by a Network Time Protocol (NTP) server. This drift can lead to significant time discrepancies in recorded data if time synchronization is not possible, which can affect event reconstruction, forensic analysis, and multi-sensor synchronization. To solve these problems, the present disclosure provides a method and system for managing clock drift in a sensor device by including clock drift information in recorded data. The method comprises capturing a data frame by the sensor device and associating an offset between an internal clock and a reference clock with the data frame when the drift exceeds a predefined threshold. As described below in relation to FIGS. 1 to 3, the techniques described herein can be used to indicate clock drift after a period during which the sensor device has lost connection with the reference clock, thereby enabling accurate reconstruction of event timing even after a period during which synchronization was temporarily impossible. FIG. 1 illustrates a graph (100) regarding clock drift in a sensor device, where the vertical axis (112) represents the clock offset or drift (both positive (+) and negative (-)) in seconds, and the horizontal axis represents the time (104) of the reference clock (the reference clock is clearly fully synchronized with time and has no offset). The dashed line (102) represents the time of the internal clock of the sensor device, and said internal clock experiences drift over time relative to the time (104) of the reference clock (indicated by the vertical axis (112)). At any point in time, the vertical distance between the time (102) of the internal clock and the time