【2025 Control Systems】Methods for clock synchronization of DCS, SIS, and GDS, deviations, and implementation
Thread Content
This post was last edited by zhoudingshengs on 2025-6-16 06:35. Clock synchronization refers to keeping the clocks of all devices in a system in sync to ensure data accuracy and real-time performance. In DCS, SIS, and GDS, deviations in clock synchronization can lead to data inconsistencies, disrupted event sequencing, and system failures. Therefore, for these systems, the accuracy of clock synchronization is crucial. In modern industrial systems, DCS (Distributed Control Systems), SIS (Safety Instrumented Systems), and GDS (Data Acquisition Systems) play important roles, and their coordinated operation is crucial for the safety and efficiency of industrial production. However, due to the independent operation of various systems and the differences between different devices, deviations in clock synchronization may occur. DCS is a system used to monitor and control industrial processes, and it typically consists of various controllers distributed throughout the plant. In DCS, the clocks of various controllers need to be synchronized to ensure that they can carry out tasks in a predetermined sequence. If the clock synchronization deviation is too large, it may cause errors in data transmission between controllers, thereby having a negative impact on the control of the manufacturing process. SIS is a system used to monitor and control safety-related functions in industrial processes. In SIS, deviations in clock synchronization can lead to incorrect calculations of the activation timing for safety instruments, thereby preventing the timely detection of potential hazards. For example, in a situation requiring an emergency shutdown, if there is a deviation in clock synchronization within the SIS, it may prevent the safety instruments from activating within the specified time, thereby delaying the execution of the emergency shutdown. GDS is a system used for collecting and storing industrial process data. In GDS, deviations in clock synchronization can lead to inaccurate timestamps for data acquisition, thereby preventing the accurate recording of the chronological order of the data. This will have a negative impact on subsequent data analysis and fault diagnosis. Especially when it is necessary to conduct correlation analysis on data from different devices, deviations in clock synchronization can lead to data inconsistencies, making it difficult to draw accurate conclusions.
To address the issue of clock synchronization discrepancies among DCS, SIS, and GDS, the Network Time Protocol (NTP) or Precision Time Protocol (PTP) is typically used. NTP is widely used for clock synchronization in computer networks; by referencing the international atomic time standard, it enables the clocks of various devices to remain synchronized. PTP, on the other hand, is more suitable for industrial control systems; it offers higher precision and greater reliability, meeting the strict requirements for clock synchronization in industrial applications.
In addition to these protocols at the software level, hardware devices can also be of great help. Devices such as high-precision clock modules and clock synchronizers produce clock signals that are stable and accurate, which can effectively reduce synchronization errors. Of course, regularly calibrating and maintaining the clock is also essential; only in this way can the accuracy of clock synchronization be ensured.
In networks with more than 50 nodes, it is advisable to install clock synchronizers; the time synchronization accuracy of such synchronizers should be no lower than 1 ms, while their timekeeping accuracy should be no lower than 2 μs/min.
Section 5.3.7 of the \"Design Specifications for Petrochemical Distributed Control Systems\" (SH/T3092-2013) requires that DCS systems should not use external clock sources based on wireless communication. This is for the sake of ensuring the safety of control systems. Section 6.2.2 of the specifications requires that DCS systems must not use wireless networks; control systems and instrumentation devices that utilize wireless networks shall not be connected to the DCS network, as this is a measure taken to ensure the safety of control systems.
Section 9.2 of the \"Design Specifications for Distributed Control System Engineering\" (HG/T20573-2012) requires that communication systems should include a device clock synchronization system capable of receiving clock signals from the Global Positioning System (GPS).
Section 6.5 of the \"Design Specifications for Remote Monitoring and Data Acquisition Systems for Petrochemical Instruments\" (SH/T3181-2016) requires that SCADA systems be equipped with GPS clocks in the dispatch control center, and that the various nodes in the SCADA network be synchronized using clock synchronization software.
Whether to set up a GPS clock server to keep time in line with a certain time zone should be determined by the enterprise based on its nature and requirements. For gas transmission pipelines, a GPS clock server must be installed in the SCADA system; it needs to be synchronized with the time of a specific time zone in order to ensure consistency in the timing of the control systems throughout the pipeline, which helps to guarantee its safe operation. For ordinary chemical enterprises, it is sufficient to synchronize the clocks of various control systems to meet the requirements of production monitoring.
Clock synchronization for new projects is generally initiated by the enterprise or suggested by the design firm; the two parties work together to determine the appropriate solution. The design firm specifies the requirements in the specifications for various control systems, and the DCS integrator is responsible for implementing this.
In cases where the control system of an operational device does not have clock synchronization, it is advisable to communicate with the original supplier of the control system during device maintenance to add clock synchronization functionality to ensure smooth production.
The purpose of clock synchronization is to ensure consistency in time-stamped data within a system and between systems. In reality, absolute time is not necessary; relative time is sufficient, nor is it required to be exactly in line with the time in a specific region. DCS already has a time synchronization function built in. In practical applications, when a third-party computer device that requires time-stamped data recording needs to synchronize with the DCS, it is advisable to use the DCS to emit synchronization signals. For third-party devices that record data without time stamps, clock synchronization is not necessary.