Clock synchronization of control systems

The Siemens SINUAT S7 system is equipped with a GPS receiver interface, and clock synchronization for the entire system can be achieved through proper settings.

Clock synchronization technology is quite important in control systems. On more than one occasion, DCS operator stations have failed due to the DCS clock being out of sync with the GPS clock. I am not familiar with more complex technical issues either; I only know that GPS time synchronization is a relatively mature technology that is widely used internationally. High-precision GPS synchronized clocks provide standard time information to the network time synchronization module via an RS interface, in the form of time data and second pulse signals, with these time synchronization signals being synchronized to Coordinated Universal Time (UTC). The NTP server software transforms the module into a standard NTP network time server, enabling it to synchronize WINDOWS 9X/NT workstations on the network through client software. Operating systems such as WINDOWS 2000/XP/2003, LINUX, UNIX, and SUN SOLARIS, as well as Cisco routers and switches, can automatically synchronize with the network time server using their built-in NTP/SNTP client software, thereby enabling network-based time synchronization. The system consists of three components: a GPS antenna, a network-synced clock (a GPS sync clock equipped with a network time synchronization module), and client software (client software is built into most operating systems). When connecting the network interface of a network synchronization clock to a client, use an Ethernet cable with RJ-45 connectors on both ends; the wiring standard for these connectors is EIA/TIA 568B. Such a cable is known as a parallel cable or straight-through cable, and it can be used to connect computers, Cisco routers and switches, NICs (Network Interface Adapters), and hubs. This device synchronizes all computers, controllers, and other devices in a network using the NTP protocol to enable network-based time synchronization. Thanks to its high accuracy in timing and the fact that there are no restrictions on the transmission distance, it is now widely used in various industries, especially in mobile communications.

In our various control and monitoring systems, such as CENTUM-CS, TRICON, BENTLY3500, and S8000, etc., the issue of system clock synchronization is not taken into account; the time displayed on the trend charts of different systems varies, which prevents an accurate reflection of the sequence of events that lead to a particular situation, thereby hindering analysis and decision-making. Is there a feasible solution considering our actual situation?

Shanghai Ruicheng’s K00 series of high-precision GPS synchronized clocks deliver standard time information to the network time synchronization module via an RS-232 interface, providing both time data and second pulse signals; these time synchronization signals are synchronized with Coordinated Universal Time (UTC). The NTP server software transforms the module into a standard NTP network time server, enabling it to synchronize WINDOWS 9X/NT workstations on the network through client software. Operating systems such as WINDOWS 2000/XP/2003, LINUX, UNIX, and SUN SOLARIS, as well as Cisco routers and switches, can automatically synchronize with the network time server using their built-in NTP/SNTP client software, thereby enabling network-based time synchronization. The system consists of three components: a GPS antenna, a network-synced clock (a GPS sync clock equipped with a network time synchronization module), and client software (client software is built into most operating systems). Note: When connecting the network interface of the network synchronization clock to a client, use an Ethernet cable with RJ-45 connectors on both ends. The wiring standard for these connectors is EIA/TIA 568B; such a cable is known as a parallel cable or straight-through cable. It can be used to connect computers, Cisco routers and switches, NICs (Network Interface Adapters), and hubs. This device synchronizes all computers, controllers, and other devices in a network using the NTP protocol to enable network time synchronization. Thanks to its high timing accuracy and the fact that there are no limits on the transmission distance, it is now widely used in various industries. In today’s rapidly developing internet era, tasks such as the reading and storage of network data files, online ordering and payment systems, e-commerce systems, B2B systems over the internet, as well as the storage and maintenance of databases – along with many other essential internet applications – all rely on high-precision network time synchronization modules. These modules combine high-speed, large-capacity network interfaces with user interfaces based on the Internet, and they support a variety of network protocols; they are thus of great significance for creating truly synchronized network environments. This product is a true NTP network time server that is at the leading level in China in terms of technology, having reached the technical standards of similar products abroad. Most domestic manufacturers use the SNTP protocol for network time synchronization interfaces, or convert serial ports to RJ45 interfaces; this approach simply cannot ensure accuracy in time synchronization. Moreover, separate software for time synchronization must be developed for different operating systems in order to achieve network-based time synchronization, which results in significant limitations and inaccuracies in such systems, and they fail to meet the requirements of true network time synchronization. Supported protocols: ·NTP v2, v3 & v4 (RFC1119& 1305) ·NTP broadcast mode ·SNTP Simple Network Time Protocol (RFC2030) ·MD5 Authentication (RFC 1321) ·Telnet (RFC854) ·FTP (RFC959) ·DHCP (RFC2132) Network interface: 10/100M adaptive Ethernet interface ； Typical time synchronization method for HOLLiAS DCS (HOLLiAS MACS system): *The GPS antenna receives time signals ； ＊Sent from the serial port to the FM197 timing hub ； ＊The FM197 time synchronization hub sends data to the system time server ； * The time server broadcasts synchronization packets over the network at regular intervals or when the local time changes ； ＊Clients set to synchronize with a time server will change their local system time after receiving the time synchronization packet ； * When the client starts running the system, it requests time synchronization from the time server. Timing characteristics * The timing transmission and reception in the control system are primarily carried out via the network ； * For critical SOE fast clock synchronization, second pulses are primarily generated via hardwired connections, ensuring that the SOE clock error between stations remains ≤1ms ； ＊ A time synchronization hub is used to receive GPS clock signals, thereby synchronizing the DCS clock server, the SIS system, and other devices at the same time ； ＊ Unique setting for the network time synchronization clock server. Typical timing method for ABB’s DCS: One part is connected to the AC800F controller (where timing can be performed directly via IRIG-B code), while another part is connected to the network via NTP to enable timing for systems such as the SIS and engineer stations. Shanghai Ruicheng Electrical Co., Ltd. Beijing Office Phone: 13811068285 This post was last edited by Mobei Yihai on 2009-4-17 16:38]

Power system protection systems all come equipped with GPS synchronization systems, such as those from South Rui and Beijing Sifang.

Currently, the clock synchronization solutions provided by major DCS manufacturers are based on the Ethernet protocol. Taking the Windows platform as an example, it is sufficient to spend around 2,000 RMB on a clock source to synchronize the domain controllers in the Windows “domain”; thereafter, all remaining nodes can be synchronized by being added to this “domain”. This approach is both the most economical and the most reasonable. :lol

However, this method does not have sufficient precision, as all protocols are SNTP, and the time accuracy of each station in the network is 1 second. For high-demand applications, specialized clock protocols are also required

Clock synchronization at the operation station and control station has been done; no issues have arisen with GPS time synchronization.

The NTP protocol is used for clock synchronization.

In our plant, one set of Hilscher DCS systems has asynchronous clocks, which prevents the trend charts on some operation stations from being visible