GPS time service system (13269065974)
The GPS time service system is a high-tech product for the computer, control device, etc. in the automation system. The GPS time service product obtains the standard time signal from the GPS satellite and transmits the information to the automation system through various interface types. Equipment that requires time information (computers, protection devices, fault recorders, event sequence recording devices, safety automation devices, telecontrol RTUs) can achieve time synchronization of the entire system.
The GPS time service system developed by Beijing Zhongxinchuang can be applied to military command systems and dispatch systems; time stamp servers in the financial industry; telecommunication network management systems, billing systems, distributed database servers, and railway dispatch systems, etc. all require LAN time synchronization. And strongly urges that there is a standard network time source for the entire system.
Foreword
With the rapid development of computer and network communication technologies, the era of digitization and networking of thermal power plant automation systems has come. This aspect provides a better platform for data exchange, analysis, and application among various control and information systems. On the other hand, it also puts forward higher requirements for the accuracy of various real-time and historical data time tags.
The use of an inexpensive GPS clock to unify the clocks of various plant-wide systems is the standard practice currently used in the design of thermal power plants. The master clock of the unit distributed control system (DCS), auxiliary system programmable logic controller (PLC), plant-level monitoring information system (SIS), and power plant management information system (MIS) in the power plant is obtained through an appropriate GPS clock signal interface. Standard TOD (year, day, hour, minute, second) time, and then according to the respective clock synchronization mechanism, the slave clock deviation within the system is limited to a sufficiently small range, so as to achieve the whole plant clock synchronization.
First, GPS clock and output
1.1 GPS clock
The Global Positioning System (GPS) consists of a group of satellites launched by the US Department of Defense in 1978. A total of 24 satellites operate in the six geocentric orbital planes, which are visible on Earth according to time and location. The number of satellites has been constantly changing from 4 to 11 stars.
The GPS clock is a receiving device that receives a low-power radio signal transmitted by a GPS satellite and calculates the GPS time by calculation. In order to obtain accurate GPS time, the GPS clock must first receive signals from at least four GPS satellites and calculate its own three-dimensional position. After the specific position has been obtained, the accuracy of the clock can be guaranteed by the GPS clock receiving only one GPS satellite signal.
As a standard clock for thermal power plants, our basic requirements for GPS clocks are: At least 16 satellites can be tracked at the same time, with the shortest possible cold and warm start-up times, back-up batteries, and high-accuracy, flexibly configurable clock outputs. signal.
1.2 GPS clock signal output
At present, there are mainly three types of GPS clock output signals used by power plants:
1.2.1 1PPS/1PPM output
This format outputs one pulse per second or per minute. Obviously, the clock pulse output does not contain specific time information.
1.2.2 IRIG-B output
IRIG (the Inter-Range Instrumentation Group of the United States) shares coding standards A, B, D, E, G, and H (IRIG Standard 200-98). Among them, IRIG-B encoding is most widely used in clock synchronization applications, and there are formats such as bc level offset (DC code) and 1 kHz sinusoidal carrier amplitude modulation (AC code). IRIG-B signal output one frame per second (1fps), each frame is one second long. One frame has a total of 100 symbols (100pps), each symbol is 10ms wide, and the binary 0, 1 and position flag bits (P) are represented by symbols of different positive pulse widths, as shown in Figure 1.2.2-1.