Nanjing airport is an important air transport hub, is a modern large airport. The airport has electronic bell 94, while construction of the departure system, flight information display system, broadcasting system, dispatching system, information security systems, building automation systems, security monitoring system, parking lot management system, call center system and other information systems, these systems are connected to each other through the interface of collaborative work, consistency time is very important. Through the construction of the clock synchronization system, the system will be unified clock calibration, for each system to lay a solid foundation for cooperation.
1, The application of the clock in the airport and the necessity of clock synchronization
The communication network of communication equipment or computer equipment time information (the date when) based on UTC (UTC) time limit deviation in a sufficiently small range (such as 100ms), this process is called synchronization time synchronization.
Airport departure system according to the time signal at the appointed time opening and closing check-in; FIDS flight information display at the specified time; broadcast system broadcast in time to remind the booking information to guide passengers; building automation system to control the lighting, air conditioning according to the time of opening and closing; command and dispatch system by time accurate airport information command department cooperative work; each picture in security monitoring system must record the time information; parking lot management system relies on the exact time charge parking fees; call center according to the time information to guide passengers; passengers and staff also need accurate time information.
An accurate clock system is an important basis for the normal functioning of the various production systems.
2, The realization of clock synchronization system
2.1 Function introduction
The star structure, set up a NTP server, receiving the standard time signals from GPS, set up a high precision clock, clock time for receiving signals from the NTP, and the clock signal through the transmission subsystem to each sub clock into / departing passengers and airport staff to provide a unified standard time. At the same time clock output (with millisecond signal) standard time signal to the NTP network time server, by the time the NTP web server through a computer network system to provide uniform time signal to the coordination of the airport terminal and the production of the business operation Department, the electromechanical system timing device and system clock synchronization.
2.2 clock system components
Composed of the clock system mainly consists of GPS receiver, clock, sub center clock, world clock, NTP server, transmission channel and management control computer.
2.2 NTP (network time) server
Network time server receives the GPS standard time information, and sends this information to the standard time clock. Network time servers can provide standard time information for networked computers over ethernet.
The GPS antenna is properly installed and standard time signal into the control center communication room, connected to the network time server back, turn on the power switch, the network time server to start work, after a period of time, the front panel display local standard time.
2.3 GPS clock
As the basic clock master clock of the whole clock system, it can receive standard time signal from the network time server, calibrate the time precision of its own, and the precise time allocated to each sub clock signal. The clock is the central part of the whole system, the stability of the work largely determines the reliability of the whole system, therefore, should fully consider the comprehensive factors of the realization of the system function and system reliability, the system design, configuration of the machine unit to pay, and between the main and auxiliary machine can realize automatic or manual switch. Standard time clock sending and receiving network time server through a standard RS422 interface signal. Network time server during normal operation, the signal will be used as the time base of the master clock; network time server fails, the master clock will be used for high stability crystal oscillator itself as the time reference. The master clock through a standard RS422 interface to the standard time signal clock sent after calibration, and the operating state information receiver Zi Zhong echo, and can be controlled by the clock work status information back to the monitoring terminal, displayed on the monitor computer. The master clock through the standard RS232 is connected to the monitoring computer interface, to achieve the monitoring of the main equipment of the clock system, and time control computer.