What are the working principles of the subway clock system?

The subway clock system is one of the important subsystems of the subway's weak current system. Its main function is not only to provide unified standard time for OCC dispatchers, station staff, maintenance personnel, office staff, and passengers, but also to provide unified clock signals for other subsystems. So, how much do you know about the working principles of the clock system? Let's learn together!

The clock system is mainly composed of GNSS timing reference source, primary master clock, secondary master clock, sub-clocks, time distribution unit, network management equipment, power supply and system signal transmission cables, etc.

1. Primary Master Clock

It is located in the control center, receives the standard time signal provided by GNSS, calibrates its own time accuracy, and sends the precise time signal through the transmission system to the secondary master clocks and other communication subsystems in each station/vehicle depot/parking lot.

2. Secondary Master Clock

It is located in the communication equipment room of each station, vehicle depot, and parking lot. It receives the timing signal from the primary master clock and drives the sub-clocks in its own station, vehicle depot, and parking lot.

The signal of the primary master clock is received by the antenna from satellites, and the secondary master clock receives it through the signal cable from the primary master clock.

What's the difference?

The difference lies in the signal source, but there is no fundamental difference. It only shows a functional difference. In emergency situations, the secondary master clock can connect to the antenna and be used as the primary master clock. The internal structure of both systems consists of GNSS receiving unit, Beidou satellite receiving unit, signal processing unit, conversion control module, conversion module, and system interface unit.

The timing principle of the clock system - In normal circumstances, the master clock of the clock system can be time-synchronized by GNSS.

Global Positioning System

The Global Positioning System is a medium-range circular orbit satellite navigation system, which includes 24 satellites operating in 6 geocentric orbit planes, a main control station on the ground, 3 data injection stations, 5 monitoring stations, and GNSS receivers as users.