What are the working principles of the metro clock system?

Feb. 05, 2026

The metro clock system is a key component of the metro's low-voltage power supply system. Its primary function is to provide standardized time signals for OCC dispatchers, station staff, maintenance personnel, office workers, and passengers, while also supplying synchronized clock signals to other subsystems. So, how much do you know about the working principles of this clock system? Let's dive in and learn together!

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

1. Primary Master Clock

Located in the control center, it receives the standard time signal from GNSS, calibrates its own time accuracy, and transmits the precise time signal to the secondary master clocks and other communication subsystems in each station, depot, or parking lot through the transmission system.

2. Secondary Master Clock

The sub-clock is located in the communication equipment room of each station, depot and parking lot, which receives the time calibration signal from the primary master clock and drives the sub-clock of the station, depot and parking lot.

The primary master clock receives the signal from the satellite through the antenna, and the secondary master clock receives the signal from the primary master clock through the signal cable.

What are the differences?

The distinction between the two lies in the signal source, though they are fundamentally identical, differing only in functionality. In emergency situations, the secondary master clock can serve as the primary master clock by connecting to the antenna. Both systems share the same internal architecture, comprising a GNSS receiver, a Beidou satellite receiver, a signal processing unit, a conversion control module, a conversion module, and a system interface unit.

The time synchronization principle of the clock system: Under normal GNSS conditions, the master clock can be synchronized via GNSS.

GNSS

Global Navigation Satellite System (GNSS) is a medium-range circular orbit satellite navigation system, which includes 24 satellites operating in 6 geocentric orbital planes, 1 ground control station, 3 data injection stations, 5 monitoring stations and GNSS receivers as user terminals.

The above explains the working principles of subway clock systems.

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