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Master Clocks: A Guide to Master-Slave Time Clock Systems

What is a Master Clock System?

A master clock is an electronic device that provides time synchronization signals to a number of slave clocks on a network. Typically, the master time clock maintains accurate time from a hardware clock source, such as GPS, GLONASS, Galileo or other sources of precise time.

GPS master time clock system synchronizing wall clocks, CCTV cameras, servers and workstations.

Slave Clocks

A slave clock is a hardware device that typically depends on a master clock to for accurate time. A number of slave clocks synchronize with a master clock to provide a display of accurate time. Slave clocks typically communicate on a clock network. The clock network can either be a simple wired serial network, a wired pulse signal or a more complex Ethernet network.

Types of Clock Network

Originally, many master clock systems used an impulses generated by the master clock to advance and synchronize slave clocks. Impulse driver has generally been superseded by serial or Ethernet network clocks.

Serial clocks utilize a RS422 or RS485 transmission system. Timing information is broadcast along a 2 or 4 core cable to clocks that are usually daisy-chained.

The latest clocks utilize IP based ethernet networking. Ethernet networks allow clocks to be configured from a central point using a standard PC. It also allows much more flexibility of cabling installation. Standard networking devices and infrastructure can be used for the network.

All TimeTools master and slave clocks use Ethernet networking. Additionally, Power-over-Ethernet (PoE) has provided even more installation flexibility. PoE provides both data and power on a single standard ethernet cable. No mains spur is required where clocks are located – significantly lowering installation costs.

Sources of Accurate Time

There are a number of global and national hardware clock references. Global time references are generally satellite based – such as GPS, GLONASS and Galileo. While national time references are often radio based – such as MSF (UK), DCF (Germany) and WWVB (USA). These time references can be used by master clock systems as a source of accurate time.

The GPS system is operated by the US government, it is a subscription-free system that provides global navigation and timing services. GLONASS is a similar service operated by the Russian government. While Galileo is the new civilian satellite based navigation and timing system operated by the European Union, due to be fully operational by 2019.

Radio time references are often constrained by national boundaries. The MSF signal is operated for the UK government and is available throughout the UK and Western Europe. The DCF-77 transmitter is located in Frankfurt, Germany, and serves much of Western and Central Europe. The WWVB transmitter is located in Colorado and serves the North American continent.

Satellite time references are more accurate than radio sources and can be received globally. They are generally regarded as superior sources of time.

TimeTools GPS Master Clocks

TimeTools has a range of GPS and Multi-GNSS referenced master clock models. They synchronize slave clocks using the Network Time Protocol (NTP) over an IP Ethernet network. They can also be used to synchronize servers, workstations and network infrastructure.

TimeTools T300 GPS Master Clock

TimeTools T100 is a low-cost, high-performance master clock housed in a compact enclosure.

The T300 GPS master time clock is housed in a 1U high, rack-mountable enclosure.

The T550 is a dual LAN, Multi-GNSS master clock with TCXO oscillator. The device can receive timing information from multiple satellite systems – GPS, GLONASS, Beidou and Galileo. The T550 also has a high-precision TCXO oscillator to maintain accurate time in the event of loss of satellite signals.

TimeTools NTP Synchronized Slave Clocks

TimeTools have a range of slave clocks that synchronize to a master clock using the NTP protocol. Available in 4 and 6 digit and analog models. The digital display models have 100mm (4 inch) high digits, viewable from up to 50 m. The analog clock is available with a 300 mm (12 inch) clock face.

Analog and Digital Slave Clocks Provide an Accurate Time Display

The slave clocks connect to a master over an IP Ethernet network. Each clock has a RJ45 network connector at the rear. All models are Power-over-Ethernet (PoE) devices. PoE allows clocks to be installed with only a single data cable required to be run to the clock. A mains spur is not required where the clock is located. PoE simplifies installation and reduces installation costs.

Related Articles

Choosing a Master Clock
A Guide To GPS Master Clocks

Additional Resources
Time Systems and Dates – GPS Time
Time References in GNSS