NTP Clock Systems and Networked Time Displays

Organisations need an accurate display of time. Schools, Colleges and Universities need to ensure lessons start at the correct time. Also, Companies need to ensure that meetings commence at an agreed time. Many organisations also need to accurately log events. Hospitals may need to know exactly when a patient requires medicine or to log the time of events associated with patients.

Time and attendance systems and clocking systems need to have a time display that is synchronised to the systems time, so that employees are clocking in and out at the correct time. Access control systems that restrict access at certain times during the day may need to have an accurate display of time, so that users can accurately see when access is allowed.

People need an accurate display of time so that they can be where they need to be at the correct time. Everyone is working in sync !

Whether it is to ensure meetings or lessons start at the correct time or to accurately log the time of events, a NTP clock source will provide an accurate display of time.

Ethernet Networked Synchronized Analog and Digital Time Displays

How They Work

A NTP clock display resides on an Ethernet network just like any other networked device. They have an RJ45 network connector at the back which allows the clock to communicate to a time reference over the network. Periodically, the clock will request accurate time from the time reference in order to correct any drift in its internal local clock. The clock will display its synchronised local time to users on a large analogue or LED display on the face of the clock.

Clocks utilise the Network Time Protocol (NTP, SNTP) to obtain accurate time from a NTP time server. NTP is a standard protocol for communicating time between networked devices.

In the even that the time reference cannot be contacted to obtain accurate time, the clock will continue to display the free-wheeling time available from its internal local clock. It will also illuminate a service LED, indicating that the clock has lost synchronisation.

A Time Reference For Synchronisation

The clocks utilise the NTP protocol to obtain time from a networked time server. The time server is an accurate time reference. A number of sources of time can be used.

There are a large number of completely free to use internet based time references. However, in this instance, the networks on which the clocks reside need to have access to the internet. This may be undesirable due to the security concerns of leaving ports open in the network firewall to allow communication.

Alternatively, the clocks can synchronise to a Windows or Linux \ Unix based server. The clocks will however only be as accurate as the time on the server itself. Occasionally, this can be beneficial. In access control or time and attendance and clocking machine applications, it can be a requirement for the clocks to display the same time as the clocking system itself. In this manner everything is in sync.

Generally, the preferred option is to synchronise the clocks back to a local time server. The local NTP time server obtains and maintains accurate time obtained from a GPS time reference. This option has the added advantages of security and control. The time server can also be used to synchronise other time critical applications and devices, such as server and workstations, CCTV and DVR systems and network infrastructure.

Summary

NTP clock synchronization provides an organisation with a reliable, accurate and legally traceable display of time. Every clock, whether in the basement or on the top-floor shows the same accurate time.

Additional References

http://www.ntp.org/ntpfaq/NTP-s-sw-clocks-quality.htm
http://en.wikipedia.org/wiki/Network_Time_Protocol
http://www.freebsd.org/doc/handbook/network-ntp.html

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