Category: chronology

Atomic Clocks Now Doubled in Precision

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As with the advance of computer technology that seems to exponentially increase in capability every year, atomic clocks too seem to increase dramatically in their accuracy year on year.

Now, those pioneers of atomic clock technology, the US National Institute of Standards Time (NIST), have announced they have managed to produce an atomic clock with accuracy twice that of any clocks that have gone before.

The clock is based in a single aluminium atom and NIST claim it can remain accurate without losing a second in over 3.7 billion years (about the same length of time that life has existed Earth).

The previous most accurate clock was devised by the German Physikalisch-Technische Bundesanstalt (PTB) and was an optical clock based on a strontium atom and was accurate to a second in over a billion years. This new atomic clock by NIST is also an optical clock but is based on aluminium atoms, which according to NIST’s research with this clock, is far more accurate.

Optical clocks use lasers to hold atoms still and differ to the traditional atomic clocks used by computer networks using NTP servers (Network Time Protocol) and other technologies which are based on fountain clocks. Not only do these traditional fountain clocks use Caesium as their time keeping atom but instead of lasers they use super-cooled liquids and vacuums to control the atoms.

Thanks to work by NIST, PTB and the UK’s NPL (National Physical Laboratory) atomic clocks continue to advance exponentially, however, these new optical atomic clocks based on atoms like aluminium, mercury and strontium are a long way from being used as a basis for UTC (Coordinated Universal Time).

UTC is governed by a constellation of caesium fountain clocks that while still accurate to a second in 100,000 years are by far less precise than these optical clocks and are based on technology over fifty years old. And unfortunately until the world’s science community can agree on an atom and clock design to be used internationally, these precise atomic clocks will remain a play thing of the scientific community only.

The Atomic Clock Scientific Precision

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Precision is becoming increasingly important in modern technologies and none more so than accuracy in time keeping. From the internet to satellite navigation, precise and accurate synchronicity is vital in the modern age.

In fact many of the technologies that we take for granted in today’s world, would not be possible if it wasn’t for the most accurate machines invented – the atomic clock.

Atomic clocks are just timekeeping devices like other clocks or watches. But what stands them apart is the accuracy they can achieve. As a crude example your standard mechanical clock, such as a town centre clock tower, will drift by as much as a second a day. Electronic clocks such as digital watches or clock radios are more accurate. These types of clock drift a second in about a week.

However, when you compare the precision of an atomic clock in which a second will not be lost or gained in 100,000 years or more the accuracy of these devices is incomparable.

Atomic clocks can achieve this accuracy by the oscillators they use. Nearly all types of clock have an oscillator. In general, an oscillator is just a circuit that regularly ticks.

Mechanical clocks use pendulums and springs to provide a regular oscillation while electronic clocks have a crystal (usually quartz) that when an electric current is run through, provides an accurate rhythm.

Atomic clocks use the oscillation of atoms during different energy states. Often caesium 133 (and sometimes rubidium) is used as its hyperfine transitional oscillation is over 9 billion times a second (9,192,631,770) and this never changes. In fact, the International System of Units (SI) now officially regards a second in time as 9,192,631,770 cycles of radiation from the caesium atom.

Atomic clocks provide the basis for the world’s global timescale – UTC (Coordinated Universal Time). And computer networks all over the world stay in sync by using time signals broadcast by atomic clocks and picked up on NTP time servers (Network Time Server).

Using the WWVB Signal for Time Synchronization

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We all rely on the time to keep our days scheduled. Wristwatches, wall clocks and even the DVD player all tell us the time but on occasion, this is not accurate enough, especially when time needs to be synchronized.

There are many technologies that require extremely accurate precision between systems, from satellite navigation to many internet applications, accurate time is becoming increasingly important.

However, achieving precision is not always straight forward, especially in modern computer networks. While all computer systems have inbuilt clocks, these are not accurate time pieces but standard crystal oscillators, the same technology used in other electronic clocks.

The problem with relying on system clocks like this is that they are prone to drift and on a network consisting of hundreds or thousands of machines, if the clocks are drifting at a different rate – chaos can soon ensue. Emails are received before they are sent and time critical applications fail.

Atomic clocks are the most accurate time pieces around but these are large scale laboratory tools and are impractical (and highly expensive) to be used by computer networks.

However, physics laboratories like the North American NIST (National Institute of Standards and Time) do have atomic clocks which they broadcast time signals from. These time signals can be used by computer networks for the purpose of synchronization.

In North America, the NIST broadcasted time code is called WWVB and is transmitted out of Boulder, Colorado on long wave at 60Hz. The time code contains the year, day, hour, minute, second, and as it is a source of UTC, any leap seconds that are added to ensure parity with the rotation of the Earth.

Receiving the WWVB signal and using it to synchronize a computer network is simple to do. Radio reference network time servers can receive this broadcast throughout North America and by using the protocol NTP (Network Time Protocol).

A dedicated NTP time server that can receive the WWVB signal can synchronize hundreds and even thousands of different devices to the WWVB signal ensuring each one is to within a few milliseconds of UTC.

Atomic Clock Synchronization made easy with a NTP Time Server

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Atomic clocks are the ultimate in timekeeping devices. Their accuracy is incredible as an atomic clock will not drift by as much as a second within a million years, and when this is compared to the next best chronometers, such as electronic clock that can drift by a second in a week, an atomic clock is incredibly more precise.

Atomic clocks are used the world over and are the heart of many modern technologies making capable a multitude of applications that we take for granted. Internet trading, satellite navigation, air traffic control and international banking are all industries that rely heavily on

They also govern the world’s timescale, UTC (Coordinated Universal Time) which is kept true by a constellation of these clocks (although UTC has to be adjusted to accommodate the slowing of the Earth’s spin by adding leap seconds).

Computer networks are often required to run synchronized to UTC. This synchronisation is vital in networks that conduct time sensitive transactions or require high levels of security.

A computer network without adequate time synchronization can cause many issues including:

Loss of data

  • Difficulties in identifying and logging errors
  • Increased risk of security breaches.
  • Unable to conduct time sensitive transactions

For these reasons many computer networks have to be synchronized to a source of UTC and kept as accurate as possible. And although atomic clocks are large bulky devices kept in the confines of physics laboratories, using them as a source of time is incredibly simple.

Network Time Protocol (NTP) is a software protocol designed solely for the synchronisation of networks and computer systems and by using a dedicated NTP server the time from an atomic clock can be received by the time server and distributed around the network using NTP.

NTP servers use radio frequencies and more commonly the GPS satellite signals to receive the atomic clock timing signals which is then spread throughout the network with NTP regularly adjusting each device to ensure it is as accurate as possible.

MSF Outages for 2010

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Users of the National Physical Laboratory’s (NPL) MSF time and frequency signal are probably aware that the signal is occasionally taken off-air for scheduled maintenance.

NPL have published there scheduled maintenance for 2010 where the signal will be temporarily taken off-air. Usually the scheduled downtimes lasts for less than four hours but users need to be aware that while NPL and VT Communications, who service the antenna, make every effort to ensure the transmitter is off for a brief amount of time as possible, there can be delays.

And while NPL like to ensure all users of the MSF signal have advanced warning of possible outages, emergency repairs and other issues may lead to unscheduled outages. Any user receiving problems receiving the MSF signal should check the NPL website in case of unscheduled maintenance before contacting your time server vendor.

The dates and times of the scheduled maintenance periods for 2010 are as follows:

* 11 March 2010 from 10:00 UTC to 14:00 UTC

* 10 June 2010 from 10:00 BST to 14:00 BST (UTC + 1 hr)

* 9 September 2010 from 10:00 BST to 14:00 BST (UTC + 1 hr)

* 9 December 2010 from 10:00 UTC to 14:00 UTC

As these scheduled outages should take no longer than four hours, users of MSF referenced time servers should not notice any drop off in accuracy of their network as their shouldn’t be enough time for any device to drift.

However, for those users concerned about accuracy or require a NTP time server (Network Time Server) that doesn’t succumb to regular outages, they may wish to consider investing in a GPS time server.

GPS time servers receive the time from the orbiting navigational satellites. As these are available anywhere on the globe and the signals are never down for outages they can provide a constant accurate time signal (GPS time is not the same as UTC but is easily converted by NTP as it is exactly 17 seconds behind due to leap seconds being added to UTC and not GPS).

How to Synchronise a Computer Network using the Time Protocol (NTP)

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Synchronisation of modern computer networks is vitally important for a multitude of reasons, and thanks to the time protocol NTP (Network Time Protocol) this is relatively straightforward.

NTP is an algorithmic protocol that analyses the time on different computers and compares it to a single time reference and adjusts each clock for drift to ensure synchronisation with the time source. NTP is so capable at this task that a network synchronised using the protocol can realistically obtain millisecond accuracy.

Choosing the time source

When it comes to establishing a time reference there really is no alternative than to find a source of UTC (Coordinated Universal Time). UTC is the global timescale, used throughout the world as a single timescale by computer networks. UTC is kept accurate by a constellation of atomic clocks throughout the world.

Synchronising to UTC

The most basic method of receiving a UTC Time source is to use a stratum 2 internet time server. These are deemed stratum 2 as they distribute the time after first receiving it from a NTP server (stratum 1) that is connected to an atomic clock (stratum 0). Unfortunately this is not the most accurate method of receiving UTC because of the distance the data has to travel from host to the client .

There are also security issues involved in using an internet stratum 2 time source in that the firewall UDP port 123 has to be left open to receive the time code but this firewall opening can, and has been, exploited by malicious users.

Dedicated NTP Servers

Dedicated NTP time servers, often referred to as network time servers, are the most accurate and secure method of synchronising a computer network. They operate externally to the network so there are no firewall issues. These stratum 1 devices receive the UTC time direct from an atomic clock source by either long wave radio transmissions or the GPS network (Global Positioning System). Whilst this does require an antenna, which in the case of GPS has to be placed on a rooftop, the time server itself will automatically synchronise hundreds and indeed thousands of different devices on the network.

Five Reasons why your Network needs a NTP Server

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Accurate timekeeping if quite often overlooked as a priority for network administrators yet many are risking both security and data loss by not ensuring their networks are synchronised as precisely as possible.

Computers do have their own hardware clocks but these are often just simple electronic oscillators such as exist in digital watches and unfortunately these system clocks are prone to drift, often by as much as several seconds in a week.

Running different machines on a network that have different times – even by only a few seconds – can cause havoc as so many computer tasks rely on time. Time, in the form of timestamps, is the only reference computers use to distinguish between different events and failure to accurately synchronize a network can lead to all sorts of untold problems.

Here are some of the major reasons why your network should be synchronised using Network Time Protocol, prefasbly with a NTP time server.

Data Backups – vital to safeguard data in any business or organization, a lack of synchronisation can lead to not only back ups failing but older versions of files replacing more modern versions.

Malicious Attacks – no matter how secure a network, somebody, somewhere will eventually gain access to your network but without accurate synchronisation it may become impossible to discover what compromises have taken place and it will also give any unauthorised users extra time inside a network to wreak havoc.

Error logging – when faults occur, and they inevitably do, the system logs contain all the information to identify and correct problems. However, if the system logs are not synchronised it can sometimes be impossible to figure out what went wrong and when.

Online Trading – Buying and selling on the internet is now commonplace and in some businesses thousands of online transactions are conducted every second from seat reservation to buying of shares and a lack of accurate synchronisation can result in all sorts of errors in online trading such as items being bought or sold more than once.

Compliance and legality – Many industrial regulations systems require an auditable and accurate method of timing. A unsynchronised network will also be vulnerable to legal issues as the exact time an event is alleged to have taken place can not be proved.

Did you Remember the Leap Second this Year?

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When you counted down on New Year’s Eve to mark the beginning of the next year did you start at 10 or 11? Most revelers would have counted down from ten but they would have been premature this year as there was an extra second added to last year – the leap second.

Leap seconds are normally inserted once or twice a year (normally on New Year’s Eve and in June) to ensure the global timescale UTC (Coordinated Universal Time) coincides with the astronomical day.

Leap seconds have been used since UTC was first implemented and they are a direct result of our accuracy in timekeeping. The problem is that modern atomic clocks are far more accurate timekeeping devices than the earth itself. It was noticed when atomic clocks were first developed that the length of a day, once thought to be exactly 24 hours, varied.

The variations are caused by the Earth’s rotation which is affected by the moons gravity and tidal forces of the Earth, all of which minutely slow down the earth’s rotation.

This rotational slowing, while only minuscule, if it is not checked then the UTC day would soon drift into the astronomical night (albeit in several thousands of years).

The decision on whether a Leap Second is needed is the remit of the International Earth Rotation Service (IERS), however, Leap Seconds are not popular with everybody and they can cause potential problems when they are introduced.

UTC is used by NTP time servers (Network Time Protocol) as a time reference to synchronise computer networks and other technology and the disruption Leap seconds can cause is seen as not worth the hassle.

However, others, such as astronomers, say that failing to keep UTC in line with the astronomical day would make studying of the heavens nearly impossible.

The last leap second inserted before this one was in 2005 but there have been a total of 23 seconds added to UTC since 1972.

Rubidium Oscillators Additional Precision for NTP Serve (Part 2)

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Continued…

However, there are some occasions when a time server can lose connection with the atomic clock and not receive the time code for a prolonged period of time. Sometimes this may be because of downtime by the atomic clock controllers for maintenance or that nearby interference is blocking the transmission.

Obviously the longer the signal is down the more potential drift may occur on the network as the crystal oscillator in the NTP server is the only thing keeping time. For most applications this should never be a problem as the most prolonged period of downtime is not normally more than three or four hours and the NTP server would not have drifted by much in that time and the occurrence of this downtime is quite rare (maybe once or twice a year).

However, for some ultra precise high end applications rubidium crystal oscillators are beginning to be used as they don’t drift as much as quartz. Rubidium (often used in atomic clocks themselves instead of caesium) is far more accurate an oscillator than quartz and provides better accuracy for when there is no signal to a NTP time server allowing the network to maintain a more accurate time.

Rubidium itself is an alkali metal, similar in properties to potassium. It is very slightly radioactive although poses no risk to human health (and is often used in medicine imaging by injecting it into a patient). It has a half life of 49 billion years (the time it takes to decay by half – in comparison some of the most lethal radioactive materials have half-lives of under a second).

The only real danger posed by rubidium is that it reacts rather violently to water and can cause fire

Rubidium Oscillators Additional Precision for NTP Serve (Part 1)

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Oscillators have been essential in the development of clocks and chronology. Oscillators are just electronic circuitry that produces a repetitive electronic signal. Often crystals such as quartz are used to stabilise the frequency of the oscillation,

Oscillators are the primary technology behind electronic clocks. Digital watches and battery powered analogue clock are all controlled by an oscillating circuit usually containing a quartz crystal.

And while electronic clocks are many times more accurate than a mechanical clock, a quartz oscillator will still drift by a second or two each week.

Atomic clocks of course are far more accurate. They still, however, use oscillators, most commonly caesium or rubidium but they do so in a hyper fine state often frozen in liquid nitrogen or helium. These clocks in comparison to electronic clocks will not drift by a second in even a million years (and with the more modern atomic clocks 100 million years).

To utilise this chronological accuracy a network time server that uses NTP (Network Time Protocol) can be used to synchronise complete computer networks. NTP servers use a time signal from either GPS or long wave radio that comes direct from an atomic clock (in the case of GPS the time is generated in a clock onboard the GPS satellite).

NTP servers continually check this source of time and then adjust the devices on a network to match that time. In between polls (receiving the time source) a standard oscillator is used by the time server to keep time. Normally these oscillators are quartz but because the time server is in regular communication with the atomic clock say every minute or two, then the normal drift of a quartz oscillator is not a problem as a few minutes between polls would not lead to any measurable drift.

To be continued…