Rubidium Oscillators – Additional Precision for NTP Servers
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.
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
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