| Oscillators have been essential in the development | | | | measurable drift. |
| of clocks and chronology. Oscillators are just | | | | However, there are some occasions when a time |
| electronic circuitry that produces a repetitive | | | | server can lose connection with the atomic clock |
| electronic signal. Often crystals such as quartz are | | | | and not receive the time code for a prolonged |
| used to stabilise the frequency of the oscillation. | | | | period of time. Sometimes this may be because |
| Oscillators are the primary technology behind | | | | of downtime by the atomic clock controllers for |
| electronic clocks. Digital watches and battery | | | | maintenance or that nearby interference is |
| powered analogue clock are all controlled by an | | | | blocking the transmission. |
| oscillating circuit usually containing a quartz crystal. | | | | Obviously the longer the signal is down the more |
| And while electronic clocks are many times more | | | | potential drift may occur on the network as the |
| accurate than a mechanical clock, a quartz | | | | crystal oscillator in the NTP server is the only |
| oscillator will still drift by a second or two each | | | | thing keeping time. For most applications this |
| week. | | | | should never be a problem as the most prolonged |
| Atomic clocks of course are far more accurate. | | | | period of downtime is not normally more than |
| They still, however, use oscillators, most | | | | three or four hours and the NTP server would |
| commonly caesium or rubidium but they do so in | | | | not have drifted by much in that time and the |
| a hyper fine state often frozen in liquid nitrogen | | | | occurrence of this downtime is quite rare (maybe |
| or helium. These clocks in comparison to electronic | | | | once or twice a year). |
| clocks will not drift by a second in even a million | | | | However, for some ultra precise high end |
| years (and with the more modern atomic clocks | | | | applications rubidium crystal oscillators are |
| 100 million years). | | | | beginning to be used as they don't drift as much |
| To utilise this chronological accuracy a network | | | | as quartz. Rubidium (often used in atomic clocks |
| time server that uses NTP (Network Time | | | | themselves instead of caesium) is far more |
| Protocol) can be used to synchronise complete | | | | accurate an oscillator than quartz and provides |
| computer networks. NTP servers use a time | | | | better accuracy for when there is no signal to a |
| signal from either GPS or long wave radio that | | | | NTP time server allowing the network to maintain |
| comes direct from an atomic clock (in the case | | | | a more accurate time. |
| of GPS the time is generated in a clock onboard | | | | Rubidium itself is an alkali metal, similar in |
| the GPS satellite). | | | | properties to potassium. It is very slightly |
| NTP servers continually check this source of time | | | | radioactive although poses no risk to human health |
| and then adjust the devices on a network to | | | | (and is often used in medicine imaging by injecting |
| match that time. In between polls (receiving the | | | | it into a patient). It has a half life of 49 billion |
| time source) a standard oscillator is used by the | | | | years (the time it takes to decay by half - in |
| time server to keep time. Normally these | | | | comparison some of the most lethal radioactive |
| oscillators are quartz but because the time server | | | | materials have half-lives of under a second). |
| is in regular communication with the atomic clock | | | | The only real danger posed by rubidium is that it |
| say every minute or two, then the normal drift | | | | reacts rather violently to water and can cause |
| of a quartz oscillator is not a problem as a few | | | | fire. |
| minutes between polls would not lead to any | | | | |