Understanding How Atomic Clocks Work: Uncovering the Science Behind Timekeeping

In summary, atomic clocks use a radio receiver to pick up time signals from a precise clock, such as a Rubidium or Cesium clock, transmitted from a site in Boulder, Colorado. This radio receiver works on a low frequency and is used in other countries as well. The time signal is then synchronized to the UTC, the world time, which is administered by BIPM in Paris. While Rubidium clocks are cheaper, they have longer-term drift, making Cesium clocks a better option. However, by combining the two, a more accurate reference can be achieved. The accuracy of the time signal can be affected by propagation delay, which can be corrected through various methods. For more accurate timekeeping, a GPS locked receiver is
  • #1
biferi
191
0
I just got an Atomic Clock and googled how they work.

It says it picks up the Atoms in the Air and sets the Clock from finding out the Energy they emit or something like this.

Can you tell me what I am missing or how they work?
 
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  • #2
If you are in the U.S., there is a radio transmitter in Boulder Colorado which sends time information from an accurate clock (using a Rhubidium or Cesium standard) and this is picked up by the radio receiver in a clock or watch.

This radio receiver works on a low frequency of about 60 KHz. Some other countries have similar services. Japan had two until the Fukishima disaster destroyed one of them.
 
  • #3
It's Rubidium, Rb, atomic number 37.
 
  • #4
Yes, Rubidium should not have a "H" in it.

I checked and it is a Cesium clock used as a standard in Boulder. These are better than Rubidium.
 
  • #5
Hi biferi,

Your 'atomic clock is built around a radio receiver, as noted earlier by vk6kro.
The radio is tuned to the time signals sent by the NIST from their Ft Collins radio site WWV.
If you check the site, they even have a list of the various receivers used, probably including yours, here:
http://www.nist.gov/pml/div688/grp40/receiverlist.cfm

The atomic part of this time keeping comes from the core instrument that provides the time. An introduction to this technology, which has many interesting wrinkles, is here:
http://en.wikipedia.org/wiki/Atomic_clock

Do note that your clock will be way off, by atomic clock standards, simply because the radio signal will be several milliseconds late in arriving at your site ;) .
 
  • #6
Propagation delay is a problem for radio transmission of a time standard although a low transmitting frequency ensures negligible multi-path propagation.

So, you could add a constant correction to the indicated time to get the real time, if it mattered.

A domestic clock showing seconds would hardly notice a few millisecond error, while a seismology lab would need to do the correction.

The transmitting frequency is very accurate and unaffected by propagation so an alternative very accurate clock could be derived from just the carrier.
 
  • #7
vk6kro said:
Yes, Rubidium should not have a "H" in it.

I checked and it is a Cesium clock used as a standard in Boulder. These are better than Rubidium.

It is actually an ensemble of hydrogen masers (I think they have something like 11 of them), that is then synchronized to their cesium fountains. The reason you need both is that Cs clocks do not generate a continuous signal, it is more of a "pulsed operation". Hence, the actual time signal comes from masers which are "freewheeling"; steered by the signal from the Cs clock to avoid drift over longer timescales.

The time generated at NIST is also synchronized to the UTC, which is the "world time" (ensentially an "average" of all the Cs fountains in the world) which is administated by BIPM in Paris.

Rubidium is a reasonably good frequency standard (but about 2 orders of magnitude worse than a maser), but they are not very good clocks because of long-term drift (but they are cheap).
 
  • #8
If Boulder Colorado Transmits the Time and my Clock is picking it up.

Then why is the Time right?

I am in PA, not Boulder Colorado.
 
  • #9
biferi said:
If Boulder Colorado Transmits the Time and my Clock is picking it up.

Then why is the Time right?

I am in PA, not Boulder Colorado.

It is only approximately right. It takes about 10 millisecond for the radio signal to travel from Boulder to you.
This is of no consequence for an ordinary clock, but there are plenty of applications where this is not accurate enough; in which case you need to start using various tricks to improve the accuracy.
Time transfer is quite literally a science in its own right.
 
  • #10
biferi said:
If Boulder Colorado Transmits the Time and my Clock is picking it up.

Then why is the Time right?

I am in PA, not Boulder Colorado.
Could you tell us what the make and model of your clock is?
 
  • #11
The time signal is meant to hold your clock to within a second or so, which is more than accurate enough if the display is in seconds.

The one hour time difference between you and the transmitter is taken care of in the clock.

When you set it up, it asked you where you are or how many hours behind UTC (London England) time you are.
It then corrects the "hours" reading of the clock to allow for your location, and also for daylight saving if it applies in your location.
 
  • #12
A cesium clock has higher short term phase noise but drifts less than a rubidium clock. Using the two together results in a better reference than either.

vk6kro said:
The transmitting frequency is very accurate and unaffected by propagation so an alternative very accurate clock could be derived from just the carrier.
Not quite true. The propagation path changes as the ionosphere changes. Multipath signals can cause phase reversals.

As ionospheric ionisation changes, the virtual point of reflection rises and falls during the night and day. It is the rate of change of path length that determines the apparent frequency of the Boulder Colorado reference signals. You can estimate the ionospheric conditions from the beat frequency.

If you need an accurate clock then you should consider a GPS locked receiver. It knows where you are and so corrects for path length. However, it is still slightly effected by variation in ionospheric transit time.
 

FAQ: Understanding How Atomic Clocks Work: Uncovering the Science Behind Timekeeping

1. How do atomic clocks keep such accurate time?

Atomic clocks use the natural oscillations of atoms to measure time. These oscillations are incredibly consistent, making atomic clocks the most accurate timekeeping devices available.

2. What type of atoms are used in atomic clocks?

The most common type of atom used in atomic clocks is cesium-133. This atom has a specific frequency at which it oscillates, making it ideal for timekeeping.

3. How does an atomic clock differ from a traditional clock?

A traditional clock uses the motion of gears and hands to keep time, while an atomic clock uses the oscillations of atoms. This makes atomic clocks much more accurate and precise.

4. Can atomic clocks be affected by external factors?

Yes, atomic clocks can be affected by external factors such as temperature and magnetic fields. However, they are designed to minimize these influences and maintain their accuracy.

5. How are atomic clocks used in everyday life?

Atomic clocks are used in various technologies, such as GPS systems and telecommunications, to ensure accurate timekeeping. They are also used as a standard for international timekeeping and in scientific research.

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