Projects: Time Signal

One of the world’s most accurate time signals comes from Braunschweig. It is transmitted together with a weather report from Mainflingen to almost everywhere in Europe.

The statutory time for the Federal Republic of Germany comes from the Physikalisch-Technische Bundesanstalt (PTB) metrology institute in Braunschweig. Its atomic clocks are some of the most accurate in the world. They gain or lose just one second every two million years. Approximately 100 million radio clocks rely on this time signal, which is transmitted by T-Systems from Mainflingen on the long-wave frequency 77.5 KHz via the DCF 77 transmitter.

The transmitter station houses atomic clocks that are controlled from Braunschweig. The date, day and time are broadcast as digital telegrams in addition to the ultra-precise time signal. As a result, users from almost all over Europe within a radius of 2,000 kilometers can set the correct time on their own clocks. “We guarantee a reliability level of 99.7 percent, and year after year we exceed that level many times over,” said Robert Schlicht, who is responsible for DCF 77 contract issues at T-Systems.

Here is the weather forecast

The transmitter has also been broadcasting weather reports and forecasts for 90 regions in Europe since September 2006. At the same time, the Mete-On 1 was launched on the market – the first clock to display not only the time, but also the weather for the current day and the following three days. “A wristwatch will be available in the summer,” said Reiner Häcker from HKW. The company HKW in Seebach, Thuringia, developed the entire weather-data transmission system and the necessary receiver modules, as well as the hardware and software. In future, it is planned to upgrade the program with a disaster warning function. They will replace the largely dismantled siren network with a silent alarm. Successful experiments have already been completed. The integration of receivers in smoke detectors is also under discussion. In this way, classic and extremely reliable transmission technology is creating new markets. And an increase in safety.

Even more precise

Meanwhile, in Braunschweig the physicists are working on the designs of even more accurate clocks. The so-called caesium fountain represents one step along this path. Since 1999, a version built by the PTB has achieved a level of accuracy of one second in every 10 million years. Experts believe that optical clocks will have an excellent chance of providing even greater accuracy. This could even improve the time measurement by three powers of ten, to 10^-18. “That corresponds to a movement deviation of one second in 10 billion years, the age of the universe,” said Dr. Ekkehard Peik from the PTB. With a clock like that, it could be possible to measure the Earth’s gravity so precisely that rises and depressions in the surface could be measured in the centimeter range – for instance, if a rain low presses on the Earth and causes a scarcely perceptible depression.

However, regardless of how accurately the clocks in the laboratories may tick, the standard for everyday use in radio-controlled wristwatches and station clocks will still be the time signal of DCF 77 for many years to come.

Read the full story in the printed edition.