Physikalisch-Technische Bundesanstalt (PTB)

What they do

The Physikalisch-Technische Bundesanstalt is Germany's national metrology institute and the country's highest authority for correct and reliable measurement. It employs about 2,100 people, roughly 1,700 of them in Braunschweig, with a second site in Berlin-Charlottenburg. Its legal tasks are set out in the Units and Time Act, and one of them is unusual: PTB is responsible for realising and disseminating Germany's legal time.

Why it matters

Almost everything that is measured and sold in Germany, from electricity meters to fuel pumps, traces back to standards kept at PTB. The institute also feeds its caesium clocks into the international time scale. Its best known public service is the DCF77 long-wave signal from Mainflingen near Frankfurt, which carries time and date every minute to receivers within roughly 2,000 kilometres. Deutsche Bahn station clocks, traffic light controllers, energy suppliers and millions of household radio-controlled clocks all listen to it.

Products to know

• DCF77 time signal: the long-wave broadcast that has set Europe's radio-controlled clocks since the 1970s.
• Primary caesium fountain clocks and optical clocks, which contribute to international atomic time and to research on a future redefinition of the second.

The German angle

PTB began life in Berlin in 1887 as the Physikalisch-Technische Reichsanstalt, proposed by the industrialist Werner von Siemens and the physicist Hermann von Helmholtz, who became its first president. Siemens wanted a neutral home for quality assurance and standards for the young electrical industry. The Reichsanstalt became a landmark in the history of physics: in 1900 Heinrich Rubens and Ferdinand Kurlbaum measured black-body radiation there, and their far infrared results, shared with Max Planck over dinner on 7 October 1900, helped Planck find the radiation formula that opened quantum physics. The present PTB was founded in Braunschweig in 1950.

Sources

• PTB: About us
• Adlershof: Precision made in Berlin
• Wikipedia: Heinrich Rubens