VIENNA - With the precision of a surgeon, Andreas Rupp carefully wraps sensor strips around a 21-tonne bell in Vienna's famous St Stephen's Cathedral.

Europe's second-largest bell, nicknamed "Pummerin", is one of several famous bells across the continent being checked to determine their life spans, and unlock the secret of the optimum chime.

Using acceleration sensors and echo microphones, the sensor strips are like electro-cardiograms that determine the health of human hearts, Rupp said.

"The Pummerin is well," determines Rupp, a project scientist and professor at the Polytechnic College in the German city of Kempten. "We just want to know how long it can be healthy and if there is any risk she could crack like so many others."

Hamburg's Millennium Bell has already undergone the examination, and bells in Paris's Notre Dame Cathedral and London's St Paul's Cathedral -- which British partners in the project favored over Big Ben in the Houses of Parliament -- are lined up as the next patients.

The project was triggered by a debate 10 years ago among bell-makers who wanted to determine if bell clappers were hitting the right spot.

Every time a clapper hits, it causes a slight deformation and strains the metal, mostly bronze or bronze alloys. Experts say the location and force of the clapper's hit -- as well as what it is made of -- will have an impact. The sensors record how hard the hit, how deformed the bell is, and its chime.

Dangers also lurk in modernization, they add.

Churches opting for mechanical, even computerized systems over human ringers might shorten their bells' lifespan, some say. Others think a switch from softer clappers to steel ones about 100 years ago has added to the damage.

"Many fear historic bells could be damaged severely or even destroyed by this new way of ringing," said Rupp.

"Computers chime the bells as they were programmed to do. Humans can always use their hearing, and go 'oh, that didn't sound so nice,' or 'ouch, that was much too hard'," he said.


In the past it would have taken about 10 people to chime the Pummerin, but now it happens at the flick of a switch. Since the bell has only been in action for around 50 years, it might still have plenty of bongs in it yet.

Its predecessor was cast in 1711 with metal from cannon balls used by the Turks during an unsuccessful siege of the city in 1683, but was destroyed in World War Two.

The current bell was cast from remainders of the old one and new material in 1952.

Even if the Pummerin is a youngster in bell terms Peter Grassmayr, a 14th-generation bell-founder and the Austrian partner in the project, has no doubt about its destiny.

"One day or another, every bell will crack," said Grassmayr standing next to the bell, which spans more than 3 meters and is nearly the same height. "We simply hope to extend their life span with our project."

Sparing usage can also work in a bell's favor. Many great bells -- like Big Ben in the Houses of Parliament in London -- ring daily or hourly but the Pummerin only chimes on special occasions, like high church days, the death of a pope or at midnight on New Year's Eve.

For Austrians themselves, the Pummerin is not just a bell but a symbol of their identity that marks big events throughout their lives, said the dome's priest Toni Faber.

"It is a voice of freedom, a voice of hardship, a voice of hope and a voice of a new life," he said, proudly glancing at the Pummerin. "I can hear all that when I hear the Pummerin."