Page 11 - trends in automation

How do you ensure that the clocks all over the world are
correct?
Ullrich: As I mentioned earlier, we have what we call Coordi­
nated Universal Time, which is valid for 24 time zones and is
­determined by around 400 atomic clocks worldwide. The clocks
are compared with one another and a mean value is created.
Less accurate clocks have a lower weighting than more accu-
rate clocks. This value is then checked to establish if it matches
the best clocks in the world, including our atomic clocks at
the PTB. The values determined in this process are released
as Coordinated Universal Time by the International Bureau of
Weights and Measures (BIPM), which has been based in
Sèvres, near ­Paris, since 1875. This happens once a month. It is
also im­portant that all atomic clocks take altitude into account
because, according to Einstein, time is influenced by the
­gravitational field.
How long is the current definition of time likely to be valid?
Ullrich: Certainly for a few more years, though the next genera-
tion of clocks is already in sight. These so-called optical clocks
are likely to be at least several hundred times more accurate
than the best atomic clocks available today. They operate
­according to a similar principle. However, the radiation that we
use here to excite the electrons has an oscillation frequency
100,000 times higher and is in the visible range. Instead of
­microwave radiation, optical clocks run with light from high-
precision lasers.
At the PTB we already have two different optical clocks, both
of which are around ten times more accurate than our atomic
clocks. Over the coming years, however, we will have to
compare and observe different optical clocks around the
world to determine whether they all tick the same and with
what kind of inaccuracy. This will take at least as long as it
takes for the definition of a second to be adapted to the new
technical possibilities.
Which role does collaboration with international partners
play in such new developments?
Ullrich: Since the signing of the Metre Convention in 1875, ­
we metrologists work together very closely and constructively,
which I think is excellent. Of course, there is also competition.
At the end of the day, everyone wants to have the best clock. In
this regard, we have been very successful. Our fountain atomic
clocks are among the most accurate in the world. In the area of
optical clocks, we are currently involved in a friendly head-to-
head race with our partner, the National Institute of Standard
and Technology (NIST) in the USA.
Professionally, you work very intensively on this topic. Does
your job influence your own personal relationship with time?
Ullrich: I think time is an extremely valuable asset. I therefore
try to use it wisely. For example, I complete various tasks that
require intensive concentration in blocks if possible. When
that is the case I don’t like to be disturbed, because you work
­extremely inefficiently if you have to keep starting over again. ­
I generally tend to work like that early in the morning or at
weekends, and tend to use my mobile phone and the Internet
very little.
The most difficult thing is getting the balance right between ­
time spent working and time with my family. This is partly due to
the fact that I love my job and often don’t even see it as work.
I sometimes forget the time.
“If our new optical clocks were as old
as the universe, they would be inaccurate
by less than ten seconds.”
Joachim H. Ullrich, Physikalisch-Technische Bundesanstalt Braunschweig, Germany
2.2013 trends in automation
Inspiration 10 – 11