The weary battery of your clock may
halt the tick-tock temporarily but the fact remains that time never stops. As
you place a new battery, the tick-tock is once again restored but you have to
adjust the clock to the exact time. Now for adjusting your clock, you perhaps
set the time according to clocks that are in function. But what is the surety
that the time displayed by those clocks is accurate? This challenge of
non-synchronicity of the clocks in use is most evident when you miss your train
or flight by a few minutes or find your bank closed for the day, which may
sometimes cost you quite heavily.
Well, you could just dial 174 and
know the exact time of the day — the Indian Standard Time (IST) — precise to
the second! Maintained by the Time and Frequency Standards Laboratory at the National Physical Laboratory
(NPL), CSIR, the IST is followed by the Doordarshan and the All India Radio
(AIR) for the announcement of accurate time, which most of us listen to for
adjusting time in our hand watches and wall clocks. Another
increasingly popular means of obtaining the time is through Global Positioning
System (GPS) receivers.
Now comes the question of
disseminating the IST across the nation. The most common method is to transmit
the time signal via satellites or from a broadcast station. The classic example
is the transmission of the Standard Time and Frequency Signal (STFS) via INSAT
by the NPL, CSIR. INSAT satellite based
standard time and frequency broadcast
service offers IST correct up to ±10 microsecond on a continuous
basis. However, there is still a considerable variance in the display of
time by other customer service providers like the Indian Railways, Airlines,
Banks and so on. For example, the times displayed by clocks on different
platforms of a railway station are often quite different. This strongly
necessitates the need for synchronizing the clocks for display in public places
to one source clock. In the fast paced life of today, synchronization of time
has surely assumed importance.
In
a landmark achievement, CSIR has fulfilled the requirement of one and all for
easy access of IST data for updating the local clocks. The wonder product is a
‘Teleclock’, which has been developed by a team of scientists led by Dr P.
Banerjee, Head of the Time and Frequency Section at
NPL, CSIR, New Delhi. Dr Banerjee conceived the idea of developing a
Teleclock sometime in 1994-95. Today this innovative Teleclock Service is the
first of its kind in India, which is a digital time data service, facilitated
through the telephone network. Simply put, the Teleclock has a unique in-built
system, which auto-dials the telephone number of the Teleclock Service at the
user-defined time. It has its own clock and a modem that facilitates the
connection to the local telephone line.
NPL maintains
the IST with the help of a bank of caesium atomic clocks, which are so accurate
that it is only one second that they can lose or gain in a span of 30,000
years! “The
primary standard of time the world over is Cesium atomic clock. Cesium is
preferred because of its long-term, high order stability”, says Dr Banerjee. “These atomic clocks are synchronized with the
worldwide system of clocks that support the Coordinated Universal Time, through GPS
network,” he further adds.
As
the NPL numbers are dialed by the Teleclock, the internal clock gets
synchronized with the help of received time data through the telephone line.
After the time updation, the Teleclock automatically gets disengaged. An
additional feature provided in the Teleclock Service is to set the Real Time
Clock (RTC) of a computer. All that is required is that the computer should be
connected to a telephone line through a standard modem. For this, the NPL
scientists have developed the necessary software for the computer's RTC. This
cost-effective way of disseminating universal standard time for all users in
the country was launched in February 2000. Dr P. Banerjee has to his
credit a US Patent (No. 6091804, dated July 18, 2000) entitled, ‘Device
Useful as Master/Slave Clock for Transmitting Standard Time Over a Telephone
Network and a Telephone Network Incorporating the Device for Transmitting and
Receiving Standard Time.’
The
Teleclock service through the landline network is, however, accessible to users
having a landline telephone, which becomes a limiting factor for some key applications
like police patrolling vans, remote locations where telephone lines are not
available and personal vehicles. The NPL scientists have met this challenge by
adding a new dimension to time dissemination by developing an improved version
of the Teleclock.
In
a significant advancement, Dr P. Banerjee’s team has developed the
Mobile Teleclock receiver that receives data through wireless mobile telephone
network. The receiver has the
provision of dialing the telephone number of the line dedicated for this
service manually by pressing a switch or automatically at a pre programmed
time. The Mobile
Teleclock receiver was formally
launched by Prof. Samir K. Bramachari, former Director General CSIR on July 28,
2009. This improved Teleclock
receiver is an inexpensive and advanced solution to access Standard Time of any
country without any separate landline telephone connection. The basic
requirement of the Teleclock receiver for mobile network is that it should have
GSM SIM card with ‘Data Communication Mode Enabled’. For this innovation, patents have been granted in India as
well as in the United States Patent and Trademarks Office, besides five
European countries namely, Germany, France, U.K., Italy and Sweden. A patent No.1390DEL2009 on, ‘Improved
Teleclock Receiver Utilizing Mobile Telephone Network’ by P. Banerjee, P. P.
Thorat and A. K. Suri was filed in 2009 in India, Japan, Korea and Europe.
NPL has also transferred this technology to M/s Excel
Technologies, based in Noida, on a non-exclusive basis. The other manufacturers
to whom this technology has been transferred include M/s Bihar Communications
Pvt. Ltd. in Patna and M/s Electronics Equipment Company based in Kolkata. The
Mobile Teleclock is currently in use in the Parliament House, airports, railway
platforms, Delhi police control rooms, besides the CSIR laboratories and some
private organizations. But why this highly useful, scientifically developed
product still not popular with the Indian masses? To this Dr Banerjee says, “Manufacturers in our country are not so
aggressive. As there is low profit per unit, bulk orders are few”. “The need is
to give a more decorative look to the otherwise boxy appearance of the Mobile
Teleclock receiver, so that people are interested to buy it. As the demand increases,
manufacturers will have to produce more units and this will reduce the cost per
unit”, Dr Banerjee explains. This service can be implemented in any country
with very low investment like it is operational in Saudi Arabia and Nepal.
Box
Atomic Clocks
All clocks basically keep
track of the passage of time by counting the ‘ticks’ or oscillations of a ‘resonator’. The oscillation in an ordinary clock is between the balance wheel and the
hairspring, while the oscillation in an atomic clock is between the nucleus of
an atom and the surrounding
electrons. Similarly, in a pendulum clock the resonator is a pendulum, which swings back
and forth. The gears in the clock keep track of time by counting the
resonations of the pendulum, which are usually at a frequency of one swing per
second. A digital clock uses
either the oscillations on the power line or the oscillations of a quartz
crystal as the resonator, and counts them
using digital counters. Needless to say, the accuracy of the clock is dependent
on the accuracy of the resonator at the specified frequency.
Atomic clocks are the most accurate keepers of time. They are, however, not radioactive as they do not rely on atomic
decay. They use the resonance frequencies of atoms as its resonator.
Cesium-133 oscillates at 9,192,631,770 cycles per second.
The oscillation frequencies within the atom are determined by the mass and the
gravity and electrostatic ‘spring’ between the positive charge on the nucleus
and the electron cloud surrounding it. Atoms of different elements have their
characteristic oscillation frequencies.
The accuracy of an atomic clock is completely
different from the accuracy of a quartz
clock. In a quartz clock, the quartz
crystal is manufactured so that its oscillating frequency is close to some
standard frequency, but every crystal may be slightly different, and
temperature could change its frequency. Whereas a cesium atom always resonates at
the same known frequency, which makes an atomic clock so precise.
There are different types of atomic clocks,
which only differ with regard to the element used and the means of detecting
the changes in the energy level. The various types of atomic clocks are: Cesium atomic clocks that employ a beam of cesium atoms; Hydrogen
atomic clocks that use hydrogen atoms at the required energy level and Rubidium
atomic clocks that use rubidium gas. The most accurate atomic
clocks use the cesium atom (Cesium 133).
The
genesis for developing an atomic clock took root in 1945, which was based on
the technique called atomic beam magnetic resonance developed by Isidor
Rabi, a physics professor of the Columbia University. In 1949, the National
Bureau of Standards (now the National Institute of Standards and Technology,
NIST) announced the world’s first atomic clock using the ammonia molecule. Later in 1952 it came up with the first
atomic clock using cesium atoms as the source of vibrations. The National
Physical Laboratory in England built the first cesium-beam clock in 1955 that
was used as a calibration source.
The keeper of Indian Standard Time (IST), NPL, CSIR has
five such atomic clocks. A cesium atomic clock typically has a life span of
less than a decade. They are electronic boxes with digital displays, stacked
together in a sanitized chamber at an appropriate temperature and humidity. Atomic clocks make GPS
navigation possible, and help synchronizing the Internet.
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