The
Human Experience in Time
The human attempt to define and calibrate time through calendars and clocks has
been a millennia-long struggle. Although many of the discoveries in timekeeping
are relatively recent, the measurement of time is an ancient science. Primex
Wireless represents the last link in this long chain of innovations with its
cutting-edge and pioneering timekeeping products. Primex Wireless was the first
to introduce GPS wireless battery-operated analog clocks and first to produce a
unique battery pack with a lifespan longer than five years. The debut of our
atomic clock, a radio-controlled mechanism operating on AM signals and the
invention of the world’s first GPS-controlled wireless clock system by our
engineers using FM radio frequencies transformed the way people think about
time. Our atomic clocks receive signals from one of the government's atomic
clocks located in Boulder, Colorado, which are accurate within a thousandth of
a second and then send out the time via an AM radio signal. Though well suited
for many facilities, these atomic clocks had their limitations, as they could
not work in buildings where radio signals could not penetrate. After five years
of research and development, in 2001 Primex Wireless managed to overcome the
obstacles posed by radio-resistant buildings and created a truly accurate and
synchronized clock system that would work perfectly anywhere and everywhere:
the world’s first GPS-controlled wireless clock system! The use of an FM radio
signal to connect with U.S government’s GPS satellites, which transmit
cesium-based official time, enables an easy penetration through walls.
It is our commitment to technological innovation and our experience of over 30
years that enables us at Primex Wireless to create groundbreaking products and
to endorse them with absolute confidence. Primex Wireless has truly become the
latest link in timekeeping technology. Now, let us also point out significant
preceding links in the chain of timepieces from the ancient sundials to the
atomic clocks of our day.
Age-Old Timekeeping Devices
Probably around five or six thousand years ago ancient civilizations began
devising instruments that would tell the time of day. Many believe the
Sumerians to be the first culture to develop a timepiece. Ancient Egyptians
were apparently the next group of people dividing the day into parts comparable
to hours. Built as early as 3500 BC, obelisks – slender, tall, quadrilateral
monuments – were the precursors to sundials and their moving shadows could
partition the day into morning and afternoon. Around 1500 BC, the more accurate
and portable "shadow clock", the
sundial, came into use. This
device divided a day into 10 parts plus two "twilight hours" in the morning and
evening. Sundials remained in use for almost three thousand years and in the
quest for accuracy their shapes evolved from flat horizontal or vertical plates
to more elaborate forms. The Egyptians improved upon the sundial around 600 BC
with a
merkhet, the oldest known astronomical tool. A pair of
merkhets was used to establish a north-south meridian by aligning them with the
Pole Star. This allowed for the measurement of nighttime hours by marking the
crossing of certain stars on the sundial’s meridian. By 30 BC, 13 different
types of sundials were in use across Greece, Asia Minor and Italy.
Water clocks were among the first timekeeping devices that did not depend on
the observation of celestial objects and were used by Greeks around 400 BC.
Named
clepsydras – "water thief" in Greek – they measured the
outflow of water from a vessel to indicate time. In due course, Greek and Roman
horologists developed more elaborate and mechanized water clocks between 100 BC
and 500 AD. The Far East also contributed considerably to the enhancement of
clepsydras from the 3rd century onward.
Mechanical Clocks
The very first
mechanical clocks were developed during the
second half of the 13th century, probably by central European monks. These
early medieval clocks had no dials or arms and were massive devices made of
heavy iron frames and gears. They were usually placed in the church tower and
only struck bells on the hour by making use of the existing church bell.
Eventually, an hour hand was added to the mechanical clocks and further
enhancements enabled them to strike even the quarter-hour. By the first half of
the 15th century, small domestic clocks started to appear. Another advance was
the invention of spring-powered clocks at the beginning of the 16th century by
Peter Henlein of Nurnberg and after the 1630s, a weight-driven timepiece,
called the lantern clock, became popular in the homes of the upper classes.
Pendulum Clocks
The concept for the breakthrough in mechanical clock making is credited to
Galileo Galilei (1564-1642), who discovered in 1582 that a pendulum could be
used to keep time. Capitalizing on this discovery, in 1656 the Dutch scientist
Christiaan Huygens (1629-93) developed the first
pendulum clock,
which became the prototype for the grandfather clock. The first pendulum
clocks, referred to as "wags-on-the-wall" at that time, had short pendulums and
were hung on a wall with dangling cast-iron components that were encased in
wood before long. Huygens’ invention allowed clocks to run accurately to the
point of three minutes loss or gain per day. William Clements’s new "anchor" or
"recoil" escapement in 1671, George Graham’s compensation for temperature
variations in 1721 and John Harrison’s refinements increased the pendulum
clock’s accuracy to 1 second per day. Further advancements during the 18th and
19th centuries led to Siegmund Riefler’s clock with a nearly free pendulum in
1889. His timepiece attained an accuracy of a hundredth of a second a day and
became the standard in many astronomical observations. With R.J. Rudd’s
introduction of a true free-pendulum principle in 1898 and W.H. Shortt’s
improvement on it in 1921, the pendulum clock’s accuracy reached its peak.
Quartz Clocks
The high performance of the Shortt clock was overtaken by
quartz clocks
developed in the late 1920s and onward. The first quartz clock built by W.A.
Marrison in 1928 was accurate to within 1-2 thousandths of a second per day.
The running of a quartz clock is based on the electric property of quartz
crystals: they vibrate at an ultrasonic frequency when exposed to an electric
field, a phenomenon known as the piezoelectric effect. The vibrations of the
crystals are constant and generate virtually frictionless beats, which can be
used to measure time once delivered to the counting mechanism of a clock and
shown on an electronic display. Thanks to their increased accuracy and relative
inexpensiveness, quartz clocks soon became the dominant technology in
timekeeping. However, they had their limitations, too. They still relied on a
mechanical vibration, the frequency of which critically depended on the
crystal’s size, shape and temperature. As each quartz crystal is unique no two
crystals could generate just the same frequency.
Atomic Clocks
The timekeeping performance of quartz clocks has been substantially surpassed
by
atomic clocks. Scientists had long realized that atoms have
resonances, which are inherently stable over time and space. Thus, atoms
constituted a potential "pendulum" with a reproducible rate that could form the
basis for more accurate clocks. With the development of radar and extremely
high frequency radio communications in the 1930s and 1940s, the generation of
certain kind of electromagnetic waves (microwaves) needed to interact with
atoms became possible. In 1945, physicist Isador Rabi suggested making a clock
based on the study of atoms by using a method called atomic-beam magnetic
resonance. In 1949, the National Bureau of Standards (now the National
Institute of Standards and Technology, or NIST) built the first atomic clock
using the ammonia molecule as the source of vibrations. However, the attention
soon shifted to and remained on more promising atomic-beam devices based on
cesium. In 1952, NIST announced the first atomic clock using cesium atoms as
the vibration source and named it NBS-1. In 1967, the 13th General Conference
on Weights and Measures formally defined a second as 9,192,631,770 oscillations
or cycles of the cesium atom’s resonant frequency and the world’s timekeeping
system was divorced from its astronomical basis. After moving to its new
laboratories in Boulder, Colorado in 1952, NIST built 7 more cesium clocks:
NBS-2 in 1960, NBS-3 in 1963, NBS-4 in 1968, NBS-5 in 1972, NBS-6 in 1975.
NIST-7 had been the primary atomic time standard for the United States since it
came on line in 1993. It was 20 times more accurate than the atomic clock it
replaced and its staggering precision worked out to an error of about a
billionth of a second per day. To put it another way, this clock will stay
within one second of true time for 6 million years. Finally, NIST F1 began
operation in 1999 and with accuracy to about one second in 20 million years,
making it the most accurate clock ever made (a distinction shared with a
similar standard in Paris). As of January 2002, it was capable of keeping time
to about 30 billionths of a second per year, i.e. it would neither gain nor
lose a second in more than 30 million years. NIST F-1 is also referred to as a
fountain clock because unlike its predecessors it uses a fountain-like movement
of cesium atoms to obtain its improved reckoning of time.
Back to Top