The
History of Pressure Measurement
1594 Galileo Galilei, born
in Pisa (Italy), obtains the patent for a machine to pump water
from a river for the irrigation of land. The heart of the pump
was a syringe. Galileo Galilei found that 10 meters was the limit
to which the water would rise in the suction pump, but had no
explanation for this
phenomenon. Scientists were then devoted to find the cause for
this.
1644 Evangelista Torricelli
(rorr). Italian physicist, filled a tube 1 meter long, hermetically
closed at one end, with mercury and set it vertically with the
open end in a basin of mercury. The column of mercury invariably
fell to about 760 mm, leaving an empty space above its level.
Torricelli attributed the cause of the phenomenon to a force
on the surface of the earth, without knowing, where it came from.
He also concluded that the space on top of the tube is empty,
that nothing is in there and called it a "vacuum".
1648 Blaise Pascal, French
philosophei physicist and mathematician, heard about the experiments
of Torricelli and was searching for the reasons of Galileo's
and Torricelli's findings. He came to the conviction that the
force, which keeps the column at 760 mm, is the weight of the
air above.
Thus, on a mountain, the force must be reduced by the weight
of the air between the valley and the mountain. He predicted
that the height of the column would decrease which he proved
with his
experiments at the mountain Puy de Dome in central France. From
the decrease he could calculate the weight of the air. Pascal
also formulated that this force, he called it "pressure",
is acting uniformly
in all directions.
1656 Offo von Guericke,
born in Magdeburg/Germany. Torricellis conclusion of an empty
space or "nothingness" was contrary to the doctrine
of an omnipresent God and was thus attacked by the church. Guericke
developed new air pumps to evacuate larger volumes and staged
a dramatic experiment in Magdeburg by pumping the air out of
two metal hemispheres which had been fitted together with nothing
more than grease. 8 horses at each hemisphere were not strong
enough to separate them.
1661 Robert Boyle. an Anglo-Irish
chemist, used "J"-shaped tubes closed at one end to
study the relationship between the pressure and volume of trapped
gas and stated the law of x V = K (P: Pressure, V: Volume, K:
Constant) which means that if the volume of a gas at a given
pressure is
known, the pressure can be calculated if the volume is changed,
provided that neither the temperature nor the amount of gas is
changed.
1820 Almost 200 years later,
Joseph Louis Gay-Lussac. French physicist and chemist, detects
that the pressure increase of a trapped gas at constant volume
is proportional to the temperature. 20 years later, William Thomson
(Lord Kelvin) defines the absolute temperature
Mechanical
Measurement Technologies
1843 Lucien Vidie, French scientist, invented
and built the aneroid barometer, which uses a spring balance
instead of a liquid to measure atmospheric pressure. The spring
extension under pressure is mechanically amplified on an indicator
system. Employing the indicator method of Vidie, Eugene Bourdon
(founder of the Bourdon Sedeme Company) patented 1849 the Bourdon
tube pressure gauge for higher pressures.
Electrical
Measurement Technologies
1930 The first pressure
transducers were transduction mechanisms where the movements
of diaphragms, springs or Bourdon tubes are part of an electrical
quantity. Pressure diaphragms are part of a capacitance. the
indicator movement is the tap of a potentiometer.
1938 The bonded strain
gauges were independently developed by E. E. Simmons of the California
Institute of Technology and AC. Ruge of Massachuseffs Institute
of Technology. Simmons was faster to apply for a patent.
1955 The first foil strain
gauges came up with an integrated full resistor bridge, which,
if bonded on a diaphragm. see opposite stress in the center and
at the edge.
1965 The bonding connection
of the gauges to the diaphragm was always the cause for hysteresis
and instability. In the 1960's, Statham introduced the first
thin-film transducers with good stability and low hysteresis.
Today, the technology is a major player on the market for high
pressure.
1973 William R. Poyle applied
for a patent for capacitive transducers on glass or quartz basis,
Bob Bell of Kavlico on ceramic basis a few years later in 1979.
This technology filled the gap for lower pressure ranges (for
which thin film was not suited) and is today, also with resistors
on
ceramic diaphragms, the widest spread technology for non-benign
media.
The Sensor
Age
1967 Honeywell Research
Center, Minneapolis/USA, 1967: Art R. Zias and John Egan applied
for patent for the edge-constrained silicon diaphragm. 1969.
Hans W. Keller applied for patent for the batch-fabricated silicon
sensor. The technology is profiting from the enormous progresses
of IC-technology.
A modern sensor
typically weighs 0.01 grams. If all non-cristalline diaphragms
have inherent hysteresis, the precision limit of this item is
not detectable by todays means.
2000 The piezoresistive
technology is the most universal one. It applies for pressure
ranges from 100 mbar to 1500 bar in the absolute, gauge and differential
pressure mode. The slow spread of the technology in
high volume applications for non-benign media resulted from the
inability of US-companies to develop a decent housing. In 30
years, KELLER has perfected it at costs comparable to any other
technology.
For more information,
please contact... KELLER at www.keller-druck.com
