A Knudsen absolute manometer is an instrument to measure absolute
pressure
Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country a ...
s. Named after
Martin Knudsen
Martin Hans Christian Knudsen (February 15, 1871 in Hasmark on Funen – May 27, 1949 in Copenhagen) was a Danish physicist who taught and conducted research at the Technical University of Denmark.
He is primarily known for his study of molec ...
.
Working principle
Pressure is determined by the interaction of particles with a surface, its
kinetic energy
In physics, the kinetic energy of an object is the energy that it possesses due to its motion.
It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its a ...
, and is
temperature
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer.
Thermometers are calibrated in various temperature scales that historically have relied on ...
dependent. When a particle hits a hotter surface, heat transfer will take place and the particle will gain energy. When a particle hits a colder surface, the opposite occurs. Particles that interact with a hotter or colder surface will exert a force on that surface. A Knudsen manometer uses this temperature-effect to make a plate with dual temperatures rotate. It consists of a rotating plate, of which the centre of rotation is in the centre of the plate. Image the plate rotating, the parts that push the 'air' are the plate parts that are 'normal' temperature, the other sides are heated. At the heated sides the particles that interact will gain kinetic energy and push to plate to rotation. By reading the speed of this rotation the pressure can be determined. (This is an interpretation from the information about Knudsen manometer from the Dutch book ''Vacuum Technologie''
)
References
Pressure gauges
Laboratory equipment
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