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Adixen - Vacuum technology glossary
Category: General technical and industrial > Vacuum technology
Date & country: 15/11/2007, UK
Words: 27

'Adixen Turbo Hybrid� Pump, hybrid turbo-molecular pump from Alcatel adixen, with turbo and molecular stages.

Adixen Turbo Pump'', classic turbo-molecular pump from Alcatel adixen, without molecular stage.'

Back diffusion
If an oil-lubricated pump is operated on a vacuum tank for a long period without a process gas load, the pressure stabilises. Any measuring device connected will show no further pressure changes. However, this does not mean that no more gases are being pumped. Rather, a dynamic balance is set. The flow of gas pumped out of the tank is of the same magnitude as the flow of gas diffused back out of the oil-lubricated pump. In the first instance, gases which adhere to the surface, such as water vapour, are pumped out of the tank, and the gas flowing back is oil mist in the first instance. This “back diffusion� occurs primarily at high temperatures and low pressures. It can be avoided by using condensation traps, molecular sieves or a carrier gas flow.

Detection limit
The detection limit indicates the value of a measuring system, up to which a measurement (of gas) can be reliably detected with the measuring system. The reliability of the detection is defined by a statistically specified so-called confidence interval. In circumstances where the measurement values are under or over the detection limit, they are designated as immeasurable within the scope of the measurement technique. In practice, this means that it is the user who must decide for themselves, which difference or which quotients between the measured signal and the test gas background are to be determined as adequate or satisfactory in order to obtain a clearly-defined result of ‘good` or ‘bad` in the test. A very conservative value is when the measured leakage rate signal is greater than the background leakage rate by a factor of 10. Sophisticated measuring equipment or the use of zero suppression can help to obtain a reliable ‘good` or ‘bad` test result even in case of a bad signal-to-noise ratio.

Diaphragm pump
The diaphragm pump is a particular form of piston pump in which the medium to be delivered is drawn up and expelled by a diaphragm instead of a piston.

Electrons are negatively charged elementary particles, which encircle the positively charged core of an atom. Freely moving electrons can transport an electrical current.

The registered trademark “Fomblin� is synonymous now with PFPE-based special oils. This polyfluoropolyether is used as a lubricant in applications in which High resistance to chemicals and slow reaction High thermal stability No spontaneous or ignition flammability Avoidance of inflammable mixtures and oxygen compatibility are required.

Forming gas
forming gas is a collective name for less-active gas mixtures consisting of nitrogen N2 and hydrogen H2, where the ignition limit in comparison to pure hydrogen is massively reduced or completely eliminated. Forming gas is used in the working of metals at heat, for example in soldering, welding (join protection), milling, pressing and annealing. The hydrogen contained in the gas works reductively on metal oxides and prevents oxidation from occurring. Forming gases are non-toxic, but at a hydrogen composition of less than 5.5% they are non-flammable.

Wolfgang Max Paul Gaede, *1878 in Lehe; †1945 in Munich, was a German physicist and a pioneer in vacuum technology who invented a number of vacuum pumps and worked in radio and communications technology and a range of other fields.

Gaede pump
A molecular pump in which the pumping action is produced by a rotor in the form of a smooth disk. The stator is provided with spiral guide grooves. The design of the construction can also be reversed, with the stator being smooth and the rotor having the guide grooves.

At room temperature, helium is a colourless and odourless gas. After hydrogen, it is the chemical element with the lowest density and has the lowest melting point of all elements. As with all other noble gases (neon, argon, krypton, xenon) helium is very inert. Therefore there are no known helium compounds in nature. Helium (helium I) changes state at low temperatures (helium II). Helium II is the best conductor of heat known and has a heat conductivity which is 300 times higher than silver. In addition it flows without internal friction and penetrates even the tiniest of openings. Because of these properties, helium II is also referred to as a superfluid. In normal air, sound travels at a speed of around 330 metres per second, but in helium gas it travels at twice the speed. This explains the Mickey Mouse effect on the voice when helium is inhaled.

Fernand Holweck, *1890 in Paris; †1941 in Paris, was a French physicist who made important contributions in the fields of vacuum technology, electromagnetic radiation and gravitation. In the twenties, Holweck built the first prototype of a television set.

Holweck pump
A molecular pump in which the pumping action is produced by a rotor in the form of a smooth cylinder. The stator is provided with spiral guide grooves. The design of the construction can also be reversed, with the stator being smooth and the rotor having the guide grooves.

An ion is an electrically charged atom or molecule. It may comprise one or more atoms and be positively (cation) or negatively (anion) charged. The number of positively charged core modules (protons) in atoms is identical to the number of negatively charged electrons which encircle the core. An atom is outwardly electrically neutral. An ion is charged by the imbalance of positive charges in the core and negative charges in the electron shell.

Molecular Drag Pump, a molecular pump from Alcatel adixen without turbo-rotor, in which the pumping action is produced by Holweck stages.

Multistage Roots pump
A rotary positive displacement pump in which two impellers of equal cross-section rotate in opposite directions inside the pump casing, usually in a figure of eight movement, without touching each other or the casing wall. The two rotary pistons are synchronised so that they pass each other with close tolerances. No compression takes place in the suction chamber of the pump.

After hydrogen atoms, helium atoms are the second most frequently occurring atoms in the universe, with a proportion of 7.19%. While they only represent a low proportion (0.0000004%) of the earth's lithosphere, their presence in the composition of the air is 0.00046%. The noble gas is also found in larger volumes as a radioactive breakdown product in natural gas and crude oil, which can contain up to 10% helium. In the sun, the element is produced by nuclear fusion processes from hydrogen atoms. Many radioactive substances emit so-called alpha rays, consisting of doubly ionised helium nuclei which have lost their electrons. Helium atoms with mass number 4 (helium 4) have 2 protons, 2 electrons and 2 neutrons. Natural helium consists of a mixture of two different isotopes. However, with a proportion of 0.00014%, the helium 3 isotope (with only one neutron) occurs relatively rarely.

The Penning vacuum meters operate at pressure ranges between around 10-2 and 10-9 mbar. The filament-less measurement cell generates glow discharge by applying a high voltage. The electrons obtain high energy from the glow discharge. They collide with and ionise neutral gas particles. Gas particles generated in this way are accelerated through an electrical field to a collector. The resulting ion flow is a measurement of the pressure in the measurement cell.

Pirani vacuum meter
Vacuum meter frequently named after its inventor, Berlin physicist Marcello Pirani (1880-1964). It works within the pressure range from around 10-4mbar to 1000 mbar and uses the dependency of pressure on heat conductivity as an indirect measured variable for pressure. The change in heat conductivity is measured on the basis of the change in resistance of an electrically heated wire.

Piston pump
A piston pump is a machine for delivering liquids or gases, whereby gases may also be compressed. In the first part of the cycle, the medium to be pumped is drawn up through an inlet valve by a piston moving inside a cylinder. This is then discharged through an outlet valve. This process is also referred to as positive displacement pumping. Piston pumps enable high pressures to be achieved when pumping liquids. In addition, the volume of liquid delivered can be precisely determined. The pump can be driven manually, by solenoid or by motor.

A rotor is the turning (rotating) part of a machine, e.g. in a washing machine, clock, computer, helicopter or our vacuum pumps. The rotor in a rotary vane vacuum pump is a slotted cylinder in which two blades are inserted. These are pushed outwards towards the stator by springs and centrifugal force during rotation. This generates a closed space in which gases can be conveyed.

Scroll pump
A scroll pump is a vacuum pump which works on the displacement principle. It consists of two interleaved Archimedes spirals. One of these spirals is fixed, the other is driven in an eccentric orbit. Thus individual closed pockets are produced between these spirals and their volumes become smaller and smaller. In this way, the gas to be pumped is drawn in from the outside, compressed in the pump and expelled through a connection in the centre of the spiral.

Sniffing test
In a sniffing test, the test object is filled with test gas. The test gas (for example hydrogen or helium) flows out through leaks and is detected by a sniffing probe, either through manual use or using a pre-installed probe. This probe feeds into a detector. The leading types of detector are sector mass spectrometers or semiconductor sensors.

Sputtering (atomisation)
Sputtering is the bombardment of a surface with high-energy ions. The bombardment generates a pulse transfer similar to snooker balls in which individual atoms are released from a solid and enter their gaseous phase.

A stator is the stationary, non-moving part of a machine, e.g. in an electric motor, generator, hydraulic motor or pump; the opposite to the rotor, the rotating part of the machine. The stator is often part of the housing, and is made of metal in most vacuum pumps but occasionally of plastic.

Wide-range pump
Also wide-range turbo pump; the common name for the hybrid turbo-molecular pump.

Zero suppression
Using zero suppression will place a zero value on the display screen of a measuring device. This means that a real, measured background leakage rate is shown as value zero. The value of the background leakage rate can therefore be anything. Zero suppression is used in test gas leak detection most often when there is a very high concentration of the test gas in the immediate environment. A zero suppression is used with small leakage signals and a simultaneously high test gas background to obtain a reliable representation of the zero value and to increase the display resolution - so for example in Sniffing test leakage detection or in highly sensitive measuring at the detection limits of detectors.