Vacuum gauges mechanical

Mechanical vacuum gauges measure the pressure directly by recording the force which the particles (molecules and atoms) in a gas-filled space exert on a surface by virtue of their thermal velocity. 

Nowadays a shortened McLeod type compression vacuum gauge according to Kammerer is used to measure the partial final pressure of mechanically compressing pumps. Through the high degree of... 

Figure 18.1 Diagram of the glass vacuum line showing the major components mechanical pumps, diffusion pump, vacuum gauge, main vacuum manifold, and purge valve.

Thermal Conductivity Vacuum Gauges. A very widely applied gauge of this type is the Pirani gauge. Such gauges consist of a wire (Pt, W or Ni, d = 5-20 pm / 5 cm) mounted axially in a cylindrical tube (d 2 cm). The wire is heated by an electric current to approximately 100°C above the ambient temperature and heat loss occurs by three mechanisms, as indicated in Figure 5.3. 

There are two basic ways for a vacuum gauge to read a vacuum direct and indirect. For example, say that on one side of a wall you have a known pressure, and on the other side of the wall you have an unknown pressure. If you know that a certain amount of deflection implies a specific level of vacuum, and you can measure the current wall deflection, you can then determine the pressure directly. This process is used with mechanical or liquid types of vacuum gauges. On the other hand, if you know that a given gas will display certain physical characteristics due to external stimuli at various pressures, and you have the equipment to record and interpret those characteristics, you can infer the pressure from these indirect measurements. This indirect method is how thermocouple and ion gauges operate. 

They are subject to the effects of hysteresis, or, rather, the tendency of materials to remember distortions and not return to their original shapes (mechanical gauges with glass distortion membranes will not have symptoms of hysteresis). Hysteresis of vacuum gauges can be diagnosed by the following symptoms ... 

This procedure should always be done when running any vacuum system without the use of traps because of the damage some condensable vapors can do to vacuum gauges. f On a regular vacuum system, this can be done by either (a) separating the diffusion pump from the rest of the system by stopcocks or valves or (b) the use of a nitrogen cold-trap between the mechanical and diffusion pump. 

Diaphragm vacuum gauges where the deflection of the diaphragm is not detected mechanically but by strain gauges are called electromechanical transducers. In a strain gauge a thin element (wire or foil) is stressed by tension or pressure. 

If the pump is a filter pump off a high-pressure water supply, its performance will be limited by the temperature of the water because the vapour pressure of water at 10°, 15°, 20° and 25° is 9.2, 12.8, 17.5 and 23.8 mm Hg respectively. The pressure can be measured with an ordinary manometer. For vacuums in the range lO" mm Hg to 10 mm Hg, rotary mechanical pumps (oil pumps) are used and the pressure can be measured with a Vacustat McLeod type gauge. If still higher vacuums are required, for example for high vacuum sublimations, a mercury diffusion pump is suitable. Such a pump can provide a vacuum up to 10" mm Hg. For better efficiencies, the pump can be backed up by a mechanical pump. In all cases, the mercury pump is connected to the distillation apparatus through several traps to remove mercury vapours. These traps may operate by chemical action, for example the use of sodium hydroxide pellets to react with acids, or by condensation, in which case empty tubes cooled in solid carbon dioxide-ethanol or liquid nitrogen (contained in wide-mouthed Dewar flasks) are used. 

Pressure loss coefficient, 13 261 Pressure measurement, 11 783 20 644-665. See also Vacuum measurement electronic sensors, 20 651-657 mechanical gauges, 20 646-651 smart pressure transmitters, 20 663-665 terms related to, 20 644-646 Pressure measurement devices. See also Pressure meters Pressure sensors location of, 20 682 types of, 20 681-682 Pressure meters, 20 651 Pressure microfiltration/ultrafiltration,... 

The spiral gauge consists of a hollow spiral of very thin glass or quartz fixed at the end at which it is connected to the vacuum line, the other end being closed. Changes in the difference between inside and outside pressure lead to expansion or contraction of the spiral. The resulting movement can be magnified by a mechanical or optical lever. 

The second Higgs field acts in such a way that if the vacuum expectation value is zero, ( ) = 0, then the symmetry breaking mechanism effectively collapses to the Higgs mechanism of the standard SU(2) x U(l) electroweak theory. The result is a vector electromagnetic gauge theory 0(3)/> and a broken chiral SU(2) weak interaction theory. The mass of the vector boson sector is in the A(3) boson plus the W and Z° particles. 

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