Vacuum gages

Unterdruck-kessel, m. low-pressure boiler or tank. -messer, m. vacuometer, vacuum gage. 

Basic concepts discussed here are atmospheric pressure vacuum gage pressure absolute pressure Boyle s law or pressure/volume relationship Charles law or temper-ature/volume relationship combined effects of pressure, temperature and volume and generation of pressure or compression. 

It is helpful to understand the relationship of vacuum to the other pressure measurements. Vacuums can range from atmospheric pressure down to zero absolute pressure , representing a perfect vacuum (a theoretical condition involving the total removal of all gas molecules from a given volume). The amount of vacuum is measured with a device called a vacuum gage. 

It is a high-vacuum gage made up of two cathodes and one anode placed in a magnetic field produced by a permanent magnet (see Fig. 1.33). Electrons due to natural radioactivity or to field emission start a discharge in the gas. The presence of the magnetic field produces paths about 100 times longer than the distance between the electrodes. Positive ions are collected by the cathodes. 

Figure 1. Diagram of apparatus (M) monomer reservoir (F) flow meter (VG) vacuum gage (mercury manometer) (E) electrode (T) liquid nitrogen trap (P) mechanical pump (V,) needle valve (Vt) stop valve (Vs) pressure control valve (OSC) discharge frequency oscillator (AMP) amplifier (1MC) impedance matching circuit...

MCLEOD GAGE. A liquid-level vacuum gage in which a known volume of gas. at the pressure to he measured, is compressed by the movement of a liquid column to a much smaller known volume. a> which the resulting higher pressure is measured,... 

Pressure measurements involve the interaction of alpha radiations with a gas, which results in the formation of positive and negative ions. The latter can be collected and measured as electric current The number of ions produced in a gas by alpha particles depends upon the density and composition of the gas. Where either of these factors is known the other can be inferred from these measurements. Several vacuum gages employ this principle. 

When specifying and using vacuum gages, one must constantly keep in mind that atmospheric pressure is not constant and that it also vanes with elevation above sea level. 

Vacuum gages can be either direct or indirect reading. Those that measure pressure by calculating the force exerted by incident particles of gas are. direct reading, while instruments that record pressure by measuring a gas property that changes in a predictable manner with gas density are indirect reading. 

TABLE 2. RANGE OF OPERATION OF MAJOR VACUUM GAGES... 

Hot-Filament Ionization Vacuum Gage. This gage is the most widely used pressure-measuring device for the region from 10-2 to 10-n torn The operating principle of tins gage is illustrated in Fig. 5. 

Fig. 6. Philips cold-cathode ionization vacuum gage...

J.J. Sullivan, Research Efforts Boost Range and Accuracy of Vacuum Gages, ... 

Figure 3.1. A schema of the apparatus for the kinetic investigation of the gas evoiution. 1, the reaction vessel 2, vacuum gage 3, gutters for sampling of the gaseous products 4, vacuum cocks 5, the heating furnace with rectangular profiles of temperatures, high-temperature thermocouple 7, thermoregulator 8, ampule with sample.

If the vacuum gage does not read the manufacturer s no-load suction pressure, the jet is at fauit ... 

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