Vacuum Measurement Techniques

The force exerted per unit area.

Measured relative to a perfect vacuum; the pressure in outer space is close to zero absolute pressure.

Measured relative to atmospheric pressure; the pressure in a car tire gauge reading.

Pressure below atmospheric pressure; commonly found in vacuum chambers.

Measures the total pressure, including atmospheric pressure.

Measures pressure relative to atmospheric pressure.

A device used to measure pressure in different reference modes.

The ratio of the force applied over the area it acts on.

The force exerted by a liquid column due to its weight.

The total pressure of a mixture of gases is equal to the sum of the partial pressures of each gas.

A method of pressure measurement that directly measures the force exerted on a surface.

A method of pressure measurement that indirectly measures pressure by using properties like thermal conductivity or ionization.

The change in thermal conductivity of a gas is proportional to its pressure.

Gas molecules are ionized and the ion current is proportional to the pressure.

A gauge that measures pressure below atmospheric pressure (vacuum pressure).

A type of thermal conductivity gauge that uses a heated filament to measure pressure. These gauges are commonly used in vacuum systems to measure low to medium vacuum.

A gauge used to measure vacuum pressure that is based on the principle that the temperature difference between two junctions of a thermocouple depends on the pressure of the surrounding gas.

A type of vacuum gauge that uses a diaphragm to measure pressure differences. These gauges are often used to measure medium to high vacuum pressures.

The ion current (ic) in a vacuum gauge is directly proportional to the electron emission current (ie) and the pressure (P) within the vacuum system.

The electron emission current (ie) is a critical parameter in ionization gauges, directly affecting the ion current and thus the pressure measurement.

The constant K in the ionization gauge equation represents the efficiency of the ionization process, factoring in factors like the type of gas and the geometry of the gauge.

A hot cathode ionization gauge utilizes a heated filament (cathode) to emit electrons, leading to ionization of gas molecules in the vacuum chamber.

To ionize gas molecules effectively, electrons in an ionization gauge are accelerated to specific energies, achieving efficient ionization within the vacuum system.

The work function (W) represents the minimum energy required to extract an electron from a material's surface, crucial for understanding electron emission in ionization gauges.

Ultra-high vacuum (UHV) systems necessitate specialized components like stainless steel chambers, CF flanges, view ports, and valves to maintain a high vacuum level.

Designing for UHV involves selecting materials with low outgassing rates (like stainless steel), employing bake-out procedures to reduce residual gases, and providing multiple ports for gauges, sample transfer, and other equipment.

Measures pressure by compressing a gas into a smaller volume and using the ideal gas law to calculate pressure. Useful for measuring low pressures down to 10^-6 Torr. Uses mercury as the working fluid.

Measures the resistance change of a heated filament due to the surrounding gas pressure. The filament cools down faster at lower gas densities, resulting in a higher resistance. Range: 0.5 Torr down to 10^-4 Torr.

Measures the temperature of a heated filament using a thermocouple. The temperature of the filament is directly proportional to the surrounding gas pressure. Range: 10^-3 Torr to 10^-1 Torr.

A vacuum gauge with a cold cathode that releases electrons to ionize the gas. The current generated by the ionization is directly proportional to the pressure. Can measure pressures down to 10^-7 Torr.

A specialized ionization gauge with a fine collector wire that minimizes X-ray-induced errors. The current from ionized molecules is directly proportional to pressure. Can measure pressures as low as 10^-8 Torr.

The pressure of the gas changes the heat dissipation from a hot filament within the sensor. The heat loss from the filament is directly proportional to the gas pressure.

A gauge that utilizes the deformation of a diaphragm caused by pressure differences. Examples include Bourdon tubes, bellows, and capacitance manometers.

The relationship between the pressure and the current generated by the ionization is dependent on the type of gas used. This means the sensitivity can change with the type of gas.