The hot-filament ionization gauge is widely used for measuring the level of vacuum. The electrons are emitted from a hot cathode and accelerated towards the anode. In that process the electron may ionize a gas molecule. That gas molecule is pulled towards the collector and ion current is measured with an ammeter.
The Penning Ionization Gauge, also known as cold cathode gauge is used to measure the level of vacuum. High voltage between the anode and the cathode causes gas discharge and the resulting ionic current is measured with an ammeter. The measured amperes are then converted into pressure units such as Pascals or Torrs.
The thermocouple gauge is a device used to measure low vacuum. A filament is heated up by passing a current through it. When gas molecules interact with the filament, heat is carried away. Therefore higher pressure in the chamber means that more heat is taken away. The temperature of the filament can be measured with a thermocouple where the generated voltage depends on the temperature. Therefore in this system the voltage of the thermocouple is measured and converted into pressure units like millibars or pascals.
The Pirani Gauge is used to measure low vacuum. In the system tungsten filaments are heated up by passing current through them. As gas molecules interact with the filament, heat is carried away and electrical resistance changes. Therefore if the measured current or voltage can be converted into pressure units.
Turbomolecular pump ( #TMP ) is a popular high vacuum pump, that is widely used in many vacuum systems (electron microscopes for example) as it is clean, fast and efficient for maintaining high vacuum over a long period of time. Inside the pump there are rotor blades that rotate with a speed up to 90 000 rotations per minute and stator blades that are stationary. If a gas molecule enters the pump then it is hit by the rotor blades that are tilted at a certain angle. The kinetic energy from the blade is transfered to the gas molecule and causes it to move down and hit a stator blade that is also tilted at a certain angle, causing the molecule to „bounce“ down, where it meets the next rotor blade. Eventually the gas molecules reach the bottom of the turbomolecular pump where they are removed with a backing pump (prevacuum pump). The turbomolecular pump usually also needs a pre-vacuum before it can work efficiently and this can be done with a pre-vacuum pump (for example a scroll compressor pump). Once the pressure is low enough, the #turbomolecularpump starts working and the rotation speed of the rotor blades is gradually increased.
Vacuum can be understood as space from where matter (for example air) has been removed. It naturally exists in outer space but for certain applications, like materials characterization techniques, it needs to be achieved artificially. The desired level of vacuum is obtained with the help of a suitable vacuum pump. For example low vacuum (low quality vacuum with higher pressure) can be generated with a diffusion pump, scroll compressor pump, rotary vane pump, diaphragm pump or a sorption pump. High vacuum (high quality vacuum with very low pressures) however, can be obtained with high vacuum pumps such as the turbomolecular pump, ion pump, titanium sublimation pump and cryopump. The level of vacuum is measured with devices called vacuum gauges (vacuum meters) like the thermocouple gauge, pirani gauge, penning ionization gauge and the quadrupole mass spectrometer (analyzer). The working principle of vacuum pumps and vacuum gauges is explained with 3D animations in the video lecture above.