Tyhjiömittausta

Tyhjiömittaus refers to the measurement of pressure within a vacuum. Vacuums are environments where the gas pressure is significantly lower than atmospheric pressure. Various instruments, known as vacuum gauges, are used to quantify this low pressure, typically measured in units like Pascals (Pa), millibars (mbar), Torr, or millimeters of mercury (mmHg). The specific type of gauge employed depends on the pressure range being measured, as different technologies are effective in different vacuum regimes.

Low vacuum ranges, often from atmospheric pressure down to 1 Pa, can be measured using Bourdon gauges, diaphragm gauges, or oil-filled manometers. For higher vacuum levels, typically from 100 Pa down to 10^-3 Pa, Pirani gauges and thermocouple gauges are commonly used. These gauges work by measuring the thermal conductivity of the residual gas, which decreases as pressure drops.

For very high vacuum (UHV) and ultra-high vacuum (UHV) ranges, extending below 10^-4 Pa, ionization gauges are necessary. Hot cathode ionization gauges (like Bayard-Alpert gauges) and cold cathode ionization gauges (like Penning gauges) operate by ionizing the residual gas molecules and measuring the resulting ion current, which is proportional to the pressure. Accurate tyhjiömittaus is crucial in numerous scientific and industrial applications, including semiconductor manufacturing, particle accelerators, thin-film deposition, and scientific research.