A vacuum gauge is a device used to measure pressures significantly below atmospheric pressure. These instruments utilize various physical principles, ranging from mechanical deflection to changes in the thermal or electrical properties of gases.
A vacuum is defined as a space where the pressure is lower than standard atmospheric pressure. Vacuum levels are typically categorized into four ranges based on pressure: low, medium, high, and ultra-high vacuum.
Vacuum measurement generally relies on three primary principles: mechanical force, thermal conductivity, and gas ionization. The optimal measurement method depends on the target pressure range and application requirements.
| Type | Pressure Range (Pa) |
|---|---|
| Pirani vacuum gauge | 105 to 10-1 |
| Capacitance manometer | Atmospheric pressure (105) to 10-2 |
| Bayard-Alpert hot-cathode ionization gauge | 10-2 to 10-8 |
| Cold-cathode ionization vacuum gauge (Penning gauge) | 10-1 to 10-7 |
| Spinning rotor vacuum gauge | 1 to 10-5 |
A Pirani gauge utilizes a heated metal filament suspended within a tube. It operates on the principle that gas thermal conductivity correlates with pressure in the low-to-medium vacuum range. As the pressure of the surrounding gas changes, the rate of heat loss from the filament shifts. This alters the filament's temperature and electrical resistance, which is measured to determine the pressure level.
- Related Terms:
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- Vacuum gauge
- Pirani vacuum gauge
- Capacitance manometer
- Bayard-Alpert hot-cathode ionization gauge
- Cold-cathode ionization vacuum gauge (Penning vacuum gauge)
- Spinning rotor vacuum gauge
- Piezo vacuum gauge
- Ionization vacuum gauge
- Cold cathode
- Hot cathode