A vacuum gauge is a device for measuring pressures significantly lower than atmospheric pressure. Various types of vacuum gauges exist, utilizing principles ranging from mechanical deflection to changes in the thermal or electrical properties of gases.
Vacuum means a space in a state of pressure lower than normal atmospheric pressure. Based on the pressure level, vacuum is typically classified into several ranges: low vacuum, medium vacuum, high vacuum, and ultra-high vacuum. Ultrahigh vacuum is the highest vacuum with the fewest gas molecules in space.
There are three primary principles for measuring vacuum: mechanical, gas transport, and ionization. The measurable pressure range and suitable applications vary depending on the principle used.
| Type | Pressure range (Pa) |
|---|---|
| Pirani vacuum gauge | 104 to 10-1 |
| Capacitance manometer | Atmospheric pressure (105) to 10-2 |
| Bayard-Alpert hot-cathode ionization gauge | 10-1 to 10-6 |
| Cold-cathode ionization vacuum gauge (Penning vacuum gauge) | 1 to 10-3 |
| Spinning rotor vacuum gauges | 1 to 10-4 |
A Pirani gauge consists of a heated metal filament suspended in a tube. The gauge operates on the principle that the thermal conductivity of a gas is dependent on its pressure in the low to medium vacuum range. As the pressure of the surrounding gas changes, so does the rate of heat loss from the filament. This change in filament temperature causes a corresponding change in its electrical resistance, which is then measured to determine the pressure.
- Related Words:
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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