An ionization vacuum gauge is a core component for measuring high vacuum. It determines the vacuum level by ionizing gas molecules and measuring the resulting ion flow. Based on the different ionization methods, it is mainly divided into the following two categories:
One. Hot Cathode Ionization Vacuum Gauge
Working Principle: A heated filament (cathode) emits thermionic electrons. These electrons gain sufficient energy as they fly towards the anode grid, colliding with gas molecules and ionizing them. The resulting ion current is measured at the collecting electrode; this current is proportional to the gas pressure.
Advantages: Accurate measurement, good stability, and excellent linearity; it is the mainstream choice for high vacuum measurements.
Disadvantages:
X-ray effect: Electrons striking the anode grid generate soft X-rays, which irradiate the collector electrode, triggering photoelectron emission and creating a pressure-independent "background current." This causes measured pressures to deviate from the true pressure under ultra-high vacuum (approximately <10⁻⁸ Pa).
Chemical removal: The high temperature of the filament causes reactive gas molecules (such as oxygen) to dissociate and be adsorbed, creating a "vacuum effect" that affects the actual pressure.
Filament burnout risk: Under higher pressures (e.g., >10⁻² Pa) or sudden exposure to the atmosphere, the incandescent filament is prone to oxidation and burnout.
Two. Cold Cathode Ionization Vacuum Gauge
Working Principle: Utilizing a high-voltage electric field to induce discharge in a vacuum (the cold cathode is unheated), and applying an external magnetic field. Electrons, under the combined influence of the electric and magnetic fields (Lorentz force), undergo helical motion, greatly increasing the probability of ionization through collisions with gas molecules, forming a self-sustaining plasma discharge. The ion flow is proportional to the pressure.
Advantages: Robust structure, no hot filament, resistant to atmospheric impact, long lifespan.
No X-ray background current limitation, allowing for the measurement of higher vacuum levels (typically on the order of 10⁻¹² Pa).
Disadvantages:
Discharge Stability: Discharge may be unstable at low pressures, even exhibiting "discharge delay" or "flameout" phenomena.
Sensitivity to Contamination: Contamination of the cathode surface can severely affect electron emission, leading to inaccurate measurements.
Strong Magnetic Field Interference: The vacuum gauge's own strong magnetic field may interfere with surrounding equipment (such as ion sources); installation location requires careful consideration.
