vacuummeters

Vacuummeters, or vacuum gauges, are instruments that measure the pressure inside a vacuum system. They report absolute, gauge, or differential pressure and are used to monitor and control processes that require low pressures, as well as to characterize vacuum performance in research and industry.

Several families of vacuummeters exist, each based on different physical principles. Mechanical gauges include Bourdon-tube gauges for rough vacuum and McLeod gauges that use Boyle's law to derive pressure at very low levels. Thermal conductivity gauges, such as Pirani and thermocouple gauges, infer pressure from how the gas conducts heat away from a sensing element. Capacitance diaphragm gauges use the bending of a flexible diaphragm to determine pressure in the high-vacuum range. Ionization gauges, including hot-cathode (Bayard-Alpert) and cold-cathode (Penning) types, measure extremely low pressures by collecting ions produced when gas molecules are ionized by a strong electric field.

Vacuum instruments are typically calibrated to read in pascals, Torr, or millibars, and can be configured to report absolute pressure, gauge pressure, or differential pressure. In practice, different gauge types cover different vacuum ranges, with rough vacuum closer to atmospheric pressure and ultra-high vacuum at the lower end of the scale.

Applications span semiconductor fabrication, coatings and vacuum deposition, analytical instruments, cryogenics, and space-simulation chambers. Proper use includes avoiding gas contamination, ensuring leaks are sealed, and regularly calibrating the instrument for the expected gas composition and temperature.