Vacuum Gauges

Capacitive gauges, also known as capacitance manometers, measure vacuum independently of the gas type. These gauges use a flexible diaphragm that responds to the differential pressure between the vacuum being measured and a stable reference vacuum. As the pressure in the vacuum chamber changes, the diaphragm bends slightly. This bending alters the distance between the diaphragm and a fixed electrode, which changes the electrical capacitance between them. The gauge measures this capacitance change and converts it into an exact pressure reading.

Capacitive gauges cover a wide pressure range, from medium to high vacuum. They are particularly suitable for applications requiring precise process control, such as thin-film deposition, calibration tasks, or measurement of corrosive gases, where reliable, gas-independent readings are essential for consistent results.

Piezoresistive gauges also rely on the mechanical deflection of a diaphragm, but instead of capacitance, they detect changes in electrical resistance caused by strain. When pressure changes in the vacuum chamber, the diaphragm bends slightly, causing a mechanical strain in the sensor element. This strain changes the electrical resistance of the element, which the gauge measures and converts into a precise pressure reading.

Piezoresistive gauges are gas-independent. They are particularly suited for applications in the rough to medium vacuum range, including industrial processes, backing pump monitoring, and general process control.

Pirani gauges measure vacuum by detecting how effectively gases conduct heat. At the heart of the gauge is a small, heated filament whose temperature changes depending on the surrounding gas density. When more gas molecules are present, they absorb more heat from the filament, causing its temperature to drop. Conversely, the higher the vacuum, the fewer molecules are available to carry away heat, so the filament stays hotter. The gauge measures these temperature changes and converts them into a pressure reading.

Because the heat conduction depends on the type of gas, Pirani gauges are gas-dependent. They are ideal for the rough to high vacuum range, making them suitable for a wide variety of applications, including leak detection, freeze-drying, coating, and industrial vacuum systems.

Cold cathode gauges, also known as Penning gauges, measure pressure by ionizing gas molecules inside the gauge. The sensor consists of two electrodes and a strong magnetic field. When a high voltage is applied, free electrons are accelerated and start spiraling between the electrodes. As they move, they collide with gas molecules and knock out more electrons, creating positive ions.

The number of ions formed depends on how many gas molecules are present – in other words, on the pressure inside the chamber. At low vacuum levels, more gas molecules are available, so more ions are produced, resulting in a stronger ion current. At high vacuum levels, the gas density decreases, fewer ions are generated, and the current drops. The gauge converts this ion current into a pressure reading.

Because each gas ionizes differently, cold cathode gauges are gas-dependent. They are ideal for the high and ultra-high vacuum range. Typical applications include scientific research, particle accelerator technology, coating systems, and semiconductor processes, where reliable and precise pressure measurement in extreme vacuum conditions is critical.

Hot cathode gauges, most commonly in the Bayard-Alpert design, use a heated filament to emit electrons, unlike cold cathode gauges, which rely on free electrons accelerated in a magnetic field. These electrons are accelerated toward a positively charged grid, where they collide with gas molecules and knock out additional electrons, creating positive ions. Like cold cathode gauges, the number of ions produced depends on how many gas molecules are present. This ion current is measured and converted into a pressure reading.

Hot cathode gauges are gas-dependent and provide precision in the ultra-high to extremely high vacuum range, making them particularly suitable for scientific research, semiconductor manufacturing, and demanding analytical applications.

A vacuum gauge – also called a vacuum meter or vacuum manometer – is a device used to measure the pressure. It provides readings of total pressure, from rough to ultra-high vacuum, making it essential for monitoring, controlling, and maintaining vacuum processes.

Different gauges are required, depending on the type of vacuum system and the vacuum level. Typical applications where gauges are used include industrial vacuum processes, leak detection, freeze drying, coating technology, semiconductor manufacturing, and scientific research.

Each vacuum gauge operates based on a different physical measurement principle, making certain gauges better suited to specific applications. The pressure range a gauge can accurately measure depends both on the underlying measurement principle and on the design of the gauge itself, ensuring optimal performance for the intended process conditions.

The following factors must be considered when choosing a vacuum gauge:

Vacuum gauges work with direct or indirect measurement principles.

Both Pirani and thermocouple gauges are thermal conductivity gauges, meaning they measure vacuum by monitoring how quickly a heated wire loses heat to the surrounding gas. The key difference is how the cooling of the wire is measured:

There are no strict regulations or general recommendations for recalibration. The need depends on your process requirements, the media used, and the type of gauge. Many customers choose intervals of six months or one year.

Unsure if your gauge needs recalibration? Find out more about the Pfeiffer calibration service or get in touch with our service experts right now!

In most vacuum systems, a single gauge cannot measure the entire pressure range. To get accurate readings at all pressures, multiple gauges or combination gauges that use different measurement principles can be installed in the same system.

Choosing the right type and combination of gauges ensures reliable and precise pressure monitoring across the full range. It allows operators to control the entire process accurately, from pumping down the chamber to reintroducing gases.

Available combination gauges:

You can find step-by-step instructions, helpful tips, and a checklist to guide you through the proper cleaning and maintenance of vacuum gauges in our whitepaper.

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