Detecting Leaks: Should You Use a Residential Gas Analyser (RGA)?

Posted by Joshua Miller on Nov 17, 2021 11:00:00 AM

Across many industries, leak detection technology is crucial to project success. In the space industry, for example, detection tools help pinpoint dangerous leaks that may cause rapid temperature changes and a loss of oxygen in spacecraft. 

Many engineers use Residual Gas Analysers (RGAs) to assess the leak-tightness condition of their vacuum chambers. Here, we compare RGAs with leak detectors before exploring whether you should use RGAs for your project.

How Do Leak Detectors Work?

Leak detectors identify, analyse, and measure any gases either entering or escaping an enclosed space or pressurised system.

Leak detectors are capable of discovering the source of a leak and how quickly substances enter or exit the system. Most leak detectors are tuned for and measure the presence of helium and have built-in vacuum technology. To measure helium, these detectors use 180° deflection ion mass spectrometry. Ionized particles in the vacuum are accelerated and add voltage to particles which are separated, or selected, within the magnetic field, transforming ions into an electric current.

How do Residual Gas Analysers Work?

While leak detectors search for helium, RGAs are used in high vacuums to look for all gases within a space. Generally, RGAs consist of the following three components: 

  1. Ion source — the ion source turns all the gas within a vacuum into ions. This is achieved through the emission of electrons from a hot filament. These accelerate toward the source using an electrical bias. The rapidly moving electrons collide with gas molecules, dislodging and ionising molecules. 
  2. Mass Filter — this is a quadrupole array composed of four stainless-steel rods. The quadrupole varies voltages to favour ions of a certain mass/charge ratio to transverse the quadrupole array when their presence is then detected. 
  3. Detector — ions within the filter collide with a metal plate called a detector, or Faraday cup. The ions become neutralised as the electrons transform into an electrical signal. The resulting current matches the current of the incoming ion. An election multiplier amplifies the signal and alerts researchers to their presence. This amplifier is extremely valuable, as it helps detect low-level gases that might otherwise go unnoticed.

What’s the difference between RGAs and Leak Detectors?

Both leak detectors and RGAs are mass spectrometers. However, RGAs are not built with their own vacuum system. As such, RGAs must be supported within a vacuum. 

The advantage of using an RGA is that they detect different gas types, while leak detectors only detect helium (or sometimes hydrogen). Being able to distinguish between gases is valuable when dealing with gas that is dispersed over a large area. In these cases, the more gas species you can detect, the easier it is to locate the leak source.

When Should You Use an RGA?

By detecting all gases, RGAs provide specific information about what is going in and out of a system. For complex, large, or low-tolerance systems, this information may be key to achieving ideal vacuum conditions.

The textile industry, for example, commonly uses physical vapour deposition (PVD) to create coatings. Having an RGA present helps engineers know if they are bringing in the right mix of elements for the required processes. 

Considering the greater depth of information that RGA provides, organisations looking to improve their vacuum performance may benefit from this tool.

 

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