In World War II, helium mass spectrometry was used in Uranium enrichment plants for leak detection. This approach is still in use today, with some adjustments, as it is regarded to be one of the most accurate ways for locating leaks. Helium gas is utilized in this approach as a tracer gas. This occurs when helium leaks in/out of the tested product and enters the detector, where its partial pressure is recorded and shown on a screen. Leakage is detected using an instrument called a Helium Mass Spectrometer, which also measures the rate of leakage.
Principle of helium leak detector
Leak Detector works on the concept of a sector field mass spectrometer. Containers that need to be tested for leakage are usually filled with Helium and put in a vacuum chamber. The tracer gas helium is ionized in a vacuum after analysis. With the addition of voltage, helium ions are accelerated and then separated in a magnetic field. Using a particular detector, the ion current is converted to an electric current. Leak detecting units accelerate the current and display it on the screen. Helium concentration determines the measured current, which is equivalent to the measured leak.
What makes helium suitable for leak detection?
Due to its numerous advantages, helium is the ideal choice for leak detection purposes.
- Non-toxic and non-flammable
- Inert and non-condensed
- Low cost
- Due to its low atomic mass, it can easily pass through even very small leaks
- Present in the atmosphere, only in trace amount
Leak detection methods using helium mass spectrometer
There are two primary methods of testing: vacuum testing and pressure testing. The goal is to find the leak and determine how much or how fast it is leaking. When using either technique, it's vital to maintain circumstances that are comparable to what the system would encounter in real life.
As part of the vacuum testing, the leak detector is inserted into the system or product that has to be tested for leaks. In order to remove air from a system and create a vacuum, a pump is utilized. Helium is then sprayed on locations where the leakage is likely to occur. Spraying should be done with proper care to ensure that no portion of the body is skipped. As soon as the detector detects a leak of Helium, it alerts the user. This approach is also known as the spray probe method, or the spray probe technique.
Under pressure testing, the product must be placed within a vacuum chamber that has been properly constructed. Helium is pumped into the chamber, and the detector is used to check for leaks. This method is also known as the sniffer probe method. Helium filled system put in a chamber with a detector attached to a vacuum pump is another mode of this approach for determining leakage rate. If there is a leak, Helium will leak out of the pump and the detector will calculate the rate of leaking once the pump is running.
Helium mass spectrometry can be used in a variety of ways to discover extremely small leaks.
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