Helium Mass Spectrometer Leak Detector

Content
1. What is helium mass spectrometer leak detector?
2. Application of helium mass spectrometer leak detector
3. Helium mass spectrometer leak detector working principle
4. Structure of helium mass spectrometer leak detector
5. Types of helium mass spectrometer leak detector
6. Leak detection method of helium mass spectrometer leak detector
7. How to maintain helium mass spectrometer leak detector?
8. How to order helium mass spectrometer leak detector?

Helium mass spectrometer leak detector is a mass spectrometer that uses helium or hydrogen as a leak detection gas and a gas analyzer to detect helium gas for leak detection. Helium has low background noise, a low molecular weight, and a low viscosity coefficient, which makes it easy to pass through leaky holes and diffuse. In addition, helium is an inert gas and does not corrode equipment, so it is often used as a leak detection gas. If there is a leak in the container, the analyzer will respond to the leak and will know where the leak is and how much gas is leaking.

The application of helium mass spectrometry leak detector has been from the Academy of Sciences, universities and colleges, laboratories, and a few scientific research institutions to industrial and mining enterprises, and even township enterprises, and individual enterprises, it can be said that the application field is relatively wide.
Aerospace high-tech industry
Helium mass spectrometer leak detectors can be used in the aerospace high-tech industry, such as rocket engines and attitude engines, which used to be leak detected by brushing soapy water under pressure, but now the process has been improved again by using a helium leak detector. The rocket body leak detection uses a combination of several methods such as a positive pressure suction gun, helium hood method, and cumulative set method. Due to the application of leak detection technology, the sensitivity of leak detection is improved, which makes up for the low sensitivity of the instrument when the inhalation method is used for leak detection.

Vacuum industry, instrumentation, instrumentation industry
Pipelines, joints, valves, bellows, various vacuum pumps, various exhaust units, electron mirrors, mass spectrometers, electron beam ion velocity bursters, laser axis separators, high energy gas pedals, medical gas pedals, irradiation gas pedals, coating machines, thin film vacuum meters.

Electronics industry
Microwave transmitter tubes, electronic tubes, transistors, integrated circuits, sealed relays, various sensors, and cardiac pacemakers.

The working principle of helium mass spectrometer leak detector is that when a charged mass (positive ion) enters an analyzer with velocity v in a uniform magnetic field, it moves in a circle if the direction of velocity v is perpendicular to the direction of magnetic field H. When the magnetic flux density of the magnetic field is certain, ions with different mass-to-charge ratios (m/e) have corresponding transport radii in the magnetic field, that is, they all have corresponding circular trajectories, so that charged particles with different mass-to-charge ratios will be separated from each other after moving in the analyzer of the magnetic field. If a slit is placed in the path of the ions and the other ions are removed from the path, and a slit is opened in the corresponding radius of the helium ion, and an ion receiving pole is placed behind the slit, only the helium ions can pass through the slit and be received by the receiving pole to form a helium ion flow, which is amplified by the amplifier and indicated by the measuring instrument. When the leak is detected, if the leak is blown with helium gas, the helium gas will enter the mass spectrometry chamber of the leak detector through the leak, so that the measuring instrument of the leak detector will immediately respond sensitively and achieve the purpose of leak detection.

Helium mass spectrometer leak detector is mainly composed of vacuum system, electrical system, mass spectrometry chamber and other parts, sometimes it also needs to be equipped with auxiliary vacuum system.

Vacuum system
The vacuum system is what provides the conditions for the proper operation of the mass spectrometry chamber. A high vacuum system is necessary because a vacuum of 0.001-0.01 Pa is required for the normal operation of the tungsten cathode and to ensure a high transmission rate for the movement of helium ions in the analyzer. The energy saving valve in the system is designed to meet the regulation of the operating pressure in the mass spectrometry chamber. The valve has the highest leak detection sensitivity when fully open, so it is advisable to open it as wide as possible. In order to calibrate the leak detection sensitivity during leak detection, a standard leak hole is set in the system.

Configuration of auxiliary vacuum system
In helium mass spectrometer leak detection technology, according to the structure of the inspected parts, size requirements, and specific leak detection conditions, it is very necessary to set up auxiliary vacuum systems with the functions of pre-pumping the inspected parts, ensuring the working vacuum of the leak detector, performing gas shunting, shortening the reaction time and removal time, reducing the adverse effects on sensitivity, etc. under certain conditions.

Electrical system
The core of the electrical part of the helium mass spectrometer is the power supply and measurement of the mass spectrometry chamber, other parts include the power and control part of the vacuum system, the manipulation panel, the output instrument, etc. It mainly contains a small current amplifier and output device, low-frequency generator, high voltage rectifier and emission current stabilization device, and high voltage rectifier supplying cold cathode magnetron gauge power.

Mass spectrometry chamber
In general, the mass spectrometry chamber is the heart of the helium mass spectrometer and consists of the ion source, the analyzer, and the electrical system, and the cold cathode magnetron gauge is also placed in it to share its magnetic field. To facilitate the amplification of tiny particle streams, the high resistance and electrostatic gauge tubes for primary amplification are also placed within the mass spectrometry chamber. The mass spectrometry chamber shell is made of non-magnetic material, and the interior is hollowed out, while the exterior is set up as a magnet to form the magnetic field of the magnetic analyzer.

Single-stage magnetic deflection type helium mass spectrometer has an ion source consisting of a filament, a dissociation chamber and an ion gas pedal, an analyzer consisting of an applied uniform magnetic field, a baffle and an exit gap, a collector consisting of a suppression grid, a collection pole and a high resistance, and a first-stage amplified electrostatic tube and a cold cathode ionization gauge.
In the ionization chamber, the gas is ionized into positive ions, and the ions are focused into a beam under the action of an electric field. And in the accelerating voltage under the action of a certain speed through the gap in the accelerator S1 into the analyzer. Under the action of the uniform magnetic field, the ions with a certain speed will move in a circular trajectory.

In a double-stage tandem magnetic deflection type helium mass spectrometer, the chance of non-helium ions reaching the collector is reduced due to two analyses. And, if an accelerating electric field is set in the middle of the two analyzers, i.e., between the middle slit S2 in the figure and the adjacent baffle, the ions are accelerated again before entering the second analyzer. Those non-helium ions with the same momentum as helium ions can pass through the first analyzer, but, after entering the second analyzer by the second acceleration, they are separated due to the difference in their momentum from that of helium ions. As a result of the second separation, the background and background noise of the instrument are significantly reduced, improving the sensitivity of the instrument.

Counterflow helium mass spectrometer is based on the principle that the compression ratio of an oil diffusion pump or molecular pump is related to the type of gas. During leak detection, the helium gas that enters the front part of the main pump through the leak hole on the part to be tested is still partially returned to the mass spectrometry chamber, and the output of the instrument indicates the leak signal. This is the working principle of the counterflow helium mass spectrometer.

Determining the leak point type is both to determine the location of the specific leak point or leak hole of the component to be inspected, which is more common in large components or large parts, such as satellites, missile bodies, warheads, gas pipelines, gas tanks, oil tanks, boilers.

This is the most commonly used method, generally used for detecting relatively small parts. After vacuuming the device and the instrument, helium is sprayed with a gun at the place where the device may leak (e.g. sealing joints, welds, etc.). To accurately spray helium at the location of the leak, the helium should be sprayed from top to bottom, from near to far (relative to the leak detector position), because the helium may be sucked in by the leak above when spraying below, making it difficult to determine the location of the leak. Therefore, the helium should be sprayed from the side close to the leak detector first, from near to far.

The helium suction method is mainly used to check certain large sealed containers. Such as missile hulls, warheads, gas tanks, oil tanks, etc. The container is first evacuated and then filled with helium gas, which can be used in low concentration to save helium. A rubber tube is attached to the inlet flange of the helium leak detector, and a capillary tube with a small diameter is attached to the front of the rubber tube, so that the capillary tube moves around the welds and sealing joints on the outer wall of the helium-filled container.

The leak rate determination method is mainly used for testing components with strict sealing requirements, such as spacecraft, rocket liquid fuel tanks, satellites, electronic components, etc. This method can only test the leakage rate of the test piece, but cannot determine the location of the leakage holes and the number of leakage holes.

The helium filling method, also known as the negative pressure method, involves a closed gas chamber connected to a vacuum pump and a helium tank. If there is a leak in the small device surrounded by helium, the helium is slowly filled into the small device. The chamber is then opened, the device is removed, and the compressed air is used to blow off any helium that may be adsorbed on the outer surface.
The devices are then loaded one by one (or in groups) into a container connected to the inlet flange of the leak detector, the container is emptied and the throttle valve is opened, the helium originally entering the device will then be released through the leak hole and the leak detector will give a leak rate response.

Connect the helium leak detector to the test piece with a vacuum rubber tube, cover the test piece with an airtight container, fill the container with helium gas, and the leak detector will start to detect the leak, and if there is a leak in the test piece, the instrument will show the leak rate; this method can measure the leak rate of missile liquid storage tanks. The leak rate of the tank can be measured by filling the helium cover with a standard leak detector.

1. Regularly check the oil level of the mechanical pump of the helium mass spectrometer leak detector, if it is insufficient, add it in time. If the mechanical pump oil is brown, brown, or smells mushy, it means the oil has deteriorated. At this time, the oil in the pump should be released, if necessary, first flush with new oil, and then inject new oil.

2. Regularly clean or replace the exhaust pipe of the mechanical pump. If you find a lot of oil droplets accumulated in the exhaust pipe, you can take it off from the inside of the instrument, then clean it, and then blow drying with hot air or natural drying.

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