Helium leak detection is one of the most widely used methods of nondestructive testing in use today. Current applications of helium leak detectors and helium leak sniffer span a diverse field of products and industry. Bio-tech companies use helium leak detectors to test implantable medical devices such as pacemakers to insure that the outer packages are protected from bodily fluids and to protect patients from possible contamination from leaking batteries and other materials. Automobile manufacturers use helium leak detection technology to test items such as air bag initiators, radiators and air conditioning units. Semiconductor fabs are littered with leak detectors used to leak test process equipment. Helium leak detector used in leak testing is the most sensitive method to detect leaks, before they reach the critical stage, available to industry today. Helium is the lightest inert gas. It is non-toxic, non-hazardous, non-destructive, and it easily penetrates small leaks. As helium has one of the smallest molecular size, it is able to pass through leak openings before they become large enough to leak other hazardous materials such as chlorine. Leak testing by helium leak sniffer can accurately detect and measure leaks which are 1000 times smaller than could be located by conventional non-destructive testing procedures such as liquid penetrant, acoustic (ultrasonic), and air bubble testing (vacuum box). The equipment can be calibrated to detect a leak which would leak the equivalent of one drop of water per month. Application as A Leak Detector Helium leak detector such as the Mass Spectrometer Leak Detector (MSLD) consists of a spectrometer tube, the electronics to operate it and interpret its output, and a high vacuum system to maintain proper vacuum. Means are also provided for connecting a test object, and a roughing vacuum pump. A system of valves is provided to evacuate the test object for connection to the spectrometer tube. If the subject item is a sealed object containing helium, the MSLD can be equipped with a vacuum chamber to contain the test object and thereby measure the leak rate of the sealed object. The Reason for Vacuum The purpose of the vacuum system is to support operation of the spectrometer tube. Helium molecules entering through a leak individually reach the spectrometer tube in a few milliseconds. Helium molecules, as well as molecules of other gases are continuously removed by the vacuum systems diffusing pump. If helium is continuously applied to a leak, the concentration in the spectrometer tube will rise sharply at first. Then it will reach equilibrium when it is being pumped out at the same rate as it is entering. When helium is completely removed from the leak the input will drop to zero while the residual helium is pumped out of the system. A leak is indicated by a rise in output signal of the spectrometer tube. The Spectrometer Tube In addition to the electrometer, the electronics also provide suitable voltages to operate the spectrometer tube and control the instrumentation of the vacuum system. Test pieces are generally pumped down by a separate mechanical vacuum pump before they are connected to the spectrometer tube. This prevents over-loading the vacuum pumping system.
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