Standard Ingress Protection Test Methods for Sensor Housings
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Mass Spectrometry Helium Leak Rate
Flow Quantification
Helium mass spectrometry measures the rate of tracer gas flow through microscopic paths in a sealed enclosure. The mass spectrometry helium leak rate represents the precise volume of helium escaping from a component per unit of time under a specified pressure differential. This measurement is required for verifying the hermeticity of electronic housings, vacuum systems, and sealed sensors.
Instrumentation Method
Ionization and separation are used to isolate helium ions from other gases based on their mass-to-charge ratio. During measurement, a mass spectrometry helium leak rate is determined by directing the gas sample into an ionization chamber, where the helium atoms are ionized and accelerated through a magnetic field. This field bends the path of the ions, focusing only the helium ions onto a collector where they are measured as an electrical current.
The magnitude of this current is directly proportional to the flow rate of the tracer gas, providing a continuous, real-time measurement of the leak size.
Calibration Requirement
Reference standard comparison is essential to convert the electrical current measured by the detector into a standardized leak rate. A mass spectrometry helium leak rate measurement must be calibrated using a reference standard that has been verified against national standards. This calibration adjusts the sensitivity of the system to account for variations in temperature and vacuum pressure.
Leak Significance
Boundary definition ensures that the measured leak rate is within acceptable limits for the specific application. A typical limit for high-reliability electronics is ten to the minus eight millibar liters per second, and any mass spectrometry helium leak rate above this threshold indicates a seal defect.