An Introduction To Helium Leak Detection Technology Darrell R. Morrow, PhD Leak Detection...
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Transcript of An Introduction To Helium Leak Detection Technology Darrell R. Morrow, PhD Leak Detection...
An Introduction ToHelium Leak Detection
Technology
An Introduction ToHelium Leak Detection
Technology
Darrell R. Morrow, PhD
Leak Detection Associates, Inc.Blackwood, New Jersey
Why Helium? Low Background (5-20 PPM)Low Background (5-20 PPM) InertInert SafeSafe LightLight Low CostLow Cost
?
He N
O
FNe
Cl
Ar
Kr
Xe
H
Why A Helium Leak Detector?
SIMS 180TD+
High SensitivityHigh Sensitivity Wide RangeWide Range ReliableReliable QuantitativeQuantitative Dynamic TestingDynamic Testing NIST TraceableNIST Traceable
Analyzer Cell180o Deflection
+200VVAR.
FILAMENT
GROUND
TRIODE PLATEHEAVY IONS
HELIUM IONS
LIGHT IONS
REPELLER
HIGHPOWERSUPPLY
LOGAMPS
- +TARGET
RESISTANCE
HIGHVACUUMGAUGE
GROUND
MAGNETMAGNET
Helium Leak Testing: Vacuum ModeHelium Leak Testing: Vacuum Mode
The “hard” vacuum test procedure measures the package’s cumulative leak rate arising from all sources within the sample.
This method enables the barrier performance of seals to be quantified.
Helium Leak Testing: Sniffer ModeHelium Leak Testing: Sniffer Mode Individual packages containing helium can be
checked for leaks using a pencil-sized vacuum collector (sniffer) attached to a helium leak detector.
The rate of gas sampling (flow rate) is set at 1cc/second; enabling a (ambient pressure) leak rate to be measured in ppm, or in cc/second.
The sniffer mode test procedure is “site-specific” in that the probe collects helium escaping within ~ 1/8” of the leak site.
Virtual Leaks and Outgassing
Virtual leaks are small trapped volumes of gas at atmospheric pressure within the vacuum envelope which communicates with the vacuum
system by means of minute crevices, cracks, grooves, etc.
Outgassing is the desorption of atmospheric gases and contamination from the surface area within the vacuum system.
Fine Leak Rate RealityTheoretical hole diameter calculation in molecular flow regime
D = M L 1 6Q 0 .33
2 RT P1-P2
CONDITIONS 1E-6 atm cc/sec. He leak rate 0.6 cm. wall thickness 20 C ambient temperature Inboard He spray test
D = 4 (.6)(1)(6E-6) 0.33
2 (8.32E7)(293)
Size (microns) .0001 .001 .01 .1 1 10 100 1,000 10,000
PollenMicrobes
LintTobacco smoke
Household dustIndustrial dust
Acid fumesGas molecules
Finger printsAlcohol residue
D = .0009 cm. = 0.9 microns
1 meter=
1,000,000 microns
Pharmaceutical/Device Package Test Methods
Leak Test Methods Principles The most common concept behind the
« rapid » detection of leaks in various packaging forms is the monitoring of changes in specific physical parameters such as fluid (gas/vapor/liquid) transport from one side of a « sealed » package to the other, such as bubble formation or pressure changes.