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  • Introduction to the Gas Laws
  • The Flow of Gases in Leaks
    • Viscous Flow
    • Types of Flow
    • Turbulent Flow
    • Laminar Flow
    • Calculation of an example
    • Viscosity of some gases
    • Conversion of helium leak rate at laminar flow to leak rates of other Gases
    • Molecular Flow
    • Conversion of helium leak rate to air leak rate
    • Conversion from weight leak rate to volume leak rate
    • Conversion of helium-leak rates at molecular flow to other gases
    • Transition flow
    • The Response Time
    • Example: Integral leak test on a heat-exchanger
    • The size of the leakrate signal after tn time constants in %
    • The Diffusion of Gases
    • Graham's Law of diffusion of Gases
    • Diffusion-Coefficients of some gases
    • Example: Diffusion of Search Gas in Air
    • Permeation
    • Helium Bombing Test
  • Helium Leak test on Heat Exchangers
  • Leak Detection and Measuring Methods
  • Leak Detection with Tracer Gas Methods
  • Leak Test with Laser Beam
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The Response Time

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The response times mentioned on datasheets and specifications of leak detectors are the individual response times of the leak detectors without any test piece connected, or with just the reference leak connected and are valid only for leaktests with test pieces with very small volumes. The response time of a test arrangement is given by the volume divided by the effective pumping speed of the used pumps:

\tau = \frac{V \, \textup{[Liter]}}{S \, \textup{[Liter/Sek]}}= \, [s]

The following formula describes the increase of the leak rate signal:

q_t = \left(1-e^{-\frac{t}{\tau}} \right)

and the following formula describes the decrease of the signal:

q_t = \left(e^{-\frac{t}{\tau}} \right)

 
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