Cosmo LS-1866, Руководство по эксплуатации

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4 FEATURE SUMMARIES 15
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4.1.1 Theory of Master-Preset
The measured pressure change in a leak test typically contains both the true leakage and drift errors due to
adiabatic compression and change in the ambient temperature. The pressure change due to leak remains
consistent over time, while the drift errors tend to decrease over time until completely stabilized. The below
graph, Differential pressure change when DET timer is extended shows this. The Master-Preset uses the
drift (Master-Preset value) calculated from the differences in characteristics between drifts and true leakage
to compensate for the leak test data for better detection accuracy
(See Section 8 → ).
4.1.2 Master-Preset operation
1) Master-Preset value calculation
The Master-Preset operation is executed by using an actual tested part. In this stage, D1 is measured
in the same measurement time as in a regular leak test. Then, the STB stage (stability time) is
initiated to equalize the pressure of the tested part and that of the master with each other through CHG
until drifts virtually no longer exist, when D2 is measured. The drift value (Master-Preset value) can be
determined by subtracting D2 (leak differential pressure) from D1 (drift value - leak differential pressure).
Master-Preset Value = D1 – D2
where
D1: measured leak rate value in DET (1)
D2: measured leak rate value in DET (2)
2) Compensation using a Master-Preset value in a leak test
Because the value that is detected in a regular leak test is equal to D1 shown above, a precise reading
of the leak rate can be provided by subtracting the Master-Preset value from DET value Δ P for
conformance judgement.
D = Δ P – Master-Preset Value
where
D: Differential pressure after compensation
∆ P: Differential pressure detected in the DET stage