16
4 FEATURE SUMMARIES
4.1.3 When to execute a Master-Preset process
Master-Preset process is recommended under one of the following conditions:
1) Production part changeover
For production lines that produce multiple part models, each model should be assigned to a specific
leak tester channel. Therefore, a Master-Preset process is required on the new channel immediately
after the model changeover. Master-Preset is also required when switching parts with different volume
and/or test pressure in a same channel.
2) When test parameters such as test pressure and/or timer settings are changed.
3) When test environment changed
4) When No-Go judgments occur consecutively
The seals in the fixture may be damaged in this case, assuming that production line is unlikely to
produce consecutive defects. Since the test result of a Master-Preset process shows almost true
leakage, it would help in determining if these No-Go judgments are from leaks or from fluctuations due
to drift.
4
4
.
.
2
2
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L
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k
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b
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r
r
a
a
t
t
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(
(
P
P
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)
)
To obtain a volumetric leak rate, mL/min, the relationship between the pressure change caused by a leak
and the volume of leakage from the part must be known. The Leak Calibration feature gives a known leak
to the Work-side pneumatic that creates a measurable differential pressure in order to measure its
equivalent internal volume. The definition of internal equivalent volume (Ve) is the volume of air of the
entire Work-side pneumatic circuit at a particular test pressure. It also includes a diaphragm deformation
factor of the DPS. Ve is used as leak coefficient K(Ve) in the leak rate calculation.
Once equivalent internal volume is measured, the differential pressure detected in the leak test DET stage
can be displayed in mL/min (See Section 9.1.
a) Measuring equivalent internal volume using a Leak Master
Leak calibration is normally carried out using a Leak Master (reference leak generator). The
equivalent internal volume is calculated from the Leak Master flow rate and the measured differential
pressure.
b) Measuring equivalent internal volume using a Leak Calibrator
When using a Leak Calibrator to determine an equivalent internal volume, convert the volume change
measured during the DET stage into a volumetric leak rate under the atmospheric pressure by using the
following equation and enter it.
Where:
Q:
Value to input in mL/min (Leak rate corresponding to the volume
change)
∆
V:
Volume change (mL)
P:
Test pressure (kPa)
T:
DET timer
c) Sampling compensation values
It is necessary to measure only the differential pressure due to leak to determine the accurate
equivalent internal volume. To accomplish this, do a leak test with a known non-leaking part prior to
the leak test. The resulting measurement value is noted as a drift, by which the value measured in
leak calibration is compensated.
T
60
×
3
.
101
P
+
3
.
101
×
V
Δ
=
Q
