14
3 LEAK TESTING OVERVIEW
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a) Required measurement timer increases under the following conditions:
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Test pressure is rather high.
•
Internal volume of the tested part is large.
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Surface area of the tested part is small
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Leak specification is small.
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Pressure deformation of the part and/or the clamp seal occurs
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Part temperature is different from the ambient temperature.
b) Setting CHG and BAL timers
Generally, a longer CHG timer reduces the ratio of noise presence in the DET stage, contributing to
better measurement accuracy. Set the timers with reference to the general timer ratios, suggested
below and the Table E).
General timer ratios: CHG timer
:
BAL timer = 3
:
1
In setting a CHG timer at installation and adjustment, first run a leak test with a sufficiently long CHG
timer setting. Then, start sampling data by gradually reducing the CHG timer to find out the shortest
CHG and BAL timers in which compliance data gets stabilized in the vicinity of zero.
c) Limitation on the BAL timer setting
A long BAL timer and a large leak limit setting during BAL initiates the DET stage without a large leak
being detected in this stage. In this case, the differential pressure exceeds its LIMIT before the DET
timer ends, resulting in a DPS output saturation. Further, when Leak Master differential pressures are
sampled to establish an equivalent internal volume (leak coefficient), too long a BAL timer can produce
a differential pressure past the measuring range, inhibiting measurement.
Too short a BAL timer, on the other hand, can give rise to differential pressure variations arising from
valve action as errors. Generally, a BAL timer between 1 and 5 seconds is recommended.
d) Setting the DET timer
Typical recommendation for the DET timer is from 2 to 10 seconds and those for the limit setting are
from ±10 to ±100 Pa in differential pressure terms. It is important to make the ratio of the CHG timer
as high as possible to the extent permitted by the limited measurement timer and to avoid indiscriminate
increases in the BAL and DET times. Even a short DET timer can provide a high degree of
detectability.
e) General guidelines for the setting of CHG and stabilization times
(0.01 to 0.1 MPa) (0.1 to 0.6 MPa)
The graph above does not include DET timer. DET timer varies
depending on the leak specifications.
NOTE
