Edwards ELD500 Series, Instruction Manual

Page: 76 / 121

D13510840D - Calibrated leak - He 4-6
Page 66
In the laminar flow region it applies:

= dynamic viscosity
Some values of dynamic viscosity

in 10
-5
Pa s.
The resulting values must be used according to the predominant type of gas flow, i.e. for leak
rates lower than 10
-5
mbar Is
-1
mainly molecular flow and for leak rates higher than
10
-5
mbar Is
-1
mainly laminar flow can be assumed.
Adjustment of leak rate
The nominal leak rate was measured during production at a test gas pressure of 1 bara versus
a pressure of lower than 1 mbar at the connecting flange and is shown on the label. The
adjustment diagrams are valid for nominal leak rate of 5 x 10
-6
mbar ls ±10% for the CL - He
4-6. The leak rate is pressure dependent and can be found in Figures 49 or 50 . Upon request,
individual calibration of a single test leak as a function of the search-gas pressure can be made
in our factory at cost price.
If you suspect the nominal leak rate has changed after longer use, recalibration of the test
leak can be made in our factory against charge. When demanding higher accuracy Edwards
recommends a recalibration once a year.
If a calibration certificate is required, it can be issued by Service. Calibration and calibration
certificates are available to order, charges applicable.
The test leak rates depend on the adjusted pressure [bar rel], see
Figures 49 and 50 .
If a significant deviation from the nominal leak rate of 5 x 10
-6
mbar ls occurs, a factor can be
calculated based on the leak rate diagrams. The nominal leak rate is to be multiplied by this
factor.
Calculation of the factor:
He R 134a N2O2 Ar H2
h 1.96 1.36 1.82 2.21 0.88
q
x
q
He
--------

He

x
--------- =