Varian 990 dCLD II, Operation Manual

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Model 990 dCLD II Component Leak Detector
3-6
3.2 System Sensitivity and Configuration
During the process of installing the 990 dCLD II and building the associated vacuum sys-
tem, it is necessary to determine the sensitivity of the system. The 990 dCLD II is able to
measure four decades of leak rate signal at once for a given configuration. For example, in a
typical system with the V70D MacroTorr pump running at high speed, the four decades of
leak rate are 10
−
7
, 10
−
6
, 10
−
5
, and 10
−
4
. Running the V70D MacroTorr pump at slow speed
yields 10
−
8
, 10
−
7
, 10
−
6
, and 10
−
5
decades of leak rate. Table 3-1 shows the effects of pump
type and speed on the four decades of detectable leak rate. Table 3-1 shows the four
decades displayed for any given configuration and turbo speed setting.
Note: The underlined decade represents the variable set in TOP RANGE parameter.
The pumping speed of the backing pump and the conductance of the vacuum system also
play an important role in the determination of system sensitivity. A calibrated helium leak
on the as configured system must be used to characterize the leak rate measurements.
The 990 dCLD II must be set up to display the desired four (4) decades of leak rate
measurement by setting the Range (Top Range) and selecting the Turbo speed and Ranging
method. These and other parameters are discussed in the next section.
Table 3-1 Leak Rate Range for High Vacuum Pump Type and Speed Combinations
Turbo Speed Fast Turbo Speed Slow Maximum Test
Pressure
V70 Turbo Pump 10
−
8
, 10
−
7
, 10
−
6
, 10
−
5
10
−
9
, 10
−
8
, 10
−
7
, 10
−
6
100 mTorr
V70D MacroTorr Pump 10
−
7
, 10
−
6
, 10
−
5
, 10
−
4
10
−
8
, 10
−
7
, 10
−
6
, 10
−
5
3 Torr
V70LP MacroTorr Pump 10
−
6
, 10
−
5
, 10
−
4
, 10
−
3
10
−
7
, 10
−
6
, 10
−
5
, 10
−
4
5 Torr