990 CLD Autoline™ Leak Detector
3-4
DRAFT 2/2/04
Tuning Adjustments and Calibration Check
Each day, and as otherwise scheduled, properly tune the spectrometer tube helium
sensitivity. This is generally done by using a standard reference leak of known value, called
a calibrated leak. Two types of calibrated leaks are available: those with a helium reservoir*
and those that operate on the capillary principle and require a helium source from the user.
* The calibrated leak contains a reservoir of helium which permeates through an
internal glass barrier at a very low constant rate, whether the built-in valve is open or
closed. Leave the valve open to prevent helium build-up and a sudden burst of helium
on valve opening. This valve permit a zero check when using the calibrated leak and
verifies the helium peak (but not adjacent peaks).
Vacuum Technologies:
❑
Calibrated leaks with a helium reservoir have constant leak rates in the ranges of
10
−
7
and 10
−
8
std cc/sec.
❑
Calibrated leaks operating on the capillary principle have constant leak rates of 10
−
3
,
10
−
4
, 10
−
5
, and 10
−
6
std cc/sec.
❑
Tuning leaks are generally have an approximate leak rate signal of 10
-
6 std cc/sec at
100 milliTorr test port pressure.
Sensitivity
The range of the exponent display is preset at the factory to agree with the sensitivity of the
system when the SENSITIVITY switch, located on the secondary front panel, is set to HIGH.
When this SENSITIVITY switch is set from HIGH to LOW, the system's sensitivity is lowered
by a factor of ten. However, the exponent range does not automatically reflect this
sensitivity change and must be manually set.
Example
The system is operating at high sensitivity, and the exponent range is 10
−
8
, 10
−
7
, 10
−
6
,
and 10
−
5
. If the controller is switched to low sensitivity, set the display's exponent range
by decreasing the number on the RANGE SELECT switch from 5 to 4. The range of the
exponent display is now 10
−
7
, 10
−
6
, 10
−
5
, and 10
−
4
(Table 3-3 on page 3-12).
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