990 CLD Autoline™ Leak Detector
DR
AFT 2/2/04
1-3
OPTO-22 Modules
Spare OPTO-22 modules for 120 VAC units, or for input control voltages other than 120
VAC, can be ordered as listed in 1-3.
Test Cycle Description
The Vacuum Technologies 990 CLD leak detector (Figure 1-1) can detect leaks in the range
of 2 x 10
-10
cc/sec to 10 cc/sec, depending on high vacuum pump and mechanical pump
selection. Major assemblies which comprise the leak detector include a mass spectrometer
tube, a high vacuum pump, a main electronics console, and interconnecting wiring.
The test cycle occurs as follows:
1. When the high vacuum pump gets up to speed the spectrometer tube pressure is low
enough (
≤
2 x 10
-4
Torr*) to permit energizing of the ion-source filament in the
spectrometer tube. There are actually two filaments, but only one is energized at a time.
*1 Torr = 1000 milliTorr = 1/760 standard atmospheric pressure; hence,
10
-4
Torr is approximately 1/10,000,000 atmosphere. See 6“Fundamentals of Leak
Detection” for other conversions.
2. Helium is applied sparingly to the test object, such as from a spray probe.
If there is a leak in the test object, helium entering through the leak spreads to all
parts of the evacuated system. Some of this helium is exhausted through the
mechanical pump to atmosphere; the rest of the helium is diffused through the high
vacuum pump (against or
contra
the normal flow) and reaches the spectrometer tube.
The rate at which helium enters the spectrometer tube appears on the associated
horizontal bar graph display and can be monitored on an internal or optional
external loudspeaker, as desired.
As long as helium from the spray probe enters a leak in the test object, the leak rate
appears on the leak detector front panel. When the spray probe is removed, the leak
rate drops rapidly as helium is quickly evacuated from the leak detector by the
actions of the high vacuum and mechanical pumps. The end result is a rise and fall of
the leak rate indication on the display, which is directly proportional to the leak rate
in the test object.
Table 1-3
OPTO–22 Module Part Numbers
Vacuum Technologies
Part No.
Mfr. Part No.
Description
L9018301
G4 IAC5
120 AC input module, quantity: 5 required
L9018302
G4 IDC5G
35 to 60 VDC input module, quantity: 5 required
L9018303
G4 IDC5D
2.5 to 28 VDC input module, quantity: 5 required
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