Functional Description
MS Detector
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______________________ Finnigan LTQ Hardware Manual _______________________
The forepump is connected to the turbomolecular pump by a section of 3.8 cm
(1.5 in.) ID reinforced PVC tubing. The power cord of the forepump is
plugged into the outlet labeled Mech. Pumps on the power panel (See
Figure 2-6 on page 2-10). This outlet supplies power to the pump and is
controlled by the main power circuit breaker switch and not by the electronics
service switch.
Convectron Gauge
The Convectron gauge measures the pressure in the ion transfer
capillary-skimmer region of the vacuum manifold and the foreline, which
connects the turbomolecular pump and the forepump. The pressure measured
by the Convectron gauge is monitored by the Signal/Power Distribution PCB.
The Signal/Power Distribution PCB detects whether the foreline pressure is
too high for the proper operation of the turbomolecular pump.
Ion Gauge
The pressure in the analyzer region of the vacuum manifold is measured by a
Granville-Phillips
®
342
mini ion gauge. The ion gauge produces energetic
electrons that cause the ionization of molecules in the ion gauge. Positive ions
formed in the ion gauge are attracted to a collector. The collector current is
related to the pressure in the vacuum manifold. The ion gauge is also involved
in vacuum protection.
Vent Valve
The vent valve allows the vacuum manifold to be vented to air that has been
filtered through a sintered nylon filter. The vent valve is a solenoid-operated
valve. The vent valve is closed when the solenoid is energized.
The vacuum manifold is vented when external power is removed from the MS
detector. (Power is removed from the MS detector by a power failure or by
placing the main power circuit breaker in the Off (O) position.) Power is
provided to the vent valve for 30 s after the external power is removed. If
external power is not restored to the MS detector in 30 s, power to the vent
valve solenoid is shut off. When power to the vent valve solenoid is shut off,
the vent valve opens and the manifold is vented to filtered air. The vent valve
closes after power is restored to the MS detector.
Caution. Always plug the forepump power cord into the outlet labeled
Mech. Pumps on the right side of the MS detector. Never plug it into a wall
outlet.