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Functional Description
Mass Spectrometer
Thermo Scientific
TSQ Quantum XLS Series User Guide
43
The turbomolecular pump is controlled by a Leybold TDS controller and powered by a
+24 V dc (250 W) power supply. The mass spectrometer circuit breaker switch and the
vacuum service switch, but not the electronics service switch, turn power for the
turbomolecular pump off and on. A fan draws air in from the front of the instrument to cool
the pump.
Power to the turbomolecular pump shuts off if the foreline pressure, as measured by the
Convectron™ gauge, is too high, or if the turbomolecular temperature is too high.
Forepump
An Edwards™ E2M30 forepump
(or roughing pump) establishes the vacuum necessary for the
proper operation of the turbomolecular pump. The forepump also evacuates the inlet valve
and the collision cell. The pump has a maximum displacement of 650 L/min and maintains a
minimum pressure of approximately 0.01 Torr (1 Pa).
The forepump is connected to the turbomolecular pump by a section of reinforced PVC
tubing. The power cord of the forepump is plugged into the outlet labeled
Forepump
on the
power panel (see
on
). This outlet supplies power to the pump and is
controlled by the main power circuit breaker switch and vacuum service switch, not by the
electronics service switch.
Convectron Gauges
A Convectron gauge measures the pressure in the inlet valve and the foreline, which connects
the turbomolecular pump and the forepump. A second Convectron gauge measures the
pressure of argon collision gas in the collision cell.
The Convectron gauge uses a Wheatstone bridge with a temperature dependent resistor to
measure pressure down to a fraction of a mTorr. The voltage present at the top of the bridge
depends on how fast the resistor can radiate heat, which is related to the pressure. The
pressure that the Convectron gauge measures is monitored by vacuum protection circuitry on
the Source PCB, which in turn is monitored by the embedded computer on the System
Control PCB. The vacuum protection circuitry detects whether the foreline pressure is too
high for the proper operation of the turbomolecular pump.
Ion Gauge
A Granville-Phillips™ 342 mini ion gauge measures the pressures in the analyzer region of the
vacuum manifold. 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.
CAUTION
Always plug the forepump power cord into the outlets labeled
Forepump
on the
right side power panel of the mass spectrometer. Never plug it directly into a wall outlet.
