2
Functional Description
Mass Spectrometer
Thermo Scientific
TSQ Quantum XLS and TSQ Quantum GC User Guide
45
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 milliTorr. 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 measured by the Convectron gauge 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 Gauges
A Granville-Phillips
®
342
™
mini ion gauge measures the pressures in the analyzer region of
the vacuum manifold and the Q0/ion source region. 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, located in the area of Q2, 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,
which is controlled by the Vent Delay PCB. When the solenoid is energized, the vent valve
closes. If the power fails or the main power circuit breaker is placed in the Off (O) position, a
4-farad capacitor located in the Power Entry Module keeps the solenoid in the closed position
for several minutes. If power is not restored in this time, then the solenoid opens and the
system is vented with filtered air. The vent valve closes after power is restored to the mass
spectrometer.
Collision Gas Flow Control Valves
The collision gas flow control valves control the flow of argon collision gas into and out of the
Q2 collision cell. A solenoid valve acts to shut off argon gas flow to the cell. The collision gas
pressure is regulated by a proportional valve that is controlled by the data system. You can set
the collision gas pressure (0 to 5 milliTorr) in the Define Scan dialog box of the EZ Tune
window.
Ions enter the Q2 collision cell, collide with the argon collision gas, and then, because of the
collision, dissociate into smaller fragments. See
“Collision Cell and CID Efficiency”
Argon enters the mass spectrometer through a 1/8 in. port on the left side of the mass
spectrometer.