Status & Tuning Parameters
Analyser Tab
Thermo Fisher Scientific
Prima PRO & Sentinel PRO Mass Spectrometers User Guide
8-7
Note that it is detrimental to the gauge to leave it running for an
extended period (e.g. more than a few hours) while measuring
pressures greater than 10
-3
mbar. Excessive ion burns on the gauge
will occur, resulting in reduced gauge accuracy. This can only be
recovered by cleaning the gauge electrodes.
Ions are produced as a result of a discharge formed in the high
voltage field between the anode and cathode of the gauge head. As
the pressure in the system falls, the number of ions in the discharge
reduces and this can be directly associated with the pressure of the
chamber.
The analyser is protected from damage due to excess pressure by two
trip points based on the Penning gauge reading. The Penning gauge
gives a voltage output related to the pressure reading according to:
p = 10
U-10.5
Alternatively, the pressure / signal relationship can be expressed as
U = 10.5 + log
10
P
The high pressure trip (see
earlier in this
chapter) prevents operation of the emission circuit, ion energy,
multiplier, and source heater as described above.
A low pressure trip protects the same devices and is a level indicative
of a potential gauge failure.
The threshold values for these two trips are equivalent to:
High Pressure Trip = 3 x 10
-5
mbar (approximately)
Low Pressure Trip = 1 x 10
-7
mbar (approximately)
Hysteresis is built into the high pressure trip to allow for the pressure
rise that occurs when the filament begins to heat and outgas.
System Pressure Trip will indicate
OK
if the system pressure is
below the Pressure Set Point and
Fail
if the system pressure is above
the Pressure Set Point.
The Turbo Motor Current is the current drawn by the turbo
molecular pump motor.
The Turbo Operating Hours field indicates the running hours for the
turbo molecular pump. See the pump manufacturer’s
recommendations on service intervals.
Turbo Speed is the speed as a percentage of full speed of rotation.
100% is full speed.
System Pressure
Trip
Turbo Motor
Current
Turbo Operating
Hours
Turbo Speed
