SRS Labs QMS 100 Series, User Manual

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Mass Filter Power Supply 2-7
Technical Reference
Mass Filter Power Supply
All the necessary electronics required to power up the quadrupole mass filter during mass measurements
are built into the ECU box. The RF/DC levels for each mass are set and regulated from the ECU, under
microprocessor control, and based on internal calibration parameters permanently stored in non-volatile
memory.
The difference between the three spectrometer models (100, 200 and 300) is given by the maximum
supply voltage available to the rods. For example, the maximum RF amplitude delivered to the probe in
the RGA300 is 1284 V (2568 Vpp) and corresponds to ions with mass of 300 amu (8.56Vpp/amu).
The corresponding DC potential is a maximum of about 430 VDC for masses of 300 amu (+215 Vdc
on one rod pair, and -215 Vdc on the other).
The frequency of operation of the mass filter is the same for all models and is fixed at 2.7648 MHz by
an internal clock.
The rod structures in the mass filter are primarily capacitive, so to reduce the circuit drive requirements,
the rod reactance is resonated with an inductance. The advantages of this resonant drive circuit is the
primary reason for operation at a fixed frequency.
The internal calibration parameters used by the microprocessor to set the RF/DC levels during scans
and measurements, are pre-programmed at the factory as part of the test and calibration procedures
performed on the instrument before shipping. However, the parameters can be readjusted easily and
whenever necessary using the Peak Tuning procedures described in the User’s Manual.