Stanford Research Systems RGA100, Operating Manual And Programming Reference

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4-2 Introduction
SRS Residual Gas Analyzer
Introduction
The SRS RGA is a mass spectrometer consisting of a quadrupole probe, and an
Electronics Control Unit (ECU). The ECU completely controls the operation of the RGA,
handles its data and transmits it to the computer for analysis and display.
Electronics Control
Unit (ECU)
Ionizer
Quadrupole Probe
Figure 1 Quadrupole Head Components
The ECU is a densely packed box of electronics (3”” x 4”” x 9””) that connects directly to
the probe’’s feedthru-flange and also to a host computer. It includes several regulated
power supplies, a built-in microprocessor, control firmware, and a standard RS232
communications port. It is powered by either an external 24VDC (@2.5Amps) power
supply or an optional, built-in power module which plugs directly into an AC outlet.
Warning
The ECU does not have any serviceable parts and does not require any routine
maintenance. All calibration procedures should be done using the RS232 interface
and the RGA calibration command set.
During normal operation of the RGA, regulated power supplies built into the ECU set the
electron emission current, the voltage levels on the ionizer electrodes, and the high
voltage across the electron multiplier. RF/DC levels for each mass are also set and
regulated by the ECU, based on internal mass calibration parameters permanently stored
in non-volatile memory. A built-in, logarithmic electrometer detects the ion currents
collected by the FC, or electron multiplier, and converts them to voltage signals that are
read by a built in A/D converter. The microprocessor automatically compares those
signal voltages against an internal calibration and calculates the magnitude of the ion
currents. The ion currents are then averaged as needed, offset corrected and transmitted to
the host computer over RS232 for immediate display.
Several built-in checks constantly monitor the operation of the probe and its operating
environment. For example, the filament emission, and the electron multiplier, are
immediately turned off in the case of accidental overpressure.
Active LED's on the rear panel of the ECU provide constant feedback on the status of the
filament, electron multiplier, electronics system, probe and communications, and alert the
user of any problems.