SRS Labs QMS 100 Series, User Manual

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1–4 What’s Inside ?
SRS QMS Gas Analyzer
The system exhausts to the rear panel. All of the gas drawn into the inlet is exhausted through this port.
The port is a 1/4 inch Swagelok tube stub, which can be connected to a wide variety of tube fittings.
When sampling hazardous gases, the user must ensure that the exhaust gas is properly handled. The
pump behind the exhaust port cannot produce significant pressure above atmospheric; therefore,
provide a low resistance path when connecting extra exhaust tubing.
Three electrical connections are located on the back panel: a computer connection, power line, and
chassis ground. The computer is connected from its serial port to the 9 pin connector on the back
panel. The communications between the instrument and computer uses full hardware handshaking and
thereby requires all 9 wires in the cable. Beware that some 9 to 25 pin serial port adapters do not
contain all 9 connections. A standard three wire power cord is connected to the module on the back
panel. The module also contains the fuse(s). To replace the fuse, first remove the power cord. Next,
place a small screwdriver in the slot on the top of the module and pry open the cover. The red fuse tray
can then be accessed to replace the fuse. The ground stud is provided to meet CE requirements.
Operating Orientation
The QMS can be operated either standing or laid on its side. The instrument utilizes a pressure gauge
that will not operate correctly when the system is tipped front to back. The pumps contain
no oil or
other liquids and therefore gravity has no effect on them. If the system is to be laid on its side, the left
side (viewed from front) should be down. If the handle and rubber feet are removed, the system will fit
on a shelf in a standard 19” equipment rack. The system can be stored or transported in any
orientation.
What’s Inside ?
The instrument can be described in terms of two main subsystems: gas handling and mass spectrometer.
These two operate independently of each other. The gas handling subsystem draws in the sample gas
and transports it to the spectrometer at reduced pressure. The spectrometer analyzes the gas provided
to it. The spectrometer belongs to a specific class commonly referred to as
residual gas analyzer or
RGA. In this manual, we use RGA to refer to just the analyzer and QMS to refer to the entire
instrument. The following two sections provide a basic description of these subsystems, refer to the
Technical Reference Manual for a detailed description. For the curious, the Technical Reference
contains an internal photograph in Chapter 1.
Gas Handling Subsystem
Figure 1-3 shows a schematic of the gas handling system. The discussion in this manual assumes that
inlet gas is sampled at 1 bar using the standard capillary supplied with each instrument. The system
reduces the pressure of the gas approximately 9 decades from the inlet at 1000 mbar to 10
-6
mbar at
the RGA. This large reduction factor is accomplished in two stages. A flow of several milliliters per
minute (STP) is drawn into the capillary. The capillary bore diameter and length are such that the
pressure at the capillary exit is 1-4 mbar. The standard capillary has an inside diameter of 125
µ
m and