SRS Labs QMS 100 Series, Руководство пользователя

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1-4 Overall System
SRS QMS Gas Analyzer
The pressure gauge operates on 15 VDC, which is provided by the microcontroller. The gauge has on-
board electronics that provide a setpoint comparison. The setpoint check is used by the microcontroller
to determine if the system is operating acceptably. The gauge also outputs an analog signal related to
the pressure. This signal is displayed on the front panel. The output of the gauge is not linear, and
thereby the spacing of the numbers on the display is irregular. The front panel display is too coarse to
be used analytically.
Structure
The QMS is built with a thin aesthetic skin surrounding a structural steel chassis. Figure 1 shows the
instrument with the skin, bezel, and main side panel removed. (The Service chapter discusses dis-
assembly.)
As seen in Figure 1, most of the components are attached to the left wall of the chassis (as viewed from
the front). Because of this, if the instrument is to be laid on its side, the left side is preferred; the weight
of the components is directly supported.
For mounting the instrument, the feet and handle can be removed. The threaded inserts provide
convenient mounting locations. The handle holes accept 1/4-20 bolts and the feet accept 6-32 screws.
Note that the inserts only support tension; they will push-out if large thrust loads are applied. Do not
permanently hang the instrument from the handle mounts, support the weight from the bottom. There
are components behind the threaded inserts. Do not use screws that extend more than 1/2 inch into the
chassis.
Exhaust
The exhaust connection on the back panel is provided for handling hazardous gases. The connection is
a 1/4 inch Swagelok tube stub. The slight indent is intended to provide a perfect seal to other Swagelok
tube fittings. Use with other brand tube fittings cannot be recommended.
The exhaust can also be used to operate the QMS in a closed loop configuration, i.e . the exhaust
stream is returned to the supply. The closed loop operation is feasible because the QMS does not
significantly change the sample gas. The amount of the sample that is ionized by the mass spectrometer
is microscopic, less than 1 nanoliter per minute (STP). The ionizer produces a microscopic amount of
CO
2
, typically less than 50 nanoliters per minute (or 26 ml per year). No air leaks into the system and
no carrier or detector gases are added to the sample. Applications like glove box monitoring are well
suited to closed loop operation, because the instrument does not require a continuous bleed from the
box.