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QMS series gas analyzers offer an efficient, cost-effective solution
for a wide range of applications. These mass spectrometers simplify
the task of on-line process monitoring, analysis of gas species,
leak detection, and troubleshooting.
On-Line Monitoring
The QMS system can continuously sample gas at flow rates of several
milliliters per minute. The inlet can be equipped to sample at pressures
from 1 bar to 10 mbar. Data is acquired continuously, as opposed
to batch sampling which is employed by gas chromatographs.The QMS
has a fast response time of less than 0.5 seconds. Complete spectra
can be recorded in seconds, and individual masses can be measured
at rates up to 25 points per second.
Compact, User-Friendly Design
An advanced quadrupole mass spectrometer design, coupled with state-of-the-art
pumping technology, allows the entire system to be integrated in
a small, transportable package. The sampling inlet valves and pumps
can be controlled from the front panel. Operation is easy and does
not require a detailed understanding of the quadrupole or the pressure
reducing inlet. Since the pumps contain no oil or other liquids,
gravity has no effect on them which allows the unit to function
either standing upright or laid on its side. Capillaries are used
as sampling probes and are available in several materials and sizes
for different applications.
Principle of Operation
The QMS uses a two stage pressure reducing inlet to sample gases
at high pressure. This allows the use of a residual gas analyzer
(which operates at high vacuum) as the detector. Different capillaries
permit the system to sample at higher or lower pressures. A large
flow is drawn through the capillary which drops the pressure three
decades. A hybrid turbomolecular/drag pump draws a small amount
of gas through an aperture, which reduces the pressure to about
10-6 Torr, while most of the flow
is bypassed directly to a diaphragm pump. Solenoid valves control
the gas flow. The entire system is controlled by a microprocessor
which ensures correct operation of the pumps and valves. The software
manages the spectrometer and acquires data in a choice of six different
modes. An optional high-vacuum 2.75" CF port provides direct
access to the RGA.
Bypass Flow Configuration
The bypass flow stream and the sample flow stream are recombined
at the diaphragm pump, which makes it possible to use only one backing
pump. This contributes to the system’s small size. The bypass
flow configuration is also critical to the fast response time of
the QMS. Single-stage pressure reduction with leak valves would
lead to extremely small flow rates and unreasonably long sample
times. The bypass flow, on the other hand, gives a response time
of less than 0.5 seconds from the tip of the capillary to the RGA
chamber.
Windows Software
The QMS systems are supported with a Windows software
package that runs on PCs. The intuitive graphical user interface
allows measurements to be made quickly and easily. Data is captured
and displayed in real-time or scheduled for acquisition at specified
time intervals. Features include analog and histogram scan modes,
pressure vs. time plots, leak detection, annunciator mode, gas library,
audio and visual alarms, and comprehensive on-line help. Probe parameters
can also be controlled and monitored through a high-level ASCII
command set which allows easy integration into user control programs.
A standard RS-232 interface is used as the data link to the host
computer. A LabVIEW
driver is also available onthe SRS website.
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