SRS QMS100* High Pressure Sampling Systems

Stanford Research Systems QMS series gas analysers 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 low 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 system 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 a variety of 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 turbo molecular/drag pump draws a small amount of gas through an aperture, which reduces the pressure to about E-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 rear-panel, 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 IBM compatible 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.

PPR100/200/300- 100 amu, 200 amu and 300 amu systems

• 0.01, 0.1, 1.0 or 10 Torr inlet pressure
• 3E-5 Torr-L/s flow rate
• 2 second response time (0.1 Torr)
• 100, 200 or 300 amu systems
• Field-replaceable electron multiplier and filament
• 6 orders of magnitude dynamic range
• RGA Windows software

SRS Process Monitoring Systems
The PPR Process Monitoring Systems are designed for inline process monitoring and diagnosis. Two paths are provided to the residual gas analyser (RGA): a high conductivity path for monitoring base vacuum, and a pressure reducing path for monitoring the process at operating pressure. The pressure reducing path contains a micro-hole orifice which is designed to operate at one of the following pressures: 0.01, 0.1, 1 or 10 Torr. It reduces the sample pressure to the operating pressure of the RGA (about E-6 Torr). This pressure drop is maintained by the pumping system which consists of a hybrid turbomolecular pump and a diaphragm pump. Both pumps are oil free and will not contaminate your process.

The inlet assembly that attaches to your process chamber is pictured above. The system includes an RGA, by-pass valve assembly and Tee, a controller, turbo pump, diaphragm pump, and Windows software program for data acquisition and control.

The software is used to operate the instrument in various modes, including analog scan, histogram mode, and pressure vs. time mode. Both Faraday cup and electron multiplier detectors are standard with the PPR system. The electron multiplier provides additional sensitivity and higher scan speeds. The PPR system is shipped completely assembled and calibrated, and is ready to attach to your vacuum process chamber.