Veeco MS40 Operation And Maintenance Manual page 65

bouncing of the ions within the mass spectrometer). Therefore, a second
identical magnetic field is used again, which acts to virtually eliminate all ions
except for helium ions. By using this construction of two separate magnets
and baffles, helium is selectively transmitted to its target, while other gases,
even if present in large quantities, are rejected.
Ion Collector: After passing through the magnetic fields and baffles of the
spectrometer, the gas ions enter the ion collector. The ions strike a plate
known as the target. As the helium ion strikes the target, the target
becomes positively charged, causing an extremely small electron flow, as
low as 1 x 10
the collector. The first stage of amplification is within the high vacuum
environment to assure stability, minimize the time constant and reduce
stray "noise" pick-up. The amplified signal is proportional to the partial
pressure of helium within the source. This signal, the actual leak rate, is
sent to the MS-40 computer for display on the User Panel.
VALVE BLOCK ASSEMBLY
The valve block assembly consists of:
Note that the external rough valve, while part of the vacuum system, is not
located on the valve block.
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Amperes. The current flow is detected and amplified within
• Calibrator Valve (with Calibrator Assembly)
• Fine Valve
• Vent Valve
• Rough Valve
• Fore-line/Reverse Valve
• Gross Valve
• Sniffer Valve
• Purge Valve
• Test Port
• Test Port Pirani
• Vent Filter
• Purge Hose Connection
• Sniff Hose Connection
• Internal Mechanical Pump flex Line
• Fore-line "flex" Line
• Purge Sintered Filter
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