SRS Labs QMS 100 Series, User Manual

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Operation 1–11
SRS QMS Gas Analyzer
established, the sample valve will open, and measurements can be made. When the capillary flow valve
is first opened, a pressure pulse will occur in the system that will invariable shutoff the RGA filament. If
you where previously making measurements at state 2B, the RGA filament should be turned off while
starting the sample flow. Restart the RGA after the sample flow has been established.
An alternative route is to turn off the turbo pump and restart the system by the normal path
(0,1,2A,3,4). This avoids the valve pulsing discussed above and is slightly quicker. To use this path,
turn of the Turbo Pump switch and wait for the light to go off. Then (in this order) turn on the Capillary
Flow Valve, Turbo Pump, and Sample Inlet Valve. As with the previous method, turn off the RGA
filament during these steps.
Idle
When samples are not being measured, the system can be idled at two levels. Idle states minimize the
load on the pumps, thereby extending their life. The system also can pump out the background more
quickly at idle. These statements do not mean the system is not designed to operate continuously; the
system will run 24 hours a day.
For short periods, idle the system by closing the Sample Inlet Valve. This lowers the pressure in the
high vacuum area of the system and helps to keep the background minimized. Stopping the sample flow
when measurements are not being made is most important when gases containing water are being
measured. Water permeates into the walls of the vacuum chamber and is only removed slowly. The
less exposure to water, the quicker the background will be lowered.
For long periods, idle the system by closing both valves. With the capillary flow closed, the work load
of the diaphragm pump is at its lowest, which extends the life of the diaphragms. The turbo pump can
also more effectively pump the high vacuum area with both flows stopped.
Shutdown
The diaphragm pump should not be stored under vacuum for long periods. Because of this, different
procedures are recommended when the system is shutdown for short or long periods. For short
periods simply turn off the main power. For shutdown periods longer than about 30 minutes, it is
advisable to vent the system. There are several acceptable methods for venting. All are accomplished
by opening the Capillary Flow Valve with all the other switches off (state -1 on the diagram):
•
SLOW - While the turbo pump is still coasting to a stop, open the capillary flow valve with the
capillary still connected to the inlet. The system will be slowly vented, and the turbo will stop in
a few minutes. Once the pressure gauge shows atmospheric pressure, the system is vented.
•
FAST - Wait for the turbo pump to coast to a stop. Remove the capillary and open the
capillary flow valve. Useful when filling the system with a dry gas for storage.
•
FASTEST - When the turbo pump is still coasting to a stop, remove the capillary and open the
capillary flow valve. This instantly raises the system pressure to atmospheric. Unlike older
devices, the turbo pump will not be destroyed. Still, this is the least recommended path.
NOTE: Do not vent the system to pressures above atmospheric. If the capillary is
connected to a gas at pressures above 1 bar, monitor the pressure during venting. Stop
just as the pressure reaches atmospheric.