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Maintenance
Figure 5-2: Setting the value of the setpoint.
With the Alicat set to 00.0 mmHg, and all the inlet valves closed, the gas cell and system MGS
should now experience maximum vacuum. The pressure reading should drop significantly;
depending on the strength of the vacuum, the pressure will likely be between 20 – 125 ppm.
6. When the pressure has dropped, close the FTIR OUTLET RESTRICT Swagelok valve to block
the vacuum from the gas cell. The Alicat reading may bounce slightly when the vacuum is blocked
but should stabilize quickly.
7. If the gas cell/MGS fittings are all properly tightened, the pressure value should stay constant,
with a leak rate < 1 torr/minute. Typically, you will see much faster changes in pressure if there is
a leak somewhere in the system.
a. If the pressure changes significantly, check the fittings/connections on the rear panel to verify
a tight fit and test again.
Note Adjust the fittings to be finger-tight, then tighten nut 1-1/4 turns of the fitting with a
wrench. Do not overtighten.
b. If the Alicat pressure reading stays constant or indicates only a slow leak, then the MGS
fittings are connected properly.
8. Reset the Alicat SETPT values from 00.0mmHg back to 650.0 mmHg and turn the OPEN
SAMPLE valve to bring the gas cell pressure back to the 650 mmHg target value.
60 Modular Gas System User Guide Thermo Scientific