INFICON UHV Bakeable Sensor - Manual (Page 36)

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UHV Bakeable Sensor Operating Manual
4.1.3 Maintain the Temperature of the Crystal
Periodically measure the water flow rate leaving the sensor to verify that
the flow rate meets or exceeds the flow rate value specified (refer to
page 1-7 ).
Depending upon the condition of the cooling water used, the addition of an in-line
water filtering cartridge system may be necessary to prevent flow obstructions.
Many system coaters use parallel water supplies that provide high water flow rates.
With a parallel water supply, an obstruction or closed valve in the pipe that supplies
water to the sensor head may not result in a noticeable reduction of total flow.
Therefore, monitor the flow leaving the sensor, not the flow entering the sensor.
The crystal requires sufficient water cooling to sustain proper operational and
temperature stability. Ideally, a constant heat load is balanced by a constant flow of
water at a constant temperature.
INFICON quartz crystals are designed to provide the best possible stability
under normal operating conditions.
No crystal can completely eliminate the effects of varying heat loads. Sources of
heat variation include radiated energy emanating from the evaporant source and
from substrate heaters.
NOTE: Water cooling temperature near the dew point in the room should be
avoided. Condensation can cause early crystal failures.
It is recommended that water cooling temperature be maintained at 5 to 10°C
above the dew point in the room during a vent of the system. Water cooling
temperature can be lowered to a temperature less than 30°C under vacuum.
4.1.4 Crystal Concerns when Opening the Chamber
Thick deposits of some materials, such as SiO, Si, and Ni will normally peel off the
crystal when it is exposed to air due to changes in film stress caused by gas
absorption. When peeling is observed, replace the crystal.