INFICON RSH-600 Rotary Sensor - Manual (Page 26)

3 - 4
IPN
1
5
3800
-G
RSH-600 Operating Manual
3.3 Maintain the Temperature of the Crystal
Periodically, measure the water flow rate through the crystal sensor to verify that it
meets or exceeds the value specified in
section 2.5 on page 2-5 . 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 supply taps that provide high total flows. An obstruction
or closed valve in the pipe that supplies water to the sensor head would not result
in a noticeable reduction of total flow. The best test is to directly monitor the flow
leaving 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.
3.4 Use the Optimum Crystal Type
Certain materials, especially dielectrics, may not adhere strongly to the crystal
surface and may cause erratic readings. For many dielectrics, adhesion is
improved by using crystals with alloy coated electrodes. Gold is preferred for other
applications.
3.5 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 material is observed, replace the crystal.
3.6 Crystal Holder Maintenance
In many applications, the surface where the crystal contacts the crystal holder may
require periodic cleaning. Material buildup on this surface can cause erratic or poor
electrical contact between the crystal and the sensor body. This buildup can also
cause a reduction in thermal transfer from the crystal to the sensor body. Both of
these can result in excessive rate noise or premature or intermittent crystal failure.
Cleaning may be accomplished by gently buffing the crystal holder to crystal
seating surface with a white Scotch-Brite™ pad followed by an ultrasonic bath in
soap solution followed by thorough rinsing in deionized water and drying or by
ultrasonic cleaning and rinsing only.