INFICON STM-2 USB Thin Film Rate/Thickness Monitor - Manual (Page 80)

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STM-2 Operating Manual
6.1.2 General STM-2 Troubleshooting
Table 6-2 General troubleshooting
SYMPTOM CAUSE REMEDY
Rate, Thickness, and Frequency
readings are unstable or
incorrect. Temperature of the crystal is
unstable (an AT-cut crystal may
drift as much as
10 Hz/°C). Control the vacuum chamber
temperature.
Move the crystal farther away
from the source (at least
25.4 cm (10 in.) from source).
Check sensor water cooling for
correct flow and temperature.
Refer to the sensor operating
manual.
Clean or replace the crystal
holder. Refer to the sensor
operating manual.
Use SPC-1157-G10 crystals
designed to minimize frequency
shifts due to thermal shock.
Humidity level on the crystal is
changing. Moisture being
absorbed or exuded from the
crystal surface. Avoid condensation by turning
off cooling water to sensor
before opening the vacuum
chamber to air. Flow water
above the dew point of the room
through the sensor when the
chamber is open.
Defective in-vacuum cable or
coax cables. Use an ohmmeter to check
electrical continuity and
isolation.
Crystal seating on the crystal
holder surface is scratched or
contaminated. Clean or replace crystal holder.
Refer to the sensor operating
manual.
Excessive cable length between
oscillator and crystal causes a
self-oscillation condition. Use no longer than a 78.1 cm
(30.75 in.) in-vacuum cable.
Use only the 15.2 cm (6 in.)
cable between STM-2 or
oscillator and feedthrough.