INFICON STM-2XM 2-Channel Rate/Thickness Monitor - Manual (Page 125)

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STM-2XM Operating Manual
Rate, Thickness, and Frequency
readings are noisy. Excessive cable length between
oscillator and crystal. Use 78.1 cm (30.75 in.)
in-vacuum cable (or shorter).
Use 15.2 cm (6 in.) cable
between oscillator and
feedthrough.
Electrical noise is being picked
up by the coax cable between
the oscillator and STM-2XM. Locating the coax cable(s) at
least 30.5 cm (1 ft.) away from
high voltage / high power cables
and other sources of electrical
noise significantly reduces noise
pickup.
Inadequate system grounding. Ground wires or straps should
connect to an appropriate earth
ground.
Ground wires or straps should
be short with large surface area
to minimize impedance to
ground (refer to
section 2.1.2 on
page 2-2 ).
Thickness reading has large
excursions during deposition. Mode hopping due to damaged
or heavily dampened crystal. Replace the crystal.
Crystal is near the end of its life. Replace the crystal.
Scratches or foreign particles on
the crystal holder seating
surface. Clean the crystal seating surface
inside the crystal holder or
replace crystal holder. Refer to
the sensor operating manual.
Uneven coating onto crystal. A straight line from center of
source to center of crystal
should be perpendicular to face
of crystal.
Particles on crystal. Replace crystal.
Remove source of particles.
Intermittent cables or
connections. Use an ohmmeter to check
electrical continuity / isolation of
sensor head, feedthrough,
in-vacuum cable, and BNC
cables. Refer to the sensor
operating manual.
Inadequate cooling of crystal. Check water flow rate and
temperature for sensor cooling.
Refer to the sensor operating
manual.
Table 6-1 General troubleshooting (continued)
SYMPTOM CAUSE REMEDY