INFICON IC/5 Thin Film Deposition Controller - Manual (Page 102)

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IC/5 Operating Manual
CRYSTAL QUALITY ’Q’ . . . . . . . . . 0 to 9
This parameter is used to ensure tight rate control by monitoring the information
obtained from the crystal. It can be used to effect a crystal fail when operating
in the single frequency mode. In the case of the dual sensor, Q only affects the
primary crystal. The “single frequency” mode is when the Z-ratio type is set for
Material Z, “dual frequency” mode is when the Z-ratio type is set for Auto Z.
For each sensor’s rate reading, the percent relative deviation from the sensor’s
rolling average rate is calculated. Each time this deviation is greater than the
allowed percent relative deviation, as determined by the Crystal Quality value,
a counter is incremented by one count. If the deviation is within tolerance, the
counter will count down. (The counter will not count below zero.) When the
count reaches 100, a crystal fail will be initiated. In this manner only sustained
erratic rate readings will trigger a crystal fail and instantaneous noise will be
ignored.
If Auto Z is in use, the crystal quality will trigger an Auto Z failure instead of a
crystal fail. This will change the instrument from dual frequency measurement
mode to single frequency measurement mode. For some materials, it is
possible to regain rate stability by this change. Once the switch to single
frequency has occurred and a waiting period has elapsed (four times the
Primary Time Constant plus the System Dead Time plus ten seconds), the
counter will again track the rate deviation. If the counter reaches 100 a second
time, a crystal fail will be triggered.
Table 4-3 Crystal Quality Number and Threshold of Rate Deviation
Crystal Quality
Number
Threshold of
Rate Deviation
9 2.5%
8 5.0%
7 7.5%
6 10.0%
5 12.5%
4 15.0%
3 20.0%
2 25.0%
1 30.0%
0 Disabled