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Cygnus 2 Operating Manual
2 Known, Used Crystal
The second category is for a “known, used” crystal, to account for the possibility
that a person would remove a good monitor crystal and then reinsert the same
crystal. Whenever a crystal fail occurs, the last valid crystal frequencies are
stored in Cygnus 2. Upon inserting a coated monitor crystal, the measured
frequencies for this crystal will fall outside of the allowed range for “new”
crystals. These frequencies are then compared with the stored values to
determine if this crystal is the same one as was in use prior to the crystal fail. If
the crystal is the same as used previously, and Auto-Z was being calculated
previously, Cygnus 2 will allow an Auto-Z calculation with this crystal.
3 Unknown, Used Crystal
The third category is for an “unknown, used” crystal. This category is for a used
crystal that, upon insertion, shows measured frequencies that are outside of the
allowed “new” crystal range and also do not match the frequencies stored
within Cygnus 2. This results in an “unable to Auto-Z” condition because the
initial frequencies of the uncoated monitor crystal are not known.
4 Unable to detect anharmonic frequency.
As mass is deposited onto the crystal, the oscillation is damped. This damping
may be severe enough that the resonance can no longer be determined. If
Cygnus 2 loses the ability to measure the first anharmonic frequency, but is still
able to determine the fundamental frequency, the “unable to Auto-Z” message
is displayed. Cygnus 2 will then continue to use the fundamental frequency to
monitor the deposition.
If Cygnus 2 loses the ability to measure the fundamental frequency and all
available crystals in a multi-position sensor head are flagged as failed, the
Crystal Fail message is displayed and the Xtal Fail logic state becomes true.
5 Unable to Auto-Z
An “unable to Auto-Z” condition occurs whenever:
The anharmonic frequency cannot be measured.
The fundamental and anharmonic frequencies of the monitor crystal have
not been continuously measured from the uncoated to the coated state.
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