INFICON IC/5 Thin Film Deposition Controller - Manual (Page 261)

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IC/5 Operating Manual
during any one of these power increments then the rate transition for this
pre-determined power increment is used to calculate the control loop parameters.
There is no Rate control feedback during Quick Tune.
If a Complete Tune is chosen, a Quick Tune is done first and will proceed as
described above. These Quick Tune values are used as backup parameters in the
event a Complete Tune fails. After completing the Quick Tune, the instrument will
initially establish rate control to one-half the Desired Rate, then increment the
power level to obtain a rate at twice the Desired Rate.
If the Maximum Rate is exceeded, the power level will be adjusted to reestablish
rate control at one-half the desired rate and then increased to obtain a rate at the
Desired Rate. If the Maximum Rate is again exceeded, the instrument will leave
AutoTune and return the values calculated with Quick Tune. If the Maximum Rate
is not exceeded, the control loop parameters will be calculated based on the rate
transition. There is rate feedback when doing a Complete Tune.
The major difference in the implementation of AutoTune for a fast source (typically
an electron beam gun) as opposed to a slow source, is the way in which rate
stability is determined. For a fast source there can be many rate instabilities, such
as sweep frequency fluctuations and short term thermal shorts; therefore rate noise
makes determination of when the rate is stable impractical.
To circumvent this problem with a fast source the power level for both Quick Tune
and Complete Tune is increased to the appropriate level and held for approximately
9 seconds. The rate transition over this time period is used to calculate the Process
Gain parameter. Having calculated the Process Gain, the power level is returned
to the initial power setting (or rate if in Complete Tune) and the procedure is
repeated. The Process Gain value is again calculated and the two values
compared. If the relative deviation between the two values is less than 40%,
AutoTune for a fast source is completed.
This procedure may be repeated up to 4 times to obtain agreement between
calculated Process Gain values. If agreement can not be reached after four times,
Quick Tune values will be returned. A failure message will be returned if a Quick
Tune can not be accomplished. The time for a complete tune of a fast source is
typically no more than two minutes. A Quick Tune on a slow system typically takes
10 minutes, while a Complete Tune may take as long as 30 minutes.
12.6.4 Definition of AutoTune Messages
The following messages may appear while AutoTuning:
AutoTune Failure . . . . . . . . . . . . . . Inconsistent Quick Tune results are not
allowing control loop parameters to be
determined.
AutoTune Successful. . . . . . . . . . . The instrument has determined the system's
control loop parameters.