118165-001 REV. A
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5.0
Predictive filament
The current level to be used during the preheat time for the coming exposure is decided as
follows (see fig 12):
1)
ADC values of the mA feedback current are sampled at the end of preheat just prior
to mA servo and stored in memory.
2)
At the end of the exposure the actual mA at the end of preheat is compared to the set
mA value and the difference calculated.
3)
If the error zero then the preheat is left unchanged, if the error is less than .25 mA the
preheat will be adjusted up or down by 1 LS-Bit (1.4 mA of filament current). If the
error is more then .25mA then the amount of adjustment is calculated by taking the
tube curve (delta filament current / delta mA for that delta filament current),
multiplying by the mA error and taking 80% of that value.
4)
If the exposure is terminated normally the preheat will be updated. If the exposure
terminated because of a fault, the preheat is left unchanged. In addition of the
exposure is less than 20msec long the preheat will not be updated, instead the value
for previous exposure will be used.
5)
If the value from the reading differs more than 0.5 A from the last value it will still
only be changed 0.5 A.
