118165-001 REV. A
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84
8.0
AEC (Automatic Exposure Control) Mode
In Standard AEC Mode the external AEC control input, also called
“Exposure Disable”, is allowed to gate the high voltage on and off. In order to
generate X-Rays Prep, Exposure Control and AEC must all be in the “ON” state,
which is High (Logic 1). In addition the unit must be in the ready state. When
running in AEC mode the exposure control timer only runs when the AEC signal
is high. The exposure sequence terminates when any of the following are true:
1.
Prep goes inactive (low)
2.
Exposure control goes inactive (low)
3.
The exposure timer times out. (Timer is set as part of exposure command)
4.
The 30 second Prep time is exceeded.
When in AEC Mode it is assumed that the AEC signal will be in the Off state
when the exposure sequence terminates. If the AEC signal is ON, an under-time
fault will occur. The rotor continues to run when the X-Ray is shut off by the AEC
signal. An example of AEC timing is show below for the case of Prep & Exposure
to HSS slow speed. Also note, in AEC mode Break After Exposure is
automatically disabled, and will not occur even if it is set. In addition the Break
after exposure hang time will be 30 seconds, regardless of the current setting.
Prep
Exposu
re
Ready
AEC
(X-Ray Disable)
X-Ray Enabled
X-Ray Disabled
HSS
STOP
BOOST
RUN
STOP
X-Ray On
Fig 16 - AEC Timing
