mA Generation
Failure Possible Cause Remedy
Wrong
filament
current
observed
(when voltage
correct)
If filament current is wrong,
mA generated may be
wrong. Incorrect filament
selected, changing gain of
current sensor. Faulty
filament current sense
resistor. Filament regulator
faults. Tube aging.
Filament current is monitored by a true rms sensing circuit on the Generator
Driver PCB. The circuit sends an analog signal FIL_CUR to the X-Ray Controller
PCB. This signal is monitored by software to verify that the filament current is in
the expected range for the selected filament and technique, before the shot is
initiated. Filament voltage FIL_VOLT is similarly monitored. A signal
SM_FIL_ACK* is also generated by the filament selection relay so that the relay
operation can be verified by software. Filament B+ is monitored by software via
FIL_B_SEN and should be in the correct range of either about 160V or about
140V, depending on the filament selected. Inverter B+ is also monitored via
INV_B_SEN, and is checked to verify its presence at the Filament Driver, and that
the battery voltage is in its proper operational range. Further mitigation is
provided by mA correction during the shot. If aging results in the wrong filament
current, mitigation is provided by logging the gradual change in filament
characteristics since the last calibration.
Filament
current error
If filament current is wrong,
then mA could be wrong.
Filament aging, wrong
filament selected, broken
connection, current sense
gain wrong.
Assuming that the filament voltage is correct, a wrong filament current reading
could be caused by filament aging, wrong filament selection, wrong filament
current sensing gain, other faults on the filament current sense circuit, errors at
the X-Ray Controller PCB, or disconnections of interconnecting cables. Software
monitors the effects of aging to determine if a gradual change is occurring. In any
case, the ABS system will compensate for this effect. If the wrong filament is
selected, the SM_FIL_ACK* signal is monitored to determine correct operation of
the relay. Incorrect gain could be caused by failure of a relay contact, but this is
very unlikely. A disconnection would probably result in failure to monitor the
current. If the mA sensor on the HV Supply Regulator is working, software might
determine that X-ray production could continue without accurate verification of
filament current, since the ABS system would tend to correct any mA error.
11
Service
Periodic Maintenance
Contents
Schematics
Illustrated Parts
Installation
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