2-13. ROTOR CONTROL CIRCUIT (CIRCUIT FUNCTION DESCRIPTION 7.0)
Refer to figure 2-11. Both X-ray tubes: over-table and under-table, are controlled
by this controller. The controller starts the anode of the X-ray tube spinning, reduces
the voltage across the stator winding of the X-ray tube after a pre-set period of time,
maintains a sensing circuit for monitoring the voltage and current of the phase shift
capacitor, and removes the stator voltage at the end of the exposure.
a. A jumper wire between leads HF and FE make the provision for continuous
rotation of the under-table tube possible. If continuous rotation is not desired, then
jumper across HF and H3. It is highly recommended to have continuous rotation on the
under-table tube whenever it is in use.
b. The Re-4 tube-select four-pole, double-throw (4PDT) relay is used to connect
either the over-table or under-table X-ray tube to the rotor controller. This relay is
operated via lead FE. When lead FE is 115vac, the relay is energized and the
under-table tube is selected. If lead FE is low, then the over-table tube is selected.
c. The operation of the rotor control is initiated by depressing the PREPARE
push button in radiography and by depressing the footswitch in the fluoro mode. For
this discussion, assume the over-table tube is in use and the PREPARE push button is
depressed for a radiographic exposure.
d. From the exposure circuit via the PREPARE push button is 115vac on lead
H3 which branches into two circuits. One circuit is to a set of normally closed contacts
on the 4PDT relay Re-3 which is energized when the rotor reaches speed and
illuminates the "GO" LED.
e. The other circuit for lead H3 is through a set of normally closed contacts on
the tube-select relay Re-4 to the common pin of contact GT1 and GT2 on relay
Re-2-RC and also is rectified, filtered, and zenered to become the positive (+) 24vdc
source. This 24vdc source turns on transistor Q2 which allows Re-2-RC to energize,
closing contacts H3/GT1 and the remaining three sets of normally open contacts close
to short circuit the sensors during boost time.
f. Across the boost-time-adjust potentiometer P1 and its series resistors is
24vdc and it is across a 15-M Ohm resistor in series with the 0.1-μFd timing capacitor.
Potentiometer P1 sets the trip point and turns on SCR2 (silicon-controlled rectifier) to
change from a boost cycle to a RUN cycle.
g. During the boost cycle and while the timing capacitor is charging, 115vac is
across the closed contacts H3/GT1 to the GT1 triac and causes it to conduct. From
lead H2F comes 230vac through the GT1 triac to the closed contacts Re-4 H7/O7.