b. ICs 5 and 6 are 4051B, one of eight switches. The output is determined by
the binary word input to channel or channels A SEL, B SEL, and C SEL. The input
channel binary words are A SEL = 1, B SEL = 2, and C SEL = 4. With the 100L-ma
station selected, the channel selected on ICs 5 and 6 is C SEL pin 9 which is a binary 4.
The output is pin 1 (4) which is high and potentiometers P5 and P15 are selected as the
ma-adjust pots. They are connected to the output, pin 3. Pin 3 of ICs 5 and 6 act as
inputs or outputs. In the case of IC5 it is an input, and for IC6 it is an output.
Accordingly pin 3 of IC6 will output some portion of negative (-) 8vdc as adjusted by P5
and P15 onto lead XDA, which is the ma set lead to the filament circuit. Internal to the
chip is a field-effect transistor (FET) switch from pin 1 to pin 3.
c. Pin 3 of IC5 inputs negative (-) 8vdc, which is output at pin 1 at the beginning
of an exposure, in effect shorting out P25 during the start of the exposure, giving the
filament an added boost at the start of the exposure. This added boost ensures the full
selected ma is across the tube from the first impulse of primary power through the last
impulse. The negative (-) 8vdc input to pin 3 of IC5 is supplied to pin 1 of IC5 via an
internal FET switch in IC5. Before an exposure is initiated, IC5 is inhibited due to OC1
optocoupler being turned off. Effectively, a high is at TP18 to pin 13 of IC4 producing a
high at pin 10 of IC4. This high goes to pin 6 of IC5 holding it off.
d. From the impulse-timer lead BAS is high throughout the actual length of
exposure turning on the OC1 optocoupler. This causes TP18 to be low and pins 13 and
10 of IC4 to be low, lifting the inhibit from IC5, and shorts out P25 during exposure.
When the exposure terminates, TP18 returns high inhibiting IC5. This sequence of
events takes place whenever a radiographic exposure is initiated.
e. A spot-film selection alters this sequence. For purposes of discussion,
assume the 200L SPOT, spot-film selection has been made. When this spot-film ma is
selected, a high exists on pin 13 of IC3 closing pins 1 to 2. This puts leads XDF fluoro
adjust and XDA ma-set together. Fluoro ma can now be adjusted via the fluoro-rate
control. As long as the cassette tray remains in the out-of-beam position, the
changeover switch will remain unchanged; pins 12 and 6 of IC3 will remain low so pins
10 to 11 and 8 to 9 will remain "open." Potentiometers P1, P11, and P21 are not
selected into the ma circuit.
(1) When a spot-film exposure is initiated due to the cassette tray moving
into the field, FE/RL are closed, energizing relay Re-5-SF and opening the normally
closed contacts XAS1/XAF and closing the normally open contacts XAS1/XA1. Pin 13
of IC3 returns low, opening pins 1 to 2 and removing XDF fluoro adjust from the XDA