Continental Electronics 816R - Page 16

present. If the voltage from the RMS-to-dc
converter is not within the 4.95 - 5.05 V de
window, the circuit will then operate to make the
necessary corrections if switch SI is in the AUTO
position.
Assuming that switch SI is in the AUTO position,
if the filament voltage rises above +1 % of the
nominal value setting, the following actions are
taken. The output of the 5.05 V de comparator will
go low at U8-2 causing the output of U4 to go low
and DS4, the LOCK LED, will extinguish. Device
U8-11 will go high bringing the input of Ul-13
high. When either of the comparators goes low,
indicating a correction is necessary, U2B, U2D,
and U2C in combination act as an OR gate forcing
Ul-10 high which in turn triggers timer, U6. When
U6 is timing, the output pin 3 goes high
illuminating yellow LED DS1. At the same time,
Ul-3 output goes low which takes the input of U4-1
low. This output is fed through switch S1A to
inputs Ul-9, Ul-12 and U2-1 bringing them all
low. Hence, while the timer is in its timing state,
the outputs of U1C, U1D, and U2A are all high,
inhibiting the actuation of relays KI, K2, and K3
respectively. Once the timer U6 has timed out, the
inputs of U1C, U1D, and U2A fed from switch
SI A are brought high. At this point if the filament
voltage is still above the +1 % nominal value, both
inputs of U1 will be high, enabling actuation of
relay KI and the clutch assembly on the filament
voltage adjust variac motor. Simultaneously, both
inputs of U1D will go high forcing its output pin 11
to go low. The LOWER LED (DS2) will be
illuminated and relay K2 will be activated which in
turn actuates the lower winding in the motor
driving the filament voltage control variac. Once
the variac brings the filament voltage back inside
the range of nominal operation, the comparator
output of U8-2 will go high, and the above logic
actions are reversed removing power from the
filament voltage regulator variac motor.
The raise function operates just as the lower
function described above, but instead activates the
raise circuits. It may be noted that if future
adjustments by the operator are required in the
automatic mode, resistor A4R2 may be used as a
simple filament voltage adjustment control.
in the filament voltage. This delay timing period is
adjustable from 0 to 12 seconds with resistor R7.
If automatic operation of the filament voltage
regulator circuit is not desired, switch SI can be
put in the MAN (manual) position. This effectively
takes the regulator out of the circuit, but the green
LED lock indicator will still show if the filament
voltage is within nominal range.
While in the manual mode, momentary switches S2
and S3 can be used to manually activate the clutch
and raise or lower circuits respectively. Other than
the timer not being active in this mode, these
switches simulate the output of the comparators per
the operator's command, thus manually raising or
lowering the filament voltage. This provides a
convenient way to determine if most of the digital
logic and the solid state relay are functioning
properly should a problem occur. Devices U3A and
U3B are provided to insure that the raise and lower
functions are not activated simultaneously by circuit
failure or accidentally by the operator using the
manual control.
While in the manual mode, the operator may
depress both the raise and lower switches
simultaneously and the only action to take place is
the timing of U6 as noticed by the illumination of
yellow LED DS1. This allows the operator a
convenient way to set the time delay of U6 without
affecting the other circuits.
Solid state relays KI, K2 and K3 provide a return
for the ac voltages already on the windings of the
clutch, and the lower and raise circuits of the
variac drive motor. Relays K2 and K3 also have the
return path for the ac voltages routed through
micro-switches SI and S2 on the variac assembly.
This provides a secondary measure against
operating the filament voltage regulator outside of
the prescribed range provided by the mechanical
stops on the variac drive motor.
The filament voltage distribution is shown in Figure
8. Filament voltage regulator A2A4 maintains a
constant rms voltage on the filaments as discussed
above.
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The timing period of timer U6 is provided to guard
against constantly correcting momentary excursions