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D. Primary/Transfer
Corona
Current and Grid Bias
Voltage Control System
1.
'Outline
The
circuit
shown
in Figure
3-23
controls the primary/transfer
coronil
current
and the bias
voltage
of the grid
of the
primary
corona.
M'ain functions
are as
follows.
a.
Switching
primary/transfer
corona
current ON/OFF
b.
Maintaining
primary/trahsfer
corona
currentconstant
c.
Switching
primary
corona
grid bias
voltage
d.
Switching
primary'
corona
grid bias
ON/OFF
In order
to eliminate
the effect
of
changes
in atmospheric
conditions
on the
effectiveness
of the corona
discharge,
the
current
to the
primary
corona
wire
is
maintained constant.
The
primary
corona
and
transfer
corona current are switched ON and OFF by
the HVT ON command (m).
The grid bias v&age
is switched by the
GRID ON signal (GRDON).
2.
a.
b.
3.
Switching
Primary/Transfer
Corona
Current
ON/OFF
When HVTON =
1
1.
Dlfferentlal amplifier goes OFF.
Lgo;s
OF/!
Variable
ulse width oscillator
LHfh-voltage
transformer
goes
0
F.
When HVTON = 0
1. Differential amplifier goes ON.
Variable pulse width oscillator
goes ON.
L
-
High voltage transformer
goes
ON.
Maintaining
Primary/Transfer
Corona
Current
Constant
If the primary corona current is greater
than the correct value due to changes in the
environment,
the level
(analog)
of the
feedback
signal to the differential
amplifier
circuit will increase and the output from the
differential
amplifier
circuit
will fall. As a
result, the primary/transfer
coronal
current
will fall. Similarly,
if the primary
corona
current is too low, it will be increased
If the output
side of the high-voltage
transformer
supplying
the primary
corona
assembly
should be overloaded,
the current
will be limited to a certain maximum.
3-25
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