Fluke 93 Service Manual page 65

CIRCUIT
DESCRIPTIONS
3-31
The
configuration
depends
on
the settings of
switches
D2650 and
D2751. These
switches are
controlled
by
the signals
FILT
CALDC-
HD,
SQUAR
and
Si.
Table 3.8
lists
ttie
various settings
and
resulting generator output
signals.
Table
3.8 Generator
control signals
for
various generator output
signals.
STIMUL
CONTROL
SIGNALS
OUTPUT
SIGNAL
I
frequency duty
CALDC- RLT
SCXJAR
SI
amplitude
waveform
'
cycle
HD
1
488 Hz
50%
0
0
1 1
976 Mz
50%
0
0
1 1
Square wave
vonage
1.95
KKz
50%
0
0
1
1
-
1
0
0
1
3Vp-p
DC
voltage
976
Hz
50%
0
1 1
1
Vp-p
Sine
wave
voltage
20
kHz
0-100%
0
1
0
1 •2...+2VP-P
Slow ramp
voltage
20
kHz 0-100%
0
1
0
0
0...+3
mA
Slow ramp
current
In this
table
"V
means:
signal "high* (switch closed)
and *'0" means
signal "low* (switch
open).
The
slow
ramp
current signal
is
made
with
a current source.
A
simplified
schema^c diagram
is
given
in
figure 3.17;
Figure
3.17
Current
source
section of
generator
When
the duty cycle
of
STIMUL
Is0%, the
bridge
will
be
In
balance
and
current
1^
=
0.
When
the duty
cycle of
STIMUL
1$
increased, a
DC
component
is
generated, which has
a
linear relation to
the duty
cycle.
The
operational
amplifier
tries to
keep
the voltages
on
both inputs the
same.
The
operatbr>a{
amplifier
will
now
drive trana'stor
V2854
to
Increase
1^.
Because
Is
almost equal
to
the output
current
will
also Increase.
In this
way
it
is
possible to regulate the current
i^
by
means
of
the duty cycle
of
STIMUL.