ESI 250-DA - Generator Switch Operation; Power Switch and AC Amplifier Gain Control; AC Null Indicator Description

1.
CONTROLS
(cont.)
1.10
Generator
Switch:
The
switch
at
the
bottom
center
of
the
panel
chooses
the
generator
to
be
connected,
to
the
bridge*
In
the
internal
ac
position
the
output
of
the
internal
generator
is
connected
to
the
bridge
generator
corners.
In
the
external
generator
position
the
bridge
corners
are
connected
to
the
external
generator
terminals.
In
the
internal dc
position
the
internal
dc
generator
is
connected
to
the
bridge
generator
corners
.
1.11
Galvanometer:
The
meter
in
the
center
of
the
panel
is a
sensitive
gaiygLnometer
which
is
used
for
indicating
a
bridge
balance.
The
two
mounting
screws
are
connected
to
the
galvanometer
terminals
so that
it
may
be
easily
connected
to
other
external
circuits.
The
large
knob
on
the
galvanometer
can
be
rotated
for
mechanically
positioning
the
galvanometer
pointer.
When
the
lock
button
is
pushed
in
the
direction
of
the
arrow,
the
galvanometer
suspension
is
rigidly
supported
for
protection
during
transportation.
1.12
Power
Switch
and
AC
Amplifier
Gain:
The
left-hand
control
knob
on
the
small
upper
panel
controls
the
AC
detector
sensitivity.
The
power
switch
for
the
unit
is
connected
to
the
same
knob.
The
adjacent
pilot
light
indicates
when
power
is
supplied
to
the
bridge.
1.13
AC
-
DC
Switch
and
AC
Generator
Gain;
The
right-hand
control
knob
on
the
small
upper
panel
controls
the
ac
generator
output.
In
the
extreme
counter-clockwise
position,
it
switches
the
ac
generator
off
and
the
dc
generator
on.
1.14
DC
Generator
Voltage
Switch:
The
switch
on the
right-hand
side of
the
small
panel
provides
for
high
and
low
values
of dc
voltage^
for
resistance
measurements.
The
low
value
gives
greater
sensitivity
for
unknown
resistors
below
about
100
ohms,
and
the
high
position
gives
greater
sensitivity
above
about
100
ohms*
This
switch
has
no
effect
on
the
ac
generator.
1.15
AC
Generator
Tuning
Network:
The
upper
right-hand
plug-in
unit
controls
the
frequency
of
the
oscillator.
1.16
AC
Detector
Tuning
Network:
The
upper
left-hand
plug-in
unit
determines
the
frequency
response
of
the
detector.
With
this
network,
the
detector
has a
narrow
acceptance
band
centered
at
the
generator
frequency.
With
this
network
removed,
the
detector
has a
flat
response.
1.17
AC
Null
Indicator:
The
electron-
ray-tube
visual
null
indicator
provides
high
sensitivity
and
rapid
response.
A
null
is
indicated
by the
maximum
opening
of
the
eye
.
1.18
AC
Amplifier
Output
Terminals:
The
two
terminals
at
the
top
of the
small
panel
are
for
connecting
an
oscilloscope
or
other
indicator
to
the
output
of
the
detector
amplifier.
They
are
in
parallel
with
the
visual
null
indicator.
The
black
terminal
on
the
left
is
connected
to
the
bridge
chassis.
The
red
terminal
on
the
right
is
connected
through
a
capacitoi
to
the
detector
output.
lelsin
250-DA
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