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INSTRUCTION MANUAL
Digital
MultImeter
Models
172A.
i73A
THEORY OF OPERATION
Overall
Operation.
Signal
routing
in
the
signal
conditioning
circuitry
is essen-
tidily
as shown
in
the
simplified
block
diagram
(Figure
5-Z).
Front
panel
switching
selects
the
applicable
path
for
the
input
signal.
For example,
an ac current
input
would
be routed
through
switch
"A"
to
the
I/V
converter.
The ac voltage
output
from
the
I/V
converter
would
be routed
through
the
"Q"
switch
and the
"DC/AC"
switch
to
the
AC/DC
converter,
and the
dc voltage
output
of
this
circuit
would
then
be routed
to
the
AD
converter
through
the
clamp
and active
filter.
The required
switching
and signal
conditioning
for
an ohms or voltage
input
can also
be readily
determined
from
the
diagram,
and
is
left
to
the
user.
The front
panel
switching
and signal
conditioning
circuits
will
be described
in greater
detail
in the
following
paragraphs.
b.
Switching.
Front
panel
pushbutton
switches
control
power,
function
and ranging
for
the
Model
lJ2A/lJ3A.
A summary
of
the
switching
is
given
in Table
5-l.
Additional
information
on function
selection
and
range
selection
switching
is
given
in Paragraphs
5-3i
and 3j,
respectively.
SWITCH
LINE
LINE
BAT
BAT
AUTO/MAN
AUTO/MAN
DN Range
UP Range
STYLE
TABLE
5-l .
Summary of
Pushbutton
Switching.
Push-Push
Push-Push
Push-Push
Push-Push
Push-Push
Push-Push
Momentarv
Momentary
SETTING
In
(On)
Out
(Off)
In
(On)
Out
(Off)
In
Out
In
In
REMARKS
DHM is powered
by ac line
power.
Battery
pack
(if
installed)
has a trickle
charge.
DMM is
disconnected
from
line
power.
Batter
pack
(if
installed)
is charged
at
maximum
rate
if
line
cord
is connected
to power.
DMM is
powered
by internal
Battery
Pack.
DMM is disconnected
from
Battery
Pack.
NOTE
Interlock
prevents
both
LINE and BAT
Push-
buttons
IN at
the
same time.
Both
push-
buttons
musr
be set
to OUT before
either
can be set
to
IN.
Push-Push
means
that
a
single
depression
will
place
the
pushbutton
to
IN,
a second
depression
will
release
the
pushbutton
to OUT.
DMM is
set
to MAN (Manual
Mode).
To change
range,
depress
either
DN RANGE or UP RANGE.
See also
REMOTE PROGRAMMING OPTION.
DMM is
set
to AUTO (Automatic
Ranging
Mode.)
DMM range
is
set
automatically.
Momentary
depression
causes
the
DMH to down
range
one decade
to greater
sensitivity.
Operable
only
when AUTO/MAN is
IN.
Momentary
depression
causes
the
DMM to up
range
one decade
to
lesser
sensitivity.
Operable
only
when AUTO/MAN is
IN.
5-3
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