HP 3468A - Page 15

With
autozero
turned
off,
whenever
a
new
function
or
range
is
selected
the
3468A
immediately
takes
one
final
zero
measurement
and
stores
the
results
in
its
internal
memory.
Subsequent
measurements
of
the
input
voltage
subtract
this
one
zero
measurement
to
correct
the
reading.
Since
only
the
input
voltage
is
measured,
the reading
rate almost
doubles.
AC
Voltage
and
Current
Since
the
input
signal
conditioning
circuitry
for
these
two
functions
is
ac-coupled,
it
is
not
necessary
to
correct
for
de
offsets
in
the
input
circuitry.
Thus
the
auto
zero
function
is
only
used
to
null
offsets
in
the
A/D
converter.
Turning
autozero
off
in
ac
volts
and
ac
current
eliminates
the
zero
reading
of
the
A/D
converter,
resulting
in a faster
reading
rate.
Resistance Measurements
For
2-wire
ohms
measurements
the
autozero
feature
performs
just
as
it
does
for
DC
voltage
measurements.
Resistance
measurements
using
the
4-wire
mode
re-
quire
different
considerations.
The
zero
measurement
is
normally
made
with
the
input
amplifier
shorted
to
circuit
common.
In
the
4-Wire
ohms
mode,
the
input
amplifier
is
shorted
to
the
4-Wire
SENSE
LO
terminal
for
the
zero
measurement.
With
autozero
“ON”,
the
zero
reading
is
updated
for
each
measurement
cycle.
With
autozero
“OFF”,
the
reading
is
not
updated
and
may
cause
an
ohms
measurement
error
if
the
resistance
of
the
test
leads
change.
To
prevent
this
error,
a
new
zero
reading
should
be
taken
by
changing
or
updating
the
state
of
the
3468A
anytime
test
leads
are
changed.
See
Also:
Display
(Integration
Time)
and
Optimizing
Reading
Rates
J | Commands
ZO Turns autozero off
Z1 Turns autozero on