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3
The autozero key allows the user to selectively enable or disable the internal zero-
ing technique used in the 3468A.
Enabling autozero insures the user that any off-
set errors
generated
internal to the 3468A
are continuously
nulled
with
each
reading. This renders the most accuracy. There are, however,
many applications
where
disabling
the autozero
is advantageous.
With
autozero
off, the
internal
reading rate nearly doubles. This would be important in programmable applications
where speed is critical. Furthermore, the 3468A
input circuitry remains in a com-
pletely static state with autozero off. This is useful when making measurements in
extremely
high impedance
circuits where the internal switching transients
of the
3468A may affect the reading accuracy. Of course, any range or function change
that takes place with autozero off is automatically accompanied with an autozero
update. The thermal stability of the measurement environment is the most impor-
tant factor in deciding whether or not to turn autozero off. By simply keeping the
temperature
of the 3468A
at a fixed value, you can turn autozero
off without
adverse effects,
How
it A
Do This
Turn the 3468A off, then on again.
press:
Notice
that
the
display
is being
up-
dated
more
frequently,
indicating
a
faster
reading
rate.
Also
notice
that
the AZ OFF annunciator is now
on in
the display.
The
Autozero
feature
is
now
turned
off. Pressing the key se-
quence
again will turn
Autozero
back
on.
and Current
Autozero
is used
to
correct
for small
offsets
(thermal,
etc)
in the
DC
input
amplifier circuitry of the multimeter. With the Autozero feature enabled (Autozero
is enabled at power turn-on) the 3468A
takes two measurements
per reading: a
"zero"
measurement
and
a measurement
of the input voltage.
The
displayed
reading is the algebraic difference between
the two measurements.
The 3468A
makes
the zero
measurement
by disconnecting
the multimeter's
input terminals,
and then shorting the internal input circuitry to circuit common.
It then switches
back for an input voltage measurement.
All switching is internal and is automatic.
8
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