HP 3468A - Autozero Functionality

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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.
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