HP 3468A - Calibration Procedures

One of the many features of the 3468A is electronic calibration. This represents a
totally new concept in Hewlett-Packard voltmeters. Before, voltmeters had to be
removed from their mounting, have their covers removed, and mechanical ad-
justments made. Then the voltmeter had to be reassembled and installed. But
now, calibration may be done by simply applying a stimulus and pressing a front
panel button. There is absolutely no disassembly required. It is beyond the scope
of this section to present the entire calibration procedure. For complete calibration
information refer to the 3468A Service Manual, -hp- part number 03468-90001.
Briefly, Electronic Calibration is done by applying a known voltage (or resistance or
current) to the voltmeter and telling it the exact value of that input. The voltmeter
then takes ten readings and compares the average of those readings to the known
value. A “CALIBRATION CONSTANT” is calculated to correct the reading to the
known value and then stored in the voltmeter’s memory. These Calibration Con-
stants are generated for each range and function of the meter. All subsequent
measurements are corrected by the constants. The Calibration Constant memory is
backed-up by a long life battery to maintain the constants when power is turned
off.
On
the
rear
panel
of
the
3468A
is
a
bank
of
eight
small
switches.
Switch
8
(right-
most)
is
the
CAL
ENABLE
switch
and
when
set
to
the
down
position
enables
the
3468A
to
be
calibrated.
A
‘’C:”
will
appear
between
the
numeric
field
and
the
alpha field in the display when calibration
is enabled. This switch should not be
set
except
when
qualified
service
trained
personnel
are
to
perform
the
calibration
procedures.
Enabling
the
CAL
switch
may
cause
loss
of
calibration
if
proper
pro-
cedures are not followed carefully.
|
Commands
C Calibrate
(see the 3468A Service Manual)
10