HP 3457A - Page 206

u1oL
INPUT HYBRID
6
apc
To vmio1
$4520 F.12,23
Figure 8-6. Front-End Offset Circuitry
Test
5
checks
the
current
source,
gain
select
and
input
divider
circuitry
on
assembly
A2/1.
The
Main
Controller
(ALUS5OL)
initially
configures
the
measurement
section
for
3
volts
DC,
10
power
line
cycles
integration
time
with
the
fixed
input
impedance
on.
The
configuration
is
changed
to
the
30V
and
300V
ranges
for
later
stages
of
the
test.
The test consists of applying the 100nA ohms current source to the DCV front-end which is set for
10M
ohm
input
impedance
(FIXEDZ
ON).
A/D
Controller,
A2U101
sets
the
ohms
current
source
to
100nA
and
closes
K201.
This
applies
the
100nA
to
the
10M
ohm
input
impedance
at
UIO1
pin
|
through
K107
thus
yielding
approximately
|
volt
as
an
effective
input
to
the
DCV
front-end.
This
|
volt is first measured on the 3V range at UI01I pin 13. Next the 30V range is selected which changes
the
input
amplifier
gain
and
turns
on
UIO!
switch
5
which
provides
a
lower
level
signal
to
the
input
ampli After the 30V range is measured, the 300V range is selected. This changes the input
amplifier
gain
and
another
measurement
is
taken.
Figure
8-7
illustrates
some
of
the
circuitry
used
for
this test.
The results are sent to the Main Controller for error checking. If a failure is detected and the
AUXERR? command is executed, the number 32 will be displayed on the control panel if their are no
other errors (See Table 8-2).
HP 3457A Multimeter
8-41