HP 3457A Service Manual page 206

u1oL
INPUT HYBRID
6
apc
To vmio1
$4520 F.12,23
Figure 8-6. Front-End Offset Circuitry
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