HP 3455A Operating And Service Manual page 67

Section V
Figure 5-2. 1 Volt Zero Adjustment.
k. Remove the top covers and note the value of
A1OR106 — if there is an R110 installed (see Figure 5-2).
Refer to Table 5-1 and record the Offset Voltage that cor-
responds to the current value of A1OR1 10: . (If there
is no A1OR110, record 0.000000 V.) If R110 is connected
to the terminal marked "+", the polarity of the Offset
Voltage is negative; if R110 is connected to the terminal
marked '"-", the polarity of the offset is positive.
1. Add the voltages recorded in Steps j and k to obtain
the total offset:
m. Refer to Table 5-! and locate the Offset Voltage
that is closest to the total offset voltage recorded in Step 1.
Obtain a resistor that corresponds to that offset voltage.
n. Remove the original A1OR110 (Figure 5-2). If the
total offset (Step 1) is positive, connect the new R110
between the unmarked terminal and the terminal marked
".": if the total offset is negative, connect it between the
unmarked terminal.and the terminal marked "+".
o. Reinstall the top covers and again allow the instru-
ment to run at room temperature for 30 minutes. At the
end of that period, the 3455A reading should be
0.000000 V + 4 counts. If it is not, repeat Steps j through
n,
Table 5-1. DC Zero Adjustment Padding List (A10R110).
Offset Resistor
Voltage Value* -hp- Part No.
0683-3055
0683-1555
0683-1055
0683-7545
0683-6245
0683-5145
0683-4345
0683-3645
0683-3345
0683-3045
*All resistors are + 5%, 1/4 W, carbon.
5-2
Model 3455A
5-12. DC AND OHMS REFERENCE ADJUSTMENTS.
5-13. The DC Transfer Standard required for the following
adjustments must be adjusted for optimum 1-volt and'
10-volt output accuracy using NBS-calibrated voltage
standards. The Transfer Standard should be adjusted just
prior to use. After adjustment, it should be left on and, if
possible, kept in a controlled environment where the
ambient temperature is within one or two degrees of the
temperature at which it was adjusted. The following pro-
cedure should be performed in that same environment.
5-14. Adjustment Procedure.
Equipment Required:
DC Transfer Standard (Fluke Model 731A)
Standard Resistor (1 kilohm + 0.0005%; .Guildline
9330/1 K)
Standard Resistor (100 kilohm + 0.002%; Guildline
9330/100 K)
NOTE
All of the reference adjustments are screw-
driver adjustments and are accessible through
holes in the rear panel of the Reference Module
{rear panel of instrument) Adjustment
Designators are marked on the panel The
adjustments should be performed after a 30-
minute warmup period with all covers installed.
a. Set the 3455A controls as follows:
FUNCTION seca 8 0G tie Gi Bars ease: ¢ DCV
RANGE. ois doe oat Pager eles a apes 10V
HIGH RESOLUTION. .............. ON
AUTO CAL ¢ uke sce py oki cowed ON
GUARD i. 25s. ete ceed heals ae Oe shows leave ON
TRIGGER (9 ge::5 0038 6 CR d wctnen Hd Bole INT
MATH cress cyetslod tyes had eieatie eet aeS OFF
b. Set the DC Transfer Standard for an output of 10 V.
Using short pieces of number 20 AWG (or larger) insulated
solid copper wire, connect the output of the Transfer Stan-
dard to the 3455A INPUT.
c. Adjust the 10 V pot for a 3455A reading of
+ 10.00000 V. :
d, Set the Transfer Standard for an output of 1 V. Set
the 3455A RANGE to 1 V.
e. Adjust the 10:1 pot for a 3455A reading of
1.000000 V (+ 1 count).
f. Set the 3455A RANGE to 10 V and set the Transfer
Standard for an output of 10 V.
g- Repeat Steps c through f until optimum adjustment
is obtained.