HP 740B Operating And Service Manual page 42

Model 740B Section V
a. Connecttest setup shown in Figure 5-3. Leave
the 20
n
resistor disconnected.
b. Set Model 740B controls as follows:
c. Using ZERO and STANDARD VERNIER con-
trols, make small changes in the 740B output
voltage until the null detector indicates null
on the 10 fJ.V range.
- - - - N O T E - - - - -
If
null cannot be reached, the
740B reference supply should
be adjusted even though the in-
strumentmaybe operating with-
in specifications. Paragraph
5-62 steps m through p gives
the procedure for adjusting the
reference supply.
5-22. This test measures noise and hum superimposed
on the 740B output. A sensitive dc voltmeter (-hp-
Model 419A DC Null Voltmeter) and a 1 Hz to 1 mHz
ac voltmeter (-hp- Model 403A AC Voltmeter)are
required for this test.
a. Set 740B controls as follows:
.STD
. 1 V
00000
o
. On
FUNCTION .
RANGE .
VOLTAGE SET .
STANDARD VERNIER.
DC OUTPUT .
where
Ro
=
output resistance in ohms.
6.E
=
change in output voltage, no
load to full load (null de-
tector reading).
6.1
=
change in output current, no
load to full load (0.05 A).
5-19. RADIO FREQUENCY INTERFERENCE (RFI).
5-20. If the Model 740B is to be checked for RFI in
accordance with MIL Spec. 6181D, connect the input
and output terminals as shown in Figure 5-4.
5-21. OUTPUT NOISE AND HUM TEST.
. . . STD
. . . . . . 1 V
0.99999
1.0 (fully cw)
MAX
. . . . . . On
FUNCTION .
RANGE .
VOLTAGE SET.
STD VERNIER .
CURRENT LIMIT.
OUTPUT . . . . .
d. Connect the 20
n
resistor across the 740B +
and - OUTPUT terminals.
e. The null detector reading should be
±
15 fJ.V
or less.
-----NOTE - - - - - -
1. An indication of 15 fJ.Vor less veri-
fies the load regulation specifi-
cation: less than (0. 0005%
+
10
fJ.V)
change, no-load to full-load.
b. Connect the dc voltmeter across the 740B +
and - OUTPUT terminals.
c. Zero the 740B output by adjusting ZERO con-
trol for a null indication on the voltmeter
(10 fJ.V range).
d. Voltmeter pointer movement (0. 01 Hz to 1 Hz
noise) should not exceed ± 1 fJ. V. This verifies
the 0.01 Hz to 1 Hz noise specification: less
than 1 ppm of range.
2. An indication of 15 fJ. V or less also
verifies an output resistance of
0.0003
n
or less, obtained from
the output resistance specification:
less then (0.0002 + 0.0001 Eout)
ohm sat dc. Output resistance can
be calculated from the formula:
6.E
R
o
=-xr
e.
In
a similar manner, check the 0.01 Hz to
1 Hz noise on the 10 V, 100 V and 1000 V
ranges. Table 5-3 lists the maximum volt-
meter pointer movement.
- - - - NOTE-----
Zero the 740B output each time
before the O. 01 to 1 Hz noise is
measured.
DC STANDARD/DIFFERENTIAL
VOLTMETER
hp
7408
@@@@@@0@
_--------.....f.~} (~.u_--------_
INPUT CABLE
hp
1I054A
OUTPUT CABLE
hp
1I055B
7408-8-0106A
Figure 5-4. RFI Test
01794-1
5-5