HP 740B Operating And Service Manual page 50

Model 740B
Section V
5-51. 1 V ADJUSTMENT (A10R10).
a. Set Model 740B controls as follows:
b. Connect a 1 kQ resistor across + and - OUT-
PUT terminals.
FUNCTION .
RANGE .
VOLTAGE SET.
SENSITIVITY.
INPUT . . . . .
·
.~VM
· . 1 V
. 00000
· X104
shorted
c. Depress OUTPUT pushbutton to apply 60 V
to load .
d. Turn A10R8 (MAX. CURRENT LIMIT) cw
until front panel OVERLOAD light glows.
b. Zero the meter with the front panel ZERO
control.
b. Zero the meter with the front panel ZERO
control.
d. Adjust A10R10 (METER 1 V ADJ. ) for a meter
deflection of - O. 9.
e. Turn A10R8 slowly ccw until OVERLOAD light
just goes out.
5-57. INTERNAL ALIGNMENT PROCEDURE.7
5- 58. The internal alignment procedure is a method of
accurately calibrating and adjusting the VOLTAGE
SET dividers, the Precision Range Divider and the
Reference Supply.
5- 59. The VOLTAGE SET resistors are ratio matched
with the front panel meter serving as the null indicator.
Meter ratio sensitivity is very high - - approximately
8 ppm full scale - - and a perfect null is both hard to
achieve and unnecessary. The adjustments should be
set as near null as possible and rechecked after the
procedure is completed. If null is maintained within
10% (one major meter division) of 0, the instrument
will operate well within its specifications. The first
adjustment, A1R1, calibrates a 2: 1 divider used as a
reference for the following adjustments. The next
eight adjustments (A1R2 through A1R9) match the
VOLTAGE SET resistors by adjusting the corresponding
parallel padding resistance on A1. After a long period
of time, one or more of the VOLTAGE SET resistors
may drift beyond the adjustment range of the variable
padding resistance. Paragraph 5-63 explains the pro-
cedure for modifying the padding resistance to com-
pensate for the long term drift.
5-62. The following steps describe the internal align-
ment procedure. The procedure is also outlined on
the instrument guard shield cover.
5-61. The last two adjustments of this procedure (A1R40
and A1R41) calibrate the internal reference supply.
An external reference voltage (-hp- Model 735A DC
Transfer Standard) and a null detector (-hp- Model
419A DC Null Voltmeter) are required for these ad-
justments.
5-60. A9RlO, A9Rll and A9R12 are adjusted to meter
indication values printed on the guard shield cover.
These values are determined at the factory for each
instrument and should not be changed unless the
precision divider (A9R4 through A9R9) is replaced.
If the precision divider is replaced, the new numbers
can be determined using the procedure given in Para-
graph 5-109.
•
~VM
· .1 V
.00000
X104
shorted
FUNCTION .
RANGE .
VOLTAGE SET
SENSITIVITY
INPUT . . . . .
a. Set Model 740B controls as follows:
FUNCTION. . . . STD
STD VERNIER . . . . . fully cw
c. DepressX1 SENSITIVITY and rotate X1 VOLT-
AGE SET to 9 (fully clockwise).
b. Adjust A10Rll (STD V,ERNIER ADJ.) for a
meter deflection of + 1. O.
5-55. MAXIMUM CURRENT LIMIT ADJUSTMENT
(AlOR8).
5-53. STANDARD VERNIER ADJUSTMENT (A10Rll).
5-54. The standard vernier adjustment adjusts the
voltage applied to the meter loop input in STD mode.
No external test equipment is required to perform this
adjustment.
d. Adjust A10R9 (METER 100 /lV ADJ.) for a
meter deflection of -1. O.
5-52. 100 /lV ADJUSTMENT (A10R9).
a. Set Model 740B controls as follows:
c. Rotate X103 VOLTAGE SET to 1 (one position
cw).
5- 56. The maximum current limit adjustment (A10R8)
sets the maximum available output current by adjust-
ing the range of the front panel CURRENT LIMIT con-
trol. A 1 kQ
±
5% 5 W resistor (-hp- Part No. 0812-
0099) is required for this adjustment procedure.
a. Set Model 740B controls as follows:
r
L
r
l 01794-1
RANGE .
FUNCTION .
VOLTAGE SET
STD VERNIER
CURRENT LIMIT
OUTPUT . . . . .
.100 V
STD
60.000
fully ccw
MAX
· . . off
a. Turn on the instrument and allow it to warm-
up for at least 60 minutes.
- - - - - N O T E - - - - -
In-tolerance instrument perfor-
mance can be expected when the
internal alignment procedure is
5-13