HP 6268B Operating And Service Manual

First, the power supply performance will be checked
between short circuit and full load rather than open circuit
and full load. Second, a current monitoring resistor is
inserted between the output of the power supply and the
load.
5-40 For all output current measurements, the current
sampling resistor must be connected as a four-terminal
device in the same manner as a meter shunt would be. The
load current is fed to the extremes of the wire leading to
the resistor while the sampling terminals are located as
close as possible to the resistance element itself (see Figure
5-6). A current sampling resistor should have low noise,
low temperature coefficient (less than 30ppm/°C) and
should be used at no more than 5% of its rated power so
that its temperature rise will be minimized.
NOTE
In case of difficulty obtaining a low resis¬
tance, high current resistor suitable for
current sampling, a duplicate of the
sampling resistor used in this unit (A4R123,
or A4R123A and A4RI23B) may be
obtained from the factory.
5-41 Current Output and Ammeter Accuracy. To check
that the supply will furnish its rated output current, pro¬
ceed as follows:
a. Connect test setup shown in Figure 5-7.
b. Turn VOLTAGE controls fully clockwise.
c. Turn on supply and adjust CURRENT controls
until front panel ammeter indicates maximum rated
output current.
d. Digital voltmeter should read 0.5 ±0.01 Vdc.
5-42 Load Effect (Load Regulation}.
Definition: The change AIqjjj in the static value of
the dc output current resulting from a change in load
resistance from short circuit to a value which yields
maximum rated output voltage, or vice versa.
Figure 5-6. Current Sampling Resistor Connections
5-43 To check the constant-current load effect proceed
as follows:
a. Connect test setup shown in Figure 5-7.
b. Turn VOLTAGE controls fully clockwise.
c. Turn on supply and adjust CURRENT controls until
front panel ammeter indicates exactly maximum rated
output current.
d. Read and record voltage indicated on digital voltmeter.
e. Short circuit load resistor (R^).
f. Digital voltmeter reading should not differ from
reading recorded in step (d) by more than:
6259B 110/A/
6260B 110/A/
6261B 110/jV
6268B 134//V
6269B 120/iV
5-44 Source Effect (Line Regulation).
Definition: The change AIq^j in the static value of dc
output current resulting from a change in ac input voltage
over the specified range from low line to high line or from
high line to low line.
5-45 To check source effect, proceed as follows:
a. Connect test setup shown in Figure 5-7,
b. Connect variable autotransformer between input
power source and power supply ac input.
c. Adjust autotransformer for 208Vac input.
d. Turn VOLTAGE controls fully clockwise.
e. Turn on supply and adjust CURRENT controls until
front panel ammeter reads exactly maximum rated output
current.
f. Read and record voltage indicated on digital voltmeter.
g. Adjust autotransformer for 254Vac input.
h. Digital voltmeter reading should not differ from
reading recorded in step (f) by more than:
6259B IIOpV
6260B 110/iV
6261B IIOpV
6268B 134/jV
6269B 120pV
5-46 PARD (Ripple and Noise).
Definition: The residual ac current superimposed on
the dc output of a regulated power supply. Ripple and
noise measurements may be made at any input ac line,
voltage combined with any dc output voltage and load
current within the supply's rating.
5-47 Most of the instructions pertaining to the ground
loop and pickup problems associated with constant-voltage
ripple and noise measurement also apply to the measure¬
ment of constant-current ripple and noise. Figure 5-8
illustrates the most important precautions to be observed
when measuring the ripple and noise of a constant-current
5-7

HP 6268B Specifications

General

Brand	HP
Model	6268B
Category	Power Supply
Language	English