HP 6268B Operating And Service Manual

Figure 5-5. Load Transient Recovery Time Waveforms
5-31 Temperature Coefficient.
Definition: The change in output voltage per degree
Celsius change in the ambient temperature measured
while ac line voltage, output voltage setting, and load
resistance are all held constant.
5-32 The temperature coefficient of a power supply is
measured by placing the power supply in an oven and
varying it over any temperature span within its rating.
(Most HP power supplies are rated for operation from 0 C
to 55°C.) The power supply temperature must be allowed
to stabilize for a sufficient time at each measurement
temperature.
5-33 The temperature coefficient given in the specifi¬
cations is the maximum temperature-dependent output
voltage change which will result over any one-degree
interval. The digital voltmeter used to measure the supply's
output voltage change should be placed outside the oven
and should have a long-term stability adequate to insure
that its drift will not affect the overall measurement
accuracy.
5-34 To check the temperature coefficient, proceed
as follows:
a. Connect load resistance and digital voltmeter as
illustrated in Figure 5-1.
b. Turn CURRENT controls fully clockwise.
c. Turn on supply and adjust front panel VOLTAGE
controls until front panel voltmeter indicates maximum
rated output voltage.
d. Place power supply in temperature-controlled oven
(digital voltmeter remains outside oven). Set temperature
to 30 J C and allow 30-minute warm-up.
e. Record digital voltmeter reading.
f. Raise temperature to 40"’C and allow 30-minute
warm-up.
g. Observe digital voltmeter reading. Difference in
voltage reading between steps (e) and (g) should be less
than:
6259B, 6260B 12mV
6261 B 22m V
6268B, 6269B 42mV
5-35 Drift (Stability):
Definition: The change in output voltage for the first
eight hours following a 30-minute warm-up period. During
the interval of measurement, input line voltage, load resis¬
tance, and ambient temperature, are all held constant.
5-36 This measurement is made by monitoring the output
of the power supply on a digital voltmeter over the stated
measurement interval. A strip chart recorder can be used
to provide a permanent record. Place a thermometer near
the supply to verify that the ambient temperature remains
constant during the period of measurement. The supply
should be located away from any source of stray air currents.
If possible, place the supply in an oven and hold it at a
constant temperature. Take care that the measuring
instrument has an eight-hour stability at least an order of
magnitude better than the stability specification of the
power supply being tested. Typically, a supply will drift
less over the eight-hour measurement interval than during
the half-hour warm-up.
5-37 To check the output stability, proceed as follows:
a. Connect load resistance and dig ; tal voltmeter as
illustrated in Figure 5-1.
b. Turn CURRENT controls fully clockwise.
c. Turn on supply and adjust front panel VOLTAGE
controls until digital voltmeter indicates maximum rated
output voltage.
d. Allow 30-minute warm-up, then record digital
voltmeter reading.
e. After 8 hours, digital voltmeter reading should not
differ from the step (d) reading by more than:
6259B, 6260B 5mV
6261 B, 6268B 8mV
6269B 14mV
5-38 CONSTANT-CURRENT TESTS
5-39 The instruments, methods, and precautions for
the proper measurement of constant-current power supply
characteristics are for the most part identical to those
already described for the measurement of constant-voltage
characteristics. There are, however, two main differences:
5-6

HP 6268B Specifications

General

Brand	HP
Model	6268B
Category	Power Supply
Language	English