HP 6268B Operating And Service Manual

5. Since the impedance matching resistors constitute a
2-to-1 attenuator, the noise spikes observed on the oscillo¬
scope should be less than 2.5mV p-p instead of 5mV p-p.
5-26 The circuit of Figure 5-3 can also be used for
the norma! measurement of low frequency ripple. Simply
remove the four terminating resistors and the blocking
capacitors and substitute a higher gain vertical plug-in for
the wide-band plug-in required for spike measurements.
Notice that with these changes. Figure 5-3 becomes a
two-cable version of Figure 5-2B.
5-27 Load Transient Recovery Time.
Definition: The time "X" for output voltage recovery
to within "Y" millivolts of the nominal output voltage
following a "Z" amp step change in load current, where:
"Y" is specified as lOmV; the nominal output voltage is
defined as the dc level halfway between the static output
voltage before and after the imposed load change; and "Z"
is the specified load current change of 5 amps or the full¬
load current rating of the supply, whichever is less. Load
transient recovery time may be measured at any input line
voltage combined with any output voltage and load
current within rating.
5-28 Measurement Techniques. Care must be taken in
switching the load resistance on and off. A hand-operated
switch in series with the load is not adequate since the
resulting one-shot displays are difficult to observe on most
oscilloscopes and the arc energy occurring during switching
completely masks the display with a noise burst. Transistor
load switching devices are expensive if reasonably rapid
load current changes are to be achieved.
5-29 We suggest that a mercury-wetted relay connected
in the load switching circuit shown in Figure 5-4 be used
for loading and unloading the supply. When this load
switch is connected to a 60Hz ac input, the mercury-wetted
relay opens and closes 60 times per second. The 25k con¬
trol adjusts the duty cycle of the load current switching
to reduce jitter in the oscilloscope display. This relay may
also be used with a 50Hz ac input. The load resistance
shown in Figure 5-4 is the minimum resistance that can
be used without damaging the mercury-wetted relay contacts.
5-30 Measurement Procedure. To check the load
transient recovery time, proceed as follows:
a. Connect test setup shown in Figure 5-4.
b. Turn CURRENT controls fully clockwise.
c. Turn on supply and adjust VOLTAGE controls until
front panel ammeter indicates either 5 amps or the full-load
current rating of the supply, whichever is less.
d. Close line switch on repetitive load switch setup.
e. Set oscilloscope for internal sync and lock on either
the positive or negative load transient spike.
f. Set vertical input of oscilloscope for ac coupling so
that small dc level changes in power supply output voltage
will not cause display to shift.
g. Adjust the vertical centering on the scope so that the
tail ends of the no-load and full-load waveforms are sym¬
metrically displaced about the horizontal centerline of
the oscilloscope. This centerline now represents the
nominal output voltage defined in the specification.
h. Adjust the horizontal positioning control so that the
trace starts at a major graticule division. This point then
represents time zero.
i. Increase the sweep rate so that a single transient spike
can be examined in detail.
j. Adjust the sync controls separately for the positive
and negative-going transients so that not only the recovery
waveshape but also as much as possible of the rise time of
the transient is displayed.
k. Starting from the major graticule division representing
time zero, count to the right 50;jsec and vertically 1 OmV.
Recovery should be within these tolerances as illustrated
in Figure 5-5.
POWER SUPPLY
UNOER TEST
■ Yi
CONTACT PROTECTION
NETWORK
I 2,5uF 40 JJ 1 °^- 6W
' h ' (NOTE 3)
NOTE 2 I
REPETITIVE
ILOAO SWITCH (NOTE I)
OSCILLOSCOPE
NOTES
I. THIS DRAWING SHOWS A
SUGGESTED METHOD OF
BUILDING A LOAD SWITCH
HOWEVER .OTHER METHODS
COULD BE USED, SUCH AS
A TRANSISTOR SWITCHING
NETWORK. MAXIMUM LOAD
RATINGS OF LOAD SWITCH
ARE 5 AMPS, 500 V, 250W
[NOT 2500W)
2 USE MERCURY RELAY,
CLARE TYPE HPG 1002
OR W E TYPE 2766
3 USE WIREWOUND RESISTOR
MODEL R l I±5%)
6259B
6260B
6261 B
6268B
6269B
2ft 50W
2ft 50W
4ft I00W
8ft 200W
8ft 200W
Figure 5-4. Load Transient Recovery Time Test Setup
5-5

HP 6268B Specifications

General

Brand	HP
Model	6268B
Category	Power Supply
Language	English