Transient Recovery Time Test Setup; Transient Recovery Time Waveforms - HP 6269B Operator’s, Organizational, Direct Support And General Support Maintenance Manua L

TM 11-6625-2958-14&P
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 action completely
masks the display with a noise burst. Transistor
load switching devices are expensive if reasonably
rapid load current changes are to be achieved.
5-30 A mercury-wetted relay, as connected in the
load switching circuit of Figure 5-5 should be used
for loading and unloading the supply. When this
load switch is connected to a 60Hz ac input, the
mercury-wetted relay will open and close 60 times
per second. Adjustment of the 25K control permits
adjustment of the duty cycle of the load current
switching and reduction in jitter of the oscilloscope
display.
5-31 The load resistances shown in Figure 5-5 are
the minimum resistances that must be used in order
to preserve the mercury-wetted relay contacts.
Switching of larger load currents can be accom-
plished with mercury pool relays; with this tech-
nique fast rise times can still be obtained, but the
large inertia of mercury pool relays limits the max-
imum repetition rate of load switching and makes
the clear display of the transient recovery charac-
teristic on oscilloscope more difficult.
Figure 5-5.

Transient Recovery Time Test Setup

5-32 To check the transient recovery time, pro-
ceed as follows:
a. Connect test setup shown in Figure 5-5.
b. Turn CURRENT controls fully clockwise.
c. Turn on supply and adjust VOLTAGE con-
trols until front panel ammeter indicates 5 amps
output current.
d. Close line switch on repetitive load
switch setup.
e. Set oscilloscope for internal sync and
lock on either 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 symmetrically displayed about the
horizontal center line of the oscilloscope. This
center line now represents the nominal output volt-
age defined in the specification.
h. Adjust the horizontal positioning control
so that the trace starts at a point coincident with a
major graticule division. This point is then repre-
sentative of 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 dis-
played.
k. Starting from the major graticule division
representative of time zero, count to the right 50µ-
sec and vertically 10mV. Recovery should be with-
in these tolerances as illustrated in Figure 5-6.
Figure 5-6.

Transient Recovery Time Waveforms

5-6