earthed conductors of other line powered devices, which
are connected to the oscilloscope or test object, e.g.
signal generators with anti-interference capacitors).
Sometimes the trace will disappear after an input signal
has been applied. The attenuator switch must then be
turned back to the left, until the vertical signal height is
only 3-8cm . With a signal amplitude greater than
1 60Vpp, an attenuator probe must be inserted before
the oscilloscope's vertical input. If, after applying the
signal, the trace is nearly blanked, the period of the signal
is probably substantially longer than the set value on the
TIMEBASE
switch. It should be turned to the left on an
adequately greater time coefficient.
Caution:
When connecting unknown signals to the
oscilloscope input, always use automatic triggering and
set the
DC-AC
input coupling switch to
AC.
The at
tenuator switch should initially be set to
20V/cm.
Operating Modes of the Y Amplifier
The required operating modes are selected on four
pushbuttons located in the Y-Section. For
Mono
opera
tion, all pushbuttons should be in the out position, the
instrument is then operating on
Channel I
only
Vox Mono
operation with
ChannelH,
the
CHI/II
pushbutton has to
be pressed. Automatically, the internal trigger voltage is
derived from Channel II. When the
DUAL
button is
depressed, the HM203 is in
Dual
channel operation. In
this mode, the channels are displayed consecutively
(alternate mode). This mode is not suitable for the display
of very low frequency signals (< 1 kHz), as the trace will
appear to flicker or jump. Under these conditions, the
ALT/CHOP
button should be depressed additionally
selecting chopped mode. In this position, both channels
then share the trace during each sweep period. For the
display of high frequency signals, the type of channel
switching selected is less important.
To select the
Add mode,
only the
ALT/CHOP (I
+
11)
but
ton should be depressed. The signals on both channels
are then added together. If in this mode Channel I is
inverted
(pushbutton
INVERT I
depressed), then the
dif
ference
between the two channels is displayed. For both
of these operating modes, the vertical position of the
trace depends on the setting of the
Y-POS.
controls of
both channels.
For
X -Y operation,
the pushbutton in the X-Section
marked
HOR. EXT.
must be depressed. The X signal is
then derived from the
Channel II
(HOR. INP.).
The
calibration of the X signal during X -Y operation is
determined by the setting o f the Channel H input
attenuator and variable control.
This means that the
sensitivity ranges and input impedances are identical for
both the X and Y axes. However, the
Y-POS. II
control is
disconnected in this mode. Its function is taken over by
the
X-POS.
control. It is important to note that the
X-MAGN. X5
pushbutton switch, normally used for
expanding the sweep, should not be operated in the X-Y
mode. It should also be noted that the bandwidth of the X
amplifier is approximately 2 .5 MHz (-3dB), and therefore
an increase in phase difference between both axes is
noticeable from 50kHz upwards.
Triggering and Timebase
In order to obtain a satisfactory stable display, the
timebase must be triggered synchronously with the test
signal. The trigger signal can be derived from the test
signal itself, when internal triggering is selected, or from
a frequency related signal applied to the external trigger
input.
If the
AT/NORM.
pushbutton in the X-Section is in the
out position
AT
(Automatic Triggering)
, the sweep
generator will be triggered automatically. In the
AT
posi
tion and with proper trigger control settings, the sweep
can be started by virtually all uncomplicated signals with
repetition rates above about 3 0 Hz and within the fre
quency range selected by the trigger coupling switch,
provided that the displayed signal height is at least
5mm
(trigger threshold for internal triggering). In the absence
of an adequate trigger signal or when the trigger controls
are misadjusted, the sweep free-runs and produces a
baseline (time axis) as a reference trace.
Automatic Trig
gering takes place without operating the
LEVEL
con
trol.
This trigger mode operates in principle also with ex
ternal triggering via the
TRIG. EXT.
connector. However,
the (synchronous) trigger voltage required for it should be
approximately in the 0.6-1 OVpp range.
With
Normal Triggering
(AT/NORM.
button depressed)
and
LEVEL
adjustment, the sweep can be started by
signals within the frequency range selected by the trigger
coupling switch. In the absence of an adequate trigger
signal or when the trigger controls (particularly the
LEVEL
control) are misadjusted, no trace is visible, i.e.
the screen is blanked completely. When using the inter
nal Normal Triggering mode, it is possible to trigger at
any amplitude point of a signal edge, even with very
complex signal shapes, by adjusting the
LEVEL
control.
Its adjusting range is directly dependent on the display
height, which should be at least
5mm.
If it is smaller than
1 cm, the
LEVEL
adjustment needs to be operated with a
sensitive touch. In the external Normal Triggering mode,
the same is valid relating to a small external trigger
voltage amplitude.
M8 20 3-4
