29
Subject to change without notice
amplitudes. Only a very exact trigger level adjustment makes a
single display possible. The use of the holdoff control simplifies
the right adjustment.
After specific use the holdoff control should be reset into its
calibration detent (fully ccw), otherwise the brightness of the
display is reduced drastically. The function is shown in the figures
1 and 2.
B-Time Base (2nd Time Base)/ Triggering after Delay
Please note instrument specific information in section “Controls
and readout”. The most important controls regarding this mode
are
A/ALT - B (26), DEL.TRIG. - VAR. (27), TIME/DIV. (25), DEL.
POS.- HO (24) and TRS (8).
As mentioned before, triggering starts the time base sweep and
unblanks the beam. After the maximum X deflection to the right,
the beam is blanked and flies back to the (left) start position.
After the hold off time has elapsed the sweep is started
automatically by the automatic trigger or the next trigger signal.
In normal triggering mode the automatic trigger is switched off
and the sweep will only start on receipt of a trigger signal. As the
trigger point is always at the trace start position, trace expansion
in X direction with the aid of the time base is limited to the display
always from the trace start.
Parts of the signal to be expanded which are displayed near the
trace end (right side of the screen) are lost when the time base
speed is increased (time coefficient reduced). The X expansion
by 10 may also be used, but again the expansion factor is limited.
The B time base solves such problems.
First the A time coefficient should be in a suitable setting to display
a complete signal period. After setting the instrument to alternate
time base mode (A and B), the signal part to be expanded must
be selected with the aid of the intensified sector on the A time
base trace. The B time base deflection coefficient should be at
least a tenth of the A time coefficient.
Higher A/B ratios (e.g. A: 1ms/div, B: 1µs/div = 1000fold
expansion) result in a drastically reduced B trace intensity. Within
certain limits this can be compensated by the intensity setting.
To avoid high contrast between the A and B time base trace,
change from alternate (A and B) to B time base mode. Then the
A trace is invisible.
The start position of the intensified sector on the A trace can be
stated as the delay time. It is related to the A trace start and the
A time coefficient.
The delay function delays the B trace start by a variable time
from the A trigger point. This allows the sweep to begin on any
portion of a signal (except the first millimeters). If the display
shows jitter, it is possible to select triggering of the B time base
after the elapsed delay time.
AUTOSET
The instrument specific information regarding this function is part
of the section
“Controls and Readout” paragraph AUTOSET
(2)
. As also mentioned in that section all controls are electronically
selected with the exception of the
POWER
and calibrator
frequency (CAL 1kHz/1MHz) pushbuttons as well as the
FOCUS
and
TR
(trace rotation) control. Thus automatic signal related
instrument set up in Yt (time base) mode is possible. In most
cases no additional manual instrument setting is required.
Briefly pressing the
AUTOSET
pushbutton causes the instrument
to switch over to the last Yt mode settings regarding CH I, CH II
and DUAL. If the instrument was operated in Yt mode, the actual
setting will not be affected with the exception of ADD mode
which will be switched off. At the same time the attenuator(s)
(VOLTS/DIV) are automatically set for a signal display height of
approx. 6 div in single channel mode or if in DUAL mode for
approx. 4 div height for each channel.
This and the following explanation regarding the automatic time
coefficient setting assumes that the pulse duty factor of the input
signal is approx. 1:1. The time deflection coefficient is also set
automatically for a display of approx. 2 signal periods. The time
base setting occurs randomly if complex signals consisting
several frequencies e.g. video signals are present. If cursor
voltage measurement is selected, AUTOSET also affects the
position of the CURSOR lines. Please note
AUTOSET (2)
in
section ”Controls and Readout”.
AUTOSET
sets the instrument automatically to the following
operating conditions:
AC or DC input coupling unaltered
or in GD condition the previously used setting
Internal triggering (channel I or channel II)
Automatic peak (value) triggering
Trigger level in electrical midrange position
Y deflection coefficient(s) calibrated
A time base deflection coefficient calibrated
AC trigger coupling (except DC trigger coupling)
Alternate or B time base mode switched off
X x10 magnifier switched off
Automatic X and Y position settings
A visible trace and readout intensities.
If DC trigger coupling had been selected, AC trigger coupling will
not be chosen and the automatic trigger is operative without the
peak value detection.
The X position is set to the CRT center as well as the Y-position in
CH I or CH II mode.
Small deviations due to tolerances of the
CRT and other components are unavoidable.
In DUAL mode
the channel I trace is set to the upper half and the channel II
trace to the lower half of the CRT.
The 1mV/div and 2mV/div deflection coefficients will not be
selected by AUTOSET as the bandwidth is reduced on these
settings.
Attention!
If a signal is applied with a pulse duty factor of approx.
400:1 or larger, an automatic signal display cannot be
performed. The pulse duty factor causes too low a Y
deflection coefficient (sensitivity too high) and too high a
time deflection coefficient (time base speed too slow) and
results in a display in which only the baseline is visible.
AUTOSET
