Hameg HM 1004-3 Series, Manual

Page: 28 / 36

Subject to change without notice
28
Triggering and Timebase Auto Set
calibration detent (fully ccw), otherwise the brightness of the
display is reduced drastically. The function is shown in the
following figures.
Fig. 1 shows a case where the holdoff control is in the minimum
position and various different waveforms are overlapped on
the screen, making the signal observation unsuccessful.
Fig. 2 shows a case where only the desired parts of the signal are
stably displayed.
B-Timebase (2nd Timebase)/
Triggering after Delay
Please note instrument specific information in section
“Controls and readout”. The most important controls
regarding this mode are
A/ALT - B (25), DEL.TRIG. - VAR.
(26), TIME/DIV. (24), DEL. POS.- HO (23)
and and
and and and TRS (9).
As mentioned before, triggering starts the timebase 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
timebase 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
timebase speed is increased (time coefficient reduced). The
X expansion by 10 may also be used, but again the expansion
factor is limited. The B timebase 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 timebase mode (A and B), the signal part to be
expanded must be selected with the aid of the intensified
sector on the A timebase trace. The B timebase 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 timebase
trace, change from alternate (A and B) to B timebase 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
timebase after the elapsed delay time.
Auto Set
The instrument specific information regarding this function is
part of the section
“Controls and Readout” paragraph
AUTO SET (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 (timebase)
mode is possible. In most cases no additional manual instru-
ment setting is required.
Briefly pressing the AUTO SET pushbutton causes the instru-
ment 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 mono channel mode or if in
DUAL mode for approx. 4 div height for each channel. This and
the following explanation regarding the automatic time coef-
ficient 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
timebase setting occurs randomly if complex signals consist-
ing 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”.
AUTO SET 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 timebase deflection coefficient calibrated
• AC trigger coupling (except DC trigger coupling)
• Alternate or B timebase 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